Review: The use of direct fed microbials to mitigate pathogens and enhance production in cattle
Abstract
McAllister, T. A., Beauchemin, K. A., Alazzeh, A. Y., Baah, J., Teather, R. M. and Stanford, K. 2011. Review: The use of direct fed microbials to mitigate pathogens and enhance production in cattle. Can. J. Anim. Sci. 91: 193–211. Direct-fed microbials (DFM) have been employed in ruminant production for over 30 yr. Originally, DFM were used primarily in young ruminants to accelerate establishment of the intestinal microflora involved in feed digestion and to promote gut health. Further advancements led to more sophisticated mixtures of DFM that are targeted at improving fiber digestion and preventing ruminal acidosis in mature cattle. Through these outcomes on fiber digestion/rumen health, second-generation DFM have also resulted in improvements in milk yield, growth and feed efficiency of cattle, but results have been inconsistent. More recently, there has been an emphasis on the development of DFM that exhibit activity in cattle against potentially zoonotic pathogens such as Escherichia coli O157:H7, Salmonella spp. and Staphylococcus aureus. Regulatory requirements have limited the microbial species within DFM products to organisms that are generally recognized as safe, such as lactic acid-producing bacteria (e.g., Lactobacillus and Enterococcus spp.), fungi (e.g., Aspergillus oryzae), or yeast (e.g., Saccharomyces cerevisiae). Direct-fed microbials of rumen origin, involving lactate-utilizing species (e.g., Megasphaera elsdenii, Selenomonas ruminantium, Propionibacterium spp.) and plant cell wall-degrading isolates of Butyrivibrio fibrisolvens have also been explored, but have not been commercially used. Development of DFM that are efficacious over a wide range of ruminant production systems remains challenging because[0] comprehensive knowledge of microbial ecology is lacking. Few studies have employed molecular techniques to study in detail the interaction of DFM with native microbial communities or the ruminant host. Advancements in the metagenomics of microbial communities and the genomics of microbial–host interactions may enable DFM to be formulated to improve production and promote health, responses that are presently often achieved through the use of antimicrobials in cattle.
Résumé
McAllister, T. A., Beauchemin, K. A., Alazzeh, A. Y., Baah, J., Teather, R. M. et Stanford, K. 2011. Survol de l'administration directe d'agents microbiens aux bovins pour atténuer l'incidence des microorganismes pathogènes et accroître la production. Can. J. Anim. Sci. 91: 193–211. On administre directement des agents microbiens aux ruminants depuis plus de trente ans. Au départ, on recourait surtout à cette pratique pour accélérer l’établissement de la microflore intestinale participant à la digestion et concourir à la santé du tube digestif chez les jeunes ruminants. Divers progrès ont cependant débouché sur des mélanges plus complexes qui avaient pour but d'améliorer la digestion des fibres et de prévenir l'acidose du rumen chez les sujets adultes. Consécutivement aux améliorations obtenues sur ces deux plans, des agents microbiens de deuxième génération ont concouru à rehausser le rendement laitier, la croissance et la valorisation des aliments chez les bovins, en dépit d'un manque d'uniformité au niveau des résultats. Plus récemment, on s'est intéressé au développement d'agents microbiens susceptibles de combattre les agents pathogènes à l'origine de certaines zoonoses, comme la souche O157:H7 d’Escherichia coli, Salmonella spp. et Staphylococcus aureus. La réglementation limite toutefois les espèces pouvant être administrées directement et qu'on estime généralement être inoffensives comme les bactéries lactiques (à savoir, espèces des genres Lactobacillus et Enterococcus), les cryptogames (par ex., Aspergillus oryzae) ou les levures (par ex., Saccharomyces cerevisiae). On a aussi exploré l'administration directe d'agents microbiens issus du rumen, comme les espèces utilisant le lactate (par ex., Megasphaera elsdenii, Selenomonas ruminantium, Propionibacterium spp.) et les isolats de Butyrivibrio fibrisolvens qui s'attaquent à la paroi cellulosique des cellules végétales, mais ces produits n'ont pas été commercialisés. L’élaboration d'agents microbiens efficaces pour une vaste gamme de systèmes d’élevage des ruminants continue de poser des difficultés faute d'une connaissance approfondie de l’écologie des microorganismes. Peu d’études ont recouru aux techniques moléculaires pour préciser l'interaction des agents microbiens avec la microflore naturelle ou avec le ruminant servant d'hôte. Il se peut que les progrès réalisés dans la métagénomique des populations d'unicellulaires et dans la génomique des interactions entre la bactérie et l'hôte permettent la formulation de produits qui amélioreront la production et bonifieront la santé, réactions qui résultent souvent déjà de l'administration d'antibiotiques aux bovins.
There is a new sense of importance in the development of effective direct fed microbials (DFM) for use in livestock production as concerns over the use of antibiotics in livestock production and the need for pathogen exclusion continue to grow. The terms “probiotics” and “DFM” are often used interchangeably, but in fact they are not truly synonymous. Probiotics are defined as “live microorganisms which when administered in adequate amounts, confer a health benefit on the host” (FAO-WHO 2001). Some probiotics, however, also contain enzymes and/or crude extracts in addition to live microbes (Yoon and Stern 1995). The Office of Regulatory Affairs of the US Food and Drug Administration and The Association of The American Feed Control Officials have defined DFM as feed products that contain only a source of live or naturally occurring microorganisms (Brashears et al. 2005).
Direct fed microbials have been used in the cattle industry for over 20 yr, primarily to improve growth performance, milk production or feed conversion efficiency (LeJeune and Wetzel 2007). They are administered directly to the animal in the form of an encapsulated bolus or mixed with the feed. A number of mechanisms whereby DFM may improve gut health and animal performance have been proposed (Fig. 1), but few of these have been directly examined in experiments with ruminants. The majority of studies that have attempted to define possible modes of action have examined the ability of DFM to favorably alter digestion in the rumen, through modulating ruminal acid production, promoting the establishment of desirable rumen microbial populations or enhancing ruminal fiber digestion.
Fig. 1
Direct fed microbials may also alter microbial activity in the lower digestive tract, but far fewer experiments have been conducted to specifically examine their impact on nutrient absorption or immune responses in the small or large intestine. Where studies have been conducted, they have primarily focused on the ability of DFM to competitively exclude undesirable pathogens such as Escherichia coli O157:H7 from the intestinal tract (Brashears et al. 2003). Bacterial DFM may also affect innate, humoral and cellular immune parameters as demonstrated by increased serum concentration of IgA, IgG and IgM and intestinal concentration of IgG and IgM in poultry (Haghighi et al. 2006) and swine (Zhang et al. 2008), respectively. Similar studies have not been conducted in ruminants, but an inflammatory response has been observed in steers fed a mixed DFM containing bacteria and yeast (Emmanuel et al. 2007). In poultry, DFM may also influence intestinal integrity by altering tight junctions and increasing mucus production by goblet cells (Chichlowski et al. 2007a), factors that could ultimately influence nutrient absorption. Finally, we are not aware of studies that have examined the extent to which DFM persist in the environment, a factor that would be an obvious benefit if fecal-oral transmission occurred and the DFM conferred health or performance benefits to other individuals in a herd. Studies that clearly define the extent to which DFM establish and persist as well as the mechanisms whereby they alter intestinal function are the key to developing the next generation of effective products.
TYPES OF DIRECT FED MICROBIALS
Rumen Microbes
Although the rumen contains a large number of bacteria, protozoa and fungi (Miron et al. 2001), only a few members of this complex community have been explored for their potential as DFM (Table 1). Most approaches have focused on the use of rumen bacteria to either alter the profile of fermentation products or detoxify plant secondary compounds such as mimosine (Jones et al. 2009). A few studies have explored the extent to which inoculation with ruminal fungi may improve fiber digestion (Lee et al. 2000; Sehgal et al. 2008), but the potential of rumen protozoa as a DFM has not been investigated.
Table 1
z
C, calves; D, dairy cattle; F, feedlot cattle; L, lamb.
y
Numbers within parenthesis indicate number of studies reported since 1991.
The majority of studies using rumen bacteria DFM have been targeted at enhancing ruminal lactic acid metabolism through inoculation with lactic acid-utilizing bacteria such as Megasphaera elsdenii (Klieve et al. 2003), Selenomonas ruminantium (Wiryawan and Brooker 1995) or Propionibacterium freudenreichii (Raeth-Knight et al. 2007).
Others have taken the approach of attempting to reduce the amount of lactic acid produced by introducing rumen bacteria (Prevotella bryantii 25A) that utilize starch, but produce fermentation end products other than lactic acid (Chiquette et al. 2008). The fibrolytic rumen bacteria Ruminococcus albus (Krause et al. 2001) and Ruminococcus flavefaciens (Chiquette et al. 2007) have also been used as a DFM in an effort to enhance fiber digestion, but with limited success. Logically, one might hypothesize that DFM derived from the rumen may more readily integrate into the microbial community as they are being introduced into the environment from which they were derived. Such a scenario would be advantageous if the DFM established and persisted within the microbial community, as it would eliminate the need for daily administration. However, cultured rumen bacteria frequently fail to persist in the rumen (Flint et al. 1989; Krause et al. 2000, 2001) and have often been only successfully established in gnotobiotic ruminants (Fonty et al. 1983). It is widely recognized that with repeated culture, many rumen bacteria undergo morphological and metabolic changes relative to their wild type counterparts (Groleau and Forsberg 1981; Stewart et al. 1997). Cultured rumen bacteria are not exposed to myriad selective pressures that are inherent to the intestinal environment and consequently may lack the fitness required to integrate or compete within rumen microbial communities.
Perhaps the greatest obstacle to the development of rumen-derived DFM is that many of the candidate microbes are obligate anaerobes, limiting cell yield and complicating their culture in commercial fermentation facilities. Media required for the growth of rumen microbes are often chemically complex, expensive and not well-defined as clarified rumen fluid is still an important ingredient of many formulations. Exclusion of oxygen during packaging and storage also becomes an issue and oxygen sensitivity precludes the administration of anaerobic DFM with feed. Consequently, rumen-based DFM have not been commercialized to date.
Lactic Acid-producing Bacteria
The majority of DFM used in cattle production contain at least one or more lactic acid- producing bacteria (LAB) with representative genera including Lactobacillus spp., Streptococcus spp., Pediococcus spp. and Enterococcus spp. These microbes have been administered to almost all classes of ruminant livestock (Table 1). In suckling calves, LAB are most often administered as a bolus or associated with a carrier paste, whereas in beef and dairy cattle they are more commonly administered through the diet. Additionally, LAB are frequently inoculated onto forages just prior to ensiling as a means of enhancing the preservation, feed value and aerobic stability of silage (Kang et al. 2009; Schmidt et al. 2009). In these cases viability of LAB during feed processing or ensiling is a key selection criterion for their usefulness as a DFM.
Lactic acid-producing bacteria are desirable as DFM as they lend themselves to industrial culture, are environmentally robust and have a number of mechanisms whereby they may alter or influence microbial communities. Obviously, lactic acid is one key antimicrobial compound produced by LAB that can disrupt the intraceullular pH of bacterial competitors (Servin 2004), but these bacteria are also known to produce antimicrobial peptides known as bacteriocins (see below). In the presence of oxygen, LAB can also produce hydrogen peroxide, which has been shown to limit Salmonella activity in vitro (Pridmore et al. 2008), but the role that this antimicrobial plays in the intestinal tract, where oxygen concentrations are limited, is unknown. Other compounds such as benzoic acid, diacetyl, mevalonolactone, methylhydantoin and reuterin can be produced by some, but not all strains of LAB (Brashears et al. 2005). In many commercial DFM, LAB are administered in combination with other bacteria or yeast to get a multi-factorial response to the use of these products. Although such an approach makes sense from a production perspective, from an experimental perspective it makes it very difficult to attribute performance or pathogen exclusion responses to a single microbial component within the DFM. The possibility of interactive effects of mixed DFM on performance parameters can also not be excluded.
Other Bacteria
Other bacteria such as Bacillus spp. and Bifidobacterium spp. have also been used as DFM, but primarily in poultry (Flint and Garner 2009). The ability of Bacillus spp. to form thermotolerant and environmentally stable endospores has obvious advantages in ensuring their survival during feed pelleting and prolonged storage. Although Bacillus spp. have been isolated from the rumen (Oyeleke and Okusanmi 2008) they are often present in low numbers and may only play a minor role in plant cell wall degradation. Strains of Bifidobacterium spp. have also been isolated from the rumen, but the strains used as DFM are not of rumen origin. In monogastrics, Bifidobacterium spp. colonize the intestinal tract shortly after birth (Liévin-Le Moal and Servin 2006) and play a key role against enterovirulent microorganisms involved in diarrhea (Servin 2004). In the rumen, Bifidobacterium spp. most likely play a role in starch digestion (Stewart et al. 1997), with their role in the metabolism of sugars in the lower intestinal tract being less pronounced than in monogastrics owing to the fact that only low levels of soluble carbohydrates escape the rumen. We are aware of only one study where Bifidobacterium spp. were included as a DFM that was administered to feedlot calves, and as they were administered along with three other microbial species, it is impossible to discern if any of the responses observed were due to their presence (Krehbiel et al. 2001).
Yeast Culture
Saccharomyces cerevisiae has been used extensively as a DFM for ruminants with the most common use being in dairy cattle (Table 1). Desnoyers et al. (2009) recently completed a comprehensive meta-analysis on the influence of S. cerevisiae on ruminal parameters and performance in dairy cows and concluded that this DFM increased dry matter intake, rumen pH, rumen volatile fatty acids (VFA) and organic matter digestibility, as well as decreasing rumen lactate concentration. These responses were more pronounced in dairy cattle fed higher levels of concentrate in the diet. Saccharomyces cerevisiae can metabolize lactic acid, but as they are aerobic, the extent to which they actively metabolize lactic acid within the anaerobic environment of the rumen remains a matter of debate. Alternatively, addition of S. cerevisiae may cause shifts in rumen bacterial populations, such as an increase in the numbers of fibrolytic rumen bacteria, a scenario that has been offered as an explanation for the improvements in fiber digestibility that are occasionally observed with yeast supplementation. Some have proposed that these shifts in bacterial populations reflect the ability of yeast to utilize the trace amounts of oxygen present in the rumen, thereby creating an environment that is more conducive for the activity of anaerobic cellulolytic bacteria (Jouany et al. 1999). Alternatively, others have proposed that the yeast culture itself contains micronutrients that simulate the growth of rumen microbial populations thereby altering rumen fermentation (Robinson and Erasmus 2009).
Crude enzyme extracts, as opposed to whole cells, are the primary form in which Aspergillus oryzae and Aspergillus niger have been added to the diets of ruminants. As these are extracts, in the strictest sense they are not true DFM. These preparations are primarily targeted at increasing fiber or starch digestion in the rumen, but may alter feed utilization in ruminants via several mechanisms (McAllister et al. 2001). As these extracts are often crude, it seems probable that some of these preparations contain viable fungal cells. However, as Aspergillus spp. are also aerobic, their impact on rumen fermentation as a result of direct metabolism or growth is likely minimal.
DIRECT FED MICROBIAL MODES OF ACTION
Bacteriocins
General Nature of Bacteriocins
Bacteriocins are a heterogeneous group of ribosomally synthesized antibacterial peptides and proteins and are perhaps the most characterized of the antimicrobials produced by bacterial DFM. They are usually capable of inhibiting bacteria closely related to the producing strain, which are presumably competing for the same ecological niche, but they may also inhibit a wider range of target organisms. In Gram-positive bacteria these substances consist primarily of cationic, amphipathic peptides which are divided into two main groups: lantibiotic (class I), and non-lantibiotic (class II) bacteriocins (Klaenhammer 1993; Eijsink et al. 2002; Nes et al. 2007).
The bacteriocins produced by Gram-positive organisms also include large, enzymatically active peptides (class III) and complex peptide-containing molecules (class IV). Bacteriocins produced by Gram-negative bacteria and archaea are similarly diverse (Riley and Wertz 2002; Gillor et al. 2008). Bacteriocin production has been identified in all major bacterial groups. Environmental surveys have identified prevalence levels of bacteriocin-producing isolates of 3 to 90% (Gordon and O'Brien 2006; Gillor et al. 2008), and it has been suggested that most bacteria produce at least one bacteriocin (Klaenhammer 1988). Consequently, bacteriocins likely play a significant role in the mode of action of most bacterial DFM.
Classes, Modes of Action, Spectrum of Activity
The bacteriocins produced by Gram-negative bacteria fall into two classes, colicins and microcins. The colicins, first described in E. coli (hence the name colicin) are large, heat labile peptides that generally kill their target organism by membrane permeabilization or by nucleic acid degradation (Riley and Wertz 2002). Microcins appear to be similar in many respects to the class I and II bacteriocins of Gram-positive bacteria, but kill through a variety of mechanisms (Duquesne et al. 2007). They are not as well characterized as the colicins. The bacteriocins produced by Gram-positives bacteria, historically most extensively studied among the lactic acid bacteria, comprise four distinct classes. The lantibiotics (class I) are small heat-stable peptides (20–35 amino acids for the mature peptide). The original translated peptide, or prebacteriocin, is generally significantly larger and undergoes extensive post-translational modification that includes cleavage of a leader peptide and modification of amino acid residues to form dehydroalanine, lanthionine, and/or 3-methyllanthionine residues (Twomey et al. 2002). They generally act by forming pores in the cytoplasmic membrane of the target cell or by interfering with cell wall synthesis, and in some cases have been shown to require interaction with specific target or docking molecules for optimal activity (Gillor et al. 2008).
The class II bacteriocins are also small heat-stable peptides that, like the lantibiotics, are synthesized with a leader peptide. However, post-translational processing is largely limited to cleavage of the leader peptide, and in most cases they do not contain modified amino acid residues (Drider et al. 2006). They act by forming pores in the cytoplasmic membrane of the target cell (Eijsink et al. 2002; Gillor et al. 2008).
The class III bacteriocins are large proteins that possess bactericidal enzyme activity (Nilsen et al. 2003), while class IV bacteriocins have lipid or carbohydrate moieties that are required for activity (Vermeiren et al. 2006). Less is known about the distribution or significance of these latter groups.
Production of Bacteriocins by Rumen Microorganisms
The first report of bacteriocin-like activity in a rumen isolate was by Iverson and Millis (1976), who described antimicrobial activity by isolates of Streptococcus bovis. Since that time there have been reports of production of antimicrobials by many rumen bacteria, and in many cases these have been confirmed as bacteriocins of classes I, II, or III. For example, a survey of 50 ruminal Butyrivibrio isolates demonstrated a high prevalence of antimicrobial production. Twenty-six of the 50 isolates exhibited activity against other strains of Butyrivibrio (Kalmokoff et al. 1996). These antimicrobials also showed activity against strains of clostridium, eubacterium, lachnospira, lactobacillus, ruminococcus and streptococcus. Two of those antimicrobials have been purified and characterized. One, butyrivibriocin OR79A, produced by Butyrivibrio fibrisolvens OR79, was a lantibiotic (class I) similar to lacticin 481 (Kalmokoff et al. 1999), while the second, butyrivibriocin AR10, produced by B. fibrisolvens AR10, is a circular, non-lantibiotic (class II) bacteriocin (Kalmokoff et al. 2003). Among the rumen cocci, R. albus 7 produces a heat-stable protein that inhibits R. flavefaciens FD-1 (Odenyo et al. 1994) and R. albus produces a heat-labile protein with inhibitory activity against R. flavefaciens (Chan and Dehority 1999). A rumen Enterococcus faecalis isolate, E. faecalis II/I, was shown to produce a bacteriocin identical to the heat labile class III bacteriocin enterolysin A, which was originally identified in the non-rumen isolate, E. faecalis LMG 2333 (Nilsen et al. 2003). Five of 33 rumen coccus isolates, 2 streptococci and 3 enterococci, were shown to carry homologues to the gene for this bacteriocin, enlA (Nigutova et al. 2007). Ruminococcus albus 7 also produces a class III bacteriocin, albusin 7, which is active against all tested strains of R. flavefaciens (Chen et al. 2004). A class I lantibiotic, bovicin HC5, is produced by S. bovis HC5 (Mantovani et al. 2002). Recent studies indicate that this lantibiotic may be as useful as monensin in limiting methane production and amino acid degradation in the rumen (Lee et al. 2002; Lima et al. 2009). A class II bacteriocin, bovicin 255, with activity against strains of butyrivibrio, enterococcus, and lactobacillus has been shown to be produced by a rumen isolate of Streptococcus gallolyticus (Whitford et al. 2001a). Another class II bacteriocin, lichenin, is produced by the rumen isolate Bacillus licheniformis 26 L-10/3RA. Lichenin shows activity against some streptococci, ruminococci, eubacteria, lactobacilli and strains of Butyrivibrio (Pattnaik et al. 2001).
Among the reports of antimicrobial activity production by rumen bacteria there are also a number of reports of probable bacteriocin production where the nature of the inhibitory agent has not been confirmed. Pseudobutyrivibrio xylanivorans Mz5 produces an uncharacterized antimicrobial compound active against strains of butyrivibrio and prevotella (Cepeljnik et al. 2003). Butyrivibriofibrisolvens JL5 has been shown to produce an antimicrobial membrane-active peptide with a comparatively wide spectrum of activity, active against strains of butyrivibrio, prevotella, clostridium, eubacterium, peptostreptococcus, ruminococcus, and fusobacterium (Rychlik and Russell 2002). A ruminal isolate of Lactobacillus fermentum produces an uncharacterized antimicrobial compound active against strains of S. bovis (Wells et al. 1997), and all four isolates of a novel rumen bacterium, Lachnobacterium bovis, produced an uncharacterized temperature-sensitive antimicrobial compound (Whitford et al. 2001b). Given the widespread presence of bacteriocins, it seems certain that some of the changes in microbial ecology observed with DFM of rumen origin arise from the presence of these antimicrobials. The consequences of resistance by rumen microorganisms to bacteriocins produced by DFM, and the effects of bacteriocins produced by rumen bacteria on the viability of DFM, are also likely to be significant.
Resistance to Bacteriocins
Resistance to bacteriocins can arise from many different sources. In bacteriocin producers, resistance to the produced bacteriocin is normally a function of a gene or genes that are expressed at the same time as the bacteriocin. More generalized resistance, such as the usual resistance of Gram-negative bacteria to bacteriocins produced by Gram-positive bacteria, may be due to barriers that limit access to the cytoplasmic membrane. These could include factors such as the Gram-negative outer membrane or a positively-charged surface layer, or the lack of a specific target or docking molecule on the cell surface. Proteases may also play a role. Resistance may also be acquired by susceptible organisms through the same general mechanisms as employed for other antibiotics: exclusion, degradation, or target modification (Eijsink et al. 2002). The extent to which development of resistance to bacteriocins influences the efficacy of DFM is unknown, but given that many DFM are administered to ruminants throughout the feeding period the possibility of resistance development should be given consideration.
Studies on the Role of Bacteriocins in DFM Response
Studies on the effect of bacteriocins introduced into the gastrointestinal environment have been limited. Only two specific bacteriocins have been examined, and both of these were effective in the rumen environment. In the first example, enterocin CCM 4231, produced by the rumen isolate Enterococcus faecium CCM4231 (Lauková and Mareková 1993) was shown to inhibit the growth of enterococci, staphylococci, listeria, and E. coli in the rumen environment (Lauková and Czikková 1998). In vitro studies of the class I lantibiotic bovicin HC5, produced by S. bovis HC5 (Mantovani et al. 2002) revealed that it may be as useful as monensin in limiting methane production and amino acid degradation in the rumen (Lee et al. 2002; Lima et al. 2009). Most studies of bacteriocin effects on rumen function have been less well defined. Cell-free supernatant from the bacteriocin-producer L. plantarum 80 inhibits methanogenesis (Nollet et al. 1998), but the mechanism of this effect has not been determined. Nisin- and pediocin-producing lactic acid bacteria have been shown to reduce intestinal colonization by vancomycin-resistant enterococci (Millette et al. 2008), but direct effects by bacteriocins have not been demonstrated. It has often been shown that colicinogenic strains of E. coli are inhibitory to pathogenic strains (Jordi et al. 2001). The probiotic E. coli strain Nissle 1917 produces microcins H47 and M (Patzer et al. 2003), and has been shown to reduce neonatal diarrhea in calves (von Buenau et al. 2005), possibly by interfering with the invasion of epithelial cells by Salmonella enterica var. typhimurium. However, this response appears to arise via a secreted component that is independent of microcin production (Altenhoefer et al. 2004). Again a specific role of the antimicrobial compounds in this protective effect has not been demonstrated.
DFM AND BIOFILMS
As in most aquatic environments, the overwhelming majority of microbes present in the intestinal tract of ruminants reside in complex communities known as biofilms. Microbial biofilms form on the surface of feed particles and play an integral role in feed digestion with substrate exchange occurring among community members (McAllister et al. 1994). Similarly, biofilms also form on the surface of intestinal tissues influencing nutrient transport and intestinal health (Cheng and McAllister 1997). As these microbes function as a community in a manner that is not unlike that of a multicellular organism (Nikolaev and Plakunov 2007), the mechanisms whereby foreign DFM may integrate into or alter community structure is not entirely clear.
The widespread occurrence of bacteriocin production across the microbial kingdom, and the high incidence of bacteriocin production and resistance in natural microbial communities, suggest that these compounds play an important role in determining the competitive fitness of microbial strains. However, the presence of non-producing, sensitive strains within the same communities raises the question of what that role might be, and how important these compounds are in determining the ability of a DFM to integrate with intestinal microbial communities in ruminants. The cost of bacteriocin production to the cell can be significant. For example, in Lantibiotic plantaricin NC8, 21 genes are involved in the regulation, synthesis, post-translational processing, immunity, and export of the bacteriocin (Navarro et al. 2008). Thus, the fate of a bacteriocin-producing strain in a complex environment is a balance between the production of antimicrobials to confer a competitive advantage vs. decreased reproduction due to the metabolic cost of bacteriocin synthesis. Expression of resistance genes alone also has a cost, though it is less than the cost of bacteriocin production.
Theoretical models indicate that the competition at a simplistic level resembles a paper/rock/scissors game where producers beat sensitive cells, resistants beat producers, and sensitives beat resistants under conditions where expression of resistance genes offers no competitive advantage (Czárán et al. 2002; Kerr et al. 2002; Riley and Wertz 2002). Biofilms, where micro-colonies interact at short range, tend to include bacteria that represent all three types. Production of the Gram-positive class I and II bacteriocins is generally regulated by a quorum-sensing mechanism, where high local cell densities, as occurs in biofilms, triggers bacteriocin production (Gobbetti et al. 2007; Nes et al. 2007). Quorum sensing, a proposed method of communication between bacterial cells by the release of small diffusible signal molecules, has been observed in rumen bacteria (Mitsumori et al. 2003) and likely plays an important role in the development and establishment of ruminal biofilms. At this point it is not known if introduced DFM and resident intestinal bacteria in ruminants speak the same quorum sensing language, although several quorum sensing mechanisms have been shown to be shared among widely differing microbial species (Dickschat 2010).
Natural biofilm populations with a high degree of diversity are predicted to tend toward a “hyper-immunity” state whereby many strains produce no toxins; many others produce only one, and only a few produce many, with all strains being resistant to most or many of the toxins. For example, in the case of the 50 butyrivibrio strains examined by Kalmokoff et al. (1996), many strains carrying the structural gene bviA did not express it (Kalmokoff et al. 1999), even though the gene was widely distributed in all the butyrivibrio groups examined (unpublished observations). The presence of homologous genes in a variety of genera suggests that these genes may be widely distributed by horizontal transfer (Ochman et al. 2000). Horizontal transfer of bacteriocin genes may allow organisms to become effective competitors in a previously unexplored niche (Lawrence 1999) and selection of DFM based on their ability to acquire genes coding for bacteriocins may be an approach to increasing their competitiveness in intestinal environments.
Establishment of DFM in intestinal communities appears more straightforward when it is accomplished through the production of an antimicrobial that specifically promotes competitive exclusion. Under these conditions DFM must simply expulse or prevent the establishment of the target microorganism thereby preventing biofilm formation. Specific integration of the DFM into biofilms would be more complex as it presumably would require the DFM to contribute some limiting or absent metabolic function to the microbial community. Biofilm communities are highly structured and the microbial consortia they contain function as a team to accomplish degradation of complex substrates such as starch and cellulose (McAllister et al. 1994). Occasionally, DFM may possess unique metabolic activities that promote their establishment within the intestinal tract, such as the ability of Synergistes jonesii to degrade mimosine in the rumen (Jones et al. 2009). Specific integration of DFM into biofilms needed for more complex functions such as the degradation of plant cells seems less likely, especially as most commercial DFM lack genes coding for the enzymes involved in the hydrolysis of plant cell walls. In these instances the provision of undefined nutrients or the use of secondary fermentation products may be a more plausible explanation for their mode of action.
IMMUNOMODULATION
Bacterial DFM may impact the host immune system via a number of mechanisms including up-regulation of cell-mediated immunity, increased antibody production and epithelial barrier integrity, reduction of epithelial cell apoptosis, enhanced dendritic cell–T cell interactions, heightened T cell association with lymph nodes and greater Toll-like receptor signalling (Lee et al. 2010). Stimulation of epithelial innate immunity is central to this response and may suppress intestinal inflammation by increased production of epithelial-derived TNF-α and restoration of epithelial barrier function (Pagnini et al. 2010). The impact of DFM on cytokine and chemokine production as well as T and B cell responses appear to depend on several factors including microbial composition of the DFM, the dosage and the duration of administration. For example, a mixed DFM consisting of L. casei, L. acidophilus, Bifidobacterium thermophilum and E. faecium increased expression of inflammatory cytokine IL-6, but decreased expression of the anti-inflammatory cytokine IL-10 in chicks (Chichlowski et al. 2007b). In other studies administration of a LAB-based DFM repressed IFN-γ and IL-12 levels in the intestinal tract of chickens and reduced intestinal colonization by Salmonella enterica (Haghighi et al. 2008). In contrast a Bacillus subtilis DFM had no impact on the expression of IFN-γ, IL-3, IL-4 in chickens (Fujiwara et al. 2009). Using microarrays, Brisbin et al. (2008) found that expression of IFN-γ, IFN-α, STAT2, STAT4, IL-18, MyD88 were all up-regulated in the cecal tonsil cells of chickens provided with a L. acidophilus DFM. Although numerous studies have measured changes in the expression of genes coding for various immune factors, very few have examined the signalling cascades that result in these responses being conferred from DFM to host.
The majority of studies that have attempted to define immunomodulation responses to DFM have been conducted within cell culture or with poultry or murine models (Hörmannsperger and Haller 2010; Lee et al. 2010). Most of these studies have also examined immune responses to DFM after challenge with specific intestinal pathogens with little work being conducted to define the impact of DFM on intestinal immunity in healthy hosts. Studying immunomodulation responses in ruminants is difficult due to their extended life cycle and the expense associated with getting sufficient animal numbers to draw meaningful conclusions. Direct fed microbial-mediated immune responses are likely more important in younger ruminants where intestinal populations are less established and the intestinal tract is potentially more susceptible to colonization by opportunistic pathogens. In mature dairy cows, intramammary infusion of Lactococcus lactis DPC 3147 was shown to increase IL-1β and IL-8 gene expression (Beecher et al. 2009), but the ability of this potential therapy to control mastitis has not been confirmed. Only one study reported that a combination of E. faecium and S. cerevisiae increased the concentration of the acute phase proteins, serum amyloid A, lipopolysaccharide binding protein, and haptoglobin in plasma (Emmanuel et al. 2007). However, a linkage between alterations in intestinal function as a result of the DFM and changes in plasma concentrations of these acute phase proteins was not established.
Modulation of Ruminal Fermentation
Yeast culture (S. cerevisiae)
Active dry yeast (S. cerevisiae) and yeast cultures that contain yeast plus culture medium are increasingly used in ruminant feeding to improve animal performance (Desnoyers et al. 2009; Robinson and Erasmus 2009). Commercial products vary widely in the strains of S. cerevisiae they contain and the number of viable yeast cells present. Desnoyers et al. (2009) summarized the findings from 110 research papers representing a broad range of yeast products and feeding conditions and reported a mean increase in milk production of 0.8 kg d−1 due to supplemental yeast. In a more selective review of research conducted using three commercial yeast products, Robinson and Erasmus (2009) reported a milk production response of 0.9 kg d−1 to added yeast. In both reviews, the beneficial effects of yeast were greatest in low fiber diets, consistent with observed improvements in fiber digestion and ruminal fermentation of cattle fed yeast. The effects of added yeast culture on rumen fermentation are complex [as reviewed by Chaucheyras-Durand et al. (2008)], and not well understood. Live yeast has been shown to stimulate the growth and activities of some ruminal fiber-degrading microorganisms, although this work has mostly been done in vitro (Martin and Nisbet 1992; Chaucheyras-Durand et al. 2008). Various mechanisms for the increase in fiber degradation due to yeast supplementation have been proposed. Yeast may scavenge oxygen within the rumen, which might stimulate the growth of cellulolytic bacteria given that most ruminal microorganisms are highly sensitive to the presence of oxygen (Newbold et al. 1996). In support of this oxygen-scavenging theory, the redox potential of ruminal fluid in cows is lower in the presence of live yeasts (Marden et al. 2008), indicating that yeast can strengthen the reducing power of ruminal fluid. It is also possible that yeast provide rumen bacteria with growth factors, including organic acids, B vitamins, and amino acids (Callaway and Martin 1997). In addition, yeast products may stimulate the growth of fibrolytic bacteria by preventing sub-acute ruminal acidosis (Chaucheyras-Durand et al. 2008).
Sub-acute ruminal acidosis is characterized by repeated bouts of low ruminal pH, with the pH recovering after each bout (Krause and Oetzel 2006). Long bouts (>4 h) of low pH (<6.0) negatively affect fiber digestion (Russell and Wilson 1996) and decrease the absorptive capacity of the ruminal epithelium (Krehbiel et al. 1995). These bouts of low pH occur when VFA production is rapid and exceeds the capacity of the rumen to maintain equilibrium. With time, the VFA are absorbed, buffered or passed from the rumen, causing the pH to rise. As a consequence, ruminal pH follows a cyclical pattern that includes periods defined as sub-acute ruminal acidosis. During sub-acute ruminal acidosis, lactic acid concentrations remain low (<5 mM) (Nagaraja and Titgemeyer 2007). In a limited number of cases, sub-acute ruminal acidosis develops into acute acidosis, during which ruminal pH drops drastically (<5.0) and fails to recover over time (Owens et al. 1998). Acute acidosis is usually caused by elevated concentrations of lactic acid in the rumen (>50 mM) as a result of an abrupt increase in the intake of rapidly fermentable carbohydrates (Nagaraja and Titgemeyer 2007). Callaway and Martin (1997) reported that yeast culture stimulated the growth of two lactate-utilizing bacteria, S. ruminantium and M. elsdenii, in vitro. If yeast help prevent lactic acid from accumulating in the rumen, it follows that providing yeast to cows could theoretically help prevent sub-acute acidosis from developing into acute acidosis. However, sub-acute acidosis is seldom related solely to lactic acid accumulation (Krause and Oetzel 2006); thus, this mode of action is unlikely to account for the acidosis-prevention response that is occasionally observed with yeast supplementation.
The effects of yeast on stabilizing ruminal pH may depend on the diet or the strain of yeast. In fact, many studies report no effect of yeast and yeast culture on rumen pH (Wiedmeier et al. 1987; Erasmus et al. 2005; Longuski et al. 2009), and in some studies, rumen pH was actually lowered by feeding yeast culture to dairy cows (Harrison et al. 1988). Despite many studies that indicate no effect of yeast on rumen pH, there are studies showing that yeast products elevate ruminal pH. For example, Williams et al. (1991) fed yeast culture to three steers and nadir pH following the meal was higher when yeast was fed. However, caution must be used when interpreting these results, because the yeast and control diets were fed at different times, confounding the treatment comparison with time. Additional evidence for the pH stabilizing effects of yeast is given in several recent papers, although few cows were used in these studies. Marden et al. (2008) fed three lactating dairy cows either no yeast or live yeast (5×1010 CFU d−1) in a Latin square design. Feeding yeast helped elevate nadir pH following the morning meal (from 5.55 to 5.95) and the response was equal to that of providing 150 g d−1 of sodium bicarbonate. It is not known whether the response to yeast would have occurred had sodium bicarbonate been included in the basal diet. In another study, Bach et al. (2007) fed dairy cows either no yeast or live yeast (1×1010 CFU d−1) in a crossover design. Average rumen pH was higher when yeast was supplemented than when no yeast was provided (6.05 vs. 5.46). The effects of yeast on rumen pH appear to depend on the strain of yeast and the dose rate. For example, in an unpublished study in our laboratory, dairy cows were fed two different strains of yeast (1×1010 CFU d−1). Strain 1 had no effect on pH variables, whereas Strain 2 substantially lowered mean pH compared with the control (5.98 vs. 6.27) and increased the hours that pH was below 5.8 (7.5 vs 2.9 h d−1). Strain 2 had been selected based on its ability to increase the rate of fiber digestion in vitro, which may have increased the rate of production and subsequent accumulation of VFA in the rumen.
There is compelling evidence to indicate that yeast products improve production efficiency of dairy cows. The improvement is likely due to a number of interacting factors. However, of primary importance is their beneficial effects on fiber digestibility, especially in cows fed low fiber diets where lactic acid metabolism by DFM may offset the low rumen pH that can depress the activity of cellulolytic bacteria and protozoa. There is also some limited evidence to suggest that some yeast products may help stabilize rumen pH, but that is not always the case. Whether yeast products reduce the risk of acidosis in dairy cows probably depends on the strain of yeast, the dose rate, and the presence and nature of other acidotic risk factors.
Bacterial DFM and Ruminal Fermentation
There is evidence that bacterial DFM can modify the rumen environment in a manner that may enhance animal productivity (Krehbiel et al. 2003; Beauchemin et al. 2006). In terms of their impact on ruminal fermentation, the main bacterial species used in DFM products can be considered in two categories: lactic acid producers and lactic acid utilizers (or propionate producers). Commercial DFM products often combine various organisms; thus, their modes of action are usually intertwined (Fig. 2). The rationale for feeding lactic acid producing bacteria, such as E. faecium and Lactobacillus spp., to ruminants is based on the contention that these bacteria produce lactic acid in the rumen, which promotes the growth of lactic acid utilizing bacteria. However, small, transient increases in ruminal lactic acid concentration are almost impossible to measure in vivo. Consequently, an increased concentration of propionate in rumen fluid has been used to signify increased numbers of lactic acid-producing bacteria as most lactic acid utilizers convert lactate directly to propionate or indirectly through succinate to propionate. As such, Beauchemin et al. (2003) fed E. faecium EF212 (EF; 6×109 CFU d−1) to feedlot finishing cattle and measured an increased concentration of propionate in rumen fluid, as well as a numerical increase in the numbers of lactic acid-utilizing bacteria. Proliferation of the lactic acid-utilizing bacteria would be beneficial in the event of any sudden increase in lactic acid concentration in the rumen. Numerous ruminal bacterial species ferment lactic acid, with M. elsdenii and S. ruminantium spp. lactilytica being predominant culturable lactate-fermenting organisms in grain-fed animals (Nagaraja and Titgemeyer 2007). In most animals, the inherent ruminal population of lactic acid-utilizing bacteria ensures that any lactic acid produced is rapidly metabolized, and it therefore does not accumulate. As a consequence of this, lactic acid concentration in the rumen of most ruminants is low (<5 mM; Owens et al. 1998). Lactic acid utilizers can be slow to adapt to rapid changes in diet composition; thus, abrupt changes in diet composition, amount of feed consumed or feed delivery can lead to a sudden increase in lactic acid concentration. Lactic acid is a very potent acid (pKa 3.9 vs. 4.9 for VFA); therefore, accumulation of lactic acid causes ruminal pH to decline rapidly (Nagaraja and Titgemeyer 2007), causing subacute and even acute acidosis (Krause and Oetzel 2006). Low ruminal pH also activates lactate dehydrogenase, the enzyme involved in converting pyruvate to lactate, a response that exacerbates the accumulation of lactic acid in the rumen (Owens et al. 1998). Furthermore, feeding a large amount of starch can also increase ruminal concentrations of free glucose, which increases the competitiveness of lactate-producing bacteria such as S. bovis in the rumen (Owens et al. 1998). Some bacterial DFM products are composed of both lactic acid producers and lactic acid utilizers in an effort to ensure that any lactic acid produced is immediately metabolized. These combination products have been explored mainly for use in feedlot cattle fed high grain diets [as reviewed by Krehbiel et al. (2003)], with some limited work in dairy cows (Raeth-Knight et al. 2007).
Fig. 2
Other bacterial DFM products contain only lactic acid utilizers, with Propionibacterium being the predominant organism (Francisco et al. 2002; Stein et al. 2006; Weiss et al. 2008). Propionibacterium are natural inhabitants of the rumen that utilize lactic acid and produce propionate. Ruminal populations of Propionibacterium (mainly P. acidipropionici) typically range from 103 to104 CFU mL−1 (Davidson and Rehberger 1995). The rationale for feeding Propionibacterium is to further ensure concentrations of lactic acid in the rumen remain low, while increasing production of propionate (Lehloenya et al. 2008), the major precursor for gluconeogenesis in ruminants (Huntington 1990). Feeding supplemental Propionibacterium can help improve the energy status of ruminants, in particular, lactating dairy cows (Stein et al. 2006; Aleman et al. 2007). Use of Propionibacterium alone has increased propionate concentrations in the rumen in some studies (Stein et al. 2006; Lehloenya et al. 2008), but not all (Ghorbani et al. 2002). There is little published data on the effects of Propionibacterium on rumen pH. Stein et al. (2006) reported that dairy cows fed a high dose of Propionibacterium P169 (6×1011 CFU d−1) had lower pH than cows on a low dose (6×1010 CFU d−1) or the control with values of 6.65, 6.94, and 6.86, respectively. Ruminal fluid samples were taken via intubation in that study, and therefore are considerably higher than expected had they been measured using indwelling pH probes. Other studies have reported no effects of feeding Propionibacterium on rumen pH in steers (Ghorbani et al. 2002, strain P15 at 1×109 CFU d−1; Lehloenya et al. 2008, strain P169 at 6×1011 CFU d−1).
There has also been interest in using M. elsdenii as a DFM for cattle because it metabolizes lactic acid (Kung and Hession 1995; Klieve et al. 2003). In an early study, steers were inoculated with M. elsdenii strain YE34, and then rapidly adapted to a grain-based diet. The YE34 rapidly established in the rumen after dosing with 106 cell equivalents mL−1 of rumen fluid being measured immediately upon providing the DFM, with this number increasing 100-fold 4 d after inoculation. When the control cattle were switched to the grain diet, wild types of M. elsdenii eventually also became predominant members of the microbial population, but required an additional week to become established at a level similar to the DFM. It is thought that rapid establishment of M. elsdenii would be protective against acidosis for ruminants during the periods of diet transition. To test this hypothesis, dairy cows were fed very high grain diets (60 and 70%, dry matter basis) with M. elsdenii dosed on days 2, 10, and 20 post-partum (Hagg 2007). Contrary to expectations, the DFM had no effect on pH or lactic acid concentrations in the rumen. Another rumen bacterium, P. bryantii (strain 25A), selected for its ability to grow rapidly on starch and produce propionate rather than lactate (Rodriguez 2003), has recently been evaluated in dairy cows (Chiquette et al. 2008). When this strain was administered (2×1011 cells d−1) to dairy cows through a rumen cannula from −3 to 7 wk postpartum, there was no change in milk production, but milk fat content (3.9 vs. 3.5%) and total VFA tended to be higher in inoculated cows than in control cows. However, rumen pH or concentrations of propionate and lactate were not affected by treatment.
Pathogen Exclusion
As livestock may intermittently become reservoirs of pathogenic bacteria (Callaway et al. 2008a), DFM have also been developed specifically to limit the shedding of potential food-borne pathogens. In cattle, work with DFM on pathogen exclusion has focused primarily on reducing the shedding of E. coli O157 (Elam et al. 2003; Zhao et al. 2003; Callaway et al. 2004; LeJeune and Wetzel 2007), the bacterium responsible for hemorrhagic colitis and hemolytic uremic syndrome in humans. The most extensively studied DFM for cattle is L. acidophilus strain NP51, which has been found to reduce shedding of E. coli O157:H7 by cattle by 48 to 80% when fed at 109 CFU (Brashears et al. 2003; Younts-Dahl et al. 2004, 2005; Stephens et al. 2007a, b). Recently, Tabe et al. (2008) found that an alternative strain of L. acidophilus (BT1386) reduced fecal shedding of E. coli O157 in feedlot steers, but had no impact on the shedding of Salmonella sp. Reduced fecal shedding of Salmonella spp. in cattle was documented by Stephens et al. (2007b) in steers fed a combination of 109 CFU L.acidophilus NP51 and 109 CFU P. freudenreichii NP24. However, unlike the work of Younts-Dahl et al. (2005) these researchers did not detect a dose-dependent reduction in the shedding of E. coli O157 with increasing levels of L. acidophilus NP51 in the diet.
Although the ability of DFM to reduce the prevalence of pathogens in livestock has been reported, few studies have specifically addressed the possible mechanisms responsible for this phenomenon (Fig. 3). Pathogens that have become firmly established in the gastro-intestinal tract (GIT) through the formation of mature biofilms may pose a greater challenge for DFM-mediated removal than those that are transiently associated with digesta. Cells within biofilms are known to alter their gene expression and may become thousands of times more resistant to antimicrobial agents (Mah and O'Toole 2001; Ito et al. 2009). Under these conditions pathogenic bacteria may become insensitive to antimicrobials (e.g., bacteriocins, organic acids) produced by DFM. Although recently it has been shown that a released exopolysaccharide (r-EPS) produced by L. acidophilus A4 inhibited biofilm formation by E. coli O157:H7 (Kim et al. 2009). In the newborn, complex microbial biofilms have yet to establish and under these conditions DFM may be more likely to cause favorable alterations in the microbial ecology of the digestive tract. Studies in piglets showed that a lactobacilli-based DFM promoted colonization of a beneficial microbiota and reduced intestinal colonization by Clostridium perfringens (Siggers et al. 2008). Consequently, DFM may be more efficacious at eliminating pathogens from the intestinal tract of young as compared with mature ruminants.
Fig. 3
Competitive exclusion is one of the predominant mechanisms whereby DFM may eliminate pathogens from the intestinal tract (LeJeune and Wetzel 2007; Callaway et al. 2008b). Sherman et al. (2005) demonstrated that adhesion of L. acidophilus strain R0052 and L. rhamnosus strain R0011 to intestinal epithelium cells (T84) reduced subsequent colonization by both E. coli O157:H7 and E. coli O127:H6. Similarly, Chen et al. (2007) determined that surface-layer proteins produced by L. crispatus ZJ001 inhibited the adhesion of S. typhimurium and E. coli O157:H7 to HeLa cells. More recently, Johnson-Henry et al. (2008) confirmed that pre-treatment of T84 cells with L. rhamnosus limited morphological changes in cells by reducing the formation of attaching and effacing lesions after exposure to E. coli O157:H7. These researchers proposed that this observation arises from the ability of L. rhamnosus to prevent redistribution of tight-junction proteins at the epithelial surface. Lactobacillus plantarum has also been shown to stabilize tight junction proteins in intestinal epithelial cells exposed to enteropathogenic E. coli (Qin et al. 2009).
Direct binding to the intestinal epithelium is only one of many mechanisms whereby DFM may exclude pathogens. In some instances DFM may alter gene expression in targeted pathogens, a phenomenon that was recently demonstrated when a cell-free medium from L. acidophilus strain La-5 was shown to inhibit the colonization of specific-pathogen-free mice by E. coli O157:H7 (Medellin-Pena and Griffiths 2009). As binding of E. coli O157:H7 to the GIT is also mediated by the hormones epinephrine and norepinephrine secreted by the host (Sperandio et al. 2003), other mechanisms for competitive exclusion perhaps involving communication between the DFM and the host also likely exist, but require further characterization.
Other key mechanisms resulting in competitive exclusion of pathogenic organisms by DFM arise from the competition for limiting nutrients or production of compounds that are toxic to the pathogens (Callaway et al. 2004). Metabolism of gluconic acid, a constituent of intestinal mucus, which stimulates in vitro growth of E. coli O157 (Chang et al. 2004) was identified by Fox et al. (2009) as a mechanism for competitive exclusion of E. coli O157 by non-pathogenic E. coli. Inhibitory metabolites including bacteriocins and organic acids were proposed, but not directly evaluated by Lee et al. (2008) as a mechanism for in vitro competitive exclusion of E. coli O157:H7 by L. paracasei ATCC 25598 and L. rhamnosus GG. The presence of bacteriocins was verified by Schamberger and Diez-Gonzalez (2004) when these researchers isolated seven colicins from nonpathogenic strains of E. coli.
Although competition for nutrients and production of bacteriocins has been verified as mechanisms for competitive exclusion of pathogenic organisms by DFM, control of pathogenic organisms by production of organic acids appears less likely. Our laboratory has recently shown that some acid-adapted strains of E. coli O157:H7 can remain viable for extended periods of time, even at a pH of 2.5 (Yang et al. 2010). Jacobsen et al. (2009) recently confirmed this acid tolerance when they determined that the acidic threshold for growth was pH 4.3 using a selection of E. coli O157:H7 strains chosen for diversity from a library of 2600 isolates. Consequently, animal performance would likely suffer due to acidosis (Nagaraja 2007) long before acid- mediated competitive exclusion of this pathogenic organism occurs. Within the bovine GIT, pH at the ileum commonly ranges between 7.4 and 7.9 (Christiansen and Webb 1990), falling to 6.0 in the large intestine and feces from hind gut fermentation of starch in cattle receiving high-concentrate diets (Berg et al. 2004), a pH range that is conducive to both the growth and establishment of E. coli O157:H7.
The heightened immune responses as a result of DFM described above may also aide the host in eliminating pathogenic organisms from the intestinal tract. Oetzel et al. (2007) demonstrated that a DFM containing E. faecium and S. cerevisiae reduced requirements for antibiotic treatment for second lactation dairy cows, although the mechanism(s) for this response were not identified. Davis et al. (2007) were able to provide some insight into the relationship between probiotics and host immunity by demonstrating that a DFM containing L. brevis increased the number of mucin-producing goblet cells and altered numbers of antigen-presenting cells and T cells within the jejunal villi of pigs. More recently, Szabo et al. (2009) demonstrated that a DFM containing E. faecium NCIMB 10415 enhanced production of specific antibodies (serum IgM and IgA) against Salmonella serovar Typhmurium DT104 in weanling piglets. Similarly, Lessard et al. (2009) found an increase in IgA and enhanced resistance to exterotoxigenic E. coli infection in piglets after use of a DFM containing Pediococcus acidilactici and S. cerevisiae boulardii. The mechanisms by which DFM control pathogenic organisms are in some cases exceedingly complex and due to the plethora of microorganisms used as constituents of DFM, much additional study will be required to establish a basic framework for improved and uniform efficacy. However, as many mechanisms by which DFM control pathogenic organisms have been verified relatively recently, accelerated expansion of our knowledge in this area is likely. For cattle, new DFM, which are capable of controlling a variety of pathogenic organisms, will be perhaps most suitable for use in young calves.
CONCLUSION
Direct fed microbials have the potential to reduce the current reliance on antimicrobials as a tool to promote health and optimize productivity in cattle. However, for DFM to be adopted, positive production responses as a result of their administration must be predictable and consistent. Advances in molecular biology are just now providing the enabling technologies that allow microbial–host interactions to be examined at a level that was previously impossible using traditional microbial culture or histological techniques. Metagenomics and transcriptomics should provide new insight into how DFM alter microbial ecology within the GI tract and gene expression in the host. As these relationships between DFM and increased production and improved health become defined, selection of DFM for properties such as the exclusion of specific pathogens or optimization of host immune function will become more feasible. Only through a growing emphasis on mechanistic research will the true extent to which DFM improve the microbial community as well as the ruminant host come to light. Learning the way DFM work is the key to the development of more effective DFM.
ACKNOWLEDGEMENTS
The researchers thank K. Jakober and K. Munns for their editorial assistance and S. Torgunrud for excellent graphical support.
References
Abas I., Kutay H. C., Kahraman R., Toker N. Y., Özçelik D., Ates F., and Kaçakci A. Effects of organic acid and bacterial direct-feed microbial on fattening performance of Kivircik-male yearling lambs Pak. J. Nutr. 2007 6 149 -154
Adams M. C., Luo J., Rayward D., King S., Gibson R., and Moghaddam G. H. Enzymes, direct fed microbials and plant extracts in ruminant nutrition Anim. Feed Sci. Technol. 2008 145 41 -52
Aikman P. C., Henning P. H., Horn C. H., and Humphries D. J. Use of Megasphaera elsdenii NCIMB41125 as a probiotic for early-lactation dairy cows: Effects on rumen pH and fermentation J. Anim. Sci. 2009 87 E. Suppl. 2 288 (Abstr.)
Aleman M. M., Stein D. R., Allen D. T., Perry E., Lehloenya K. V., Rehberger T. G., Mertz K. J., Jones D. A., and Spicer L. J. Effects of feeding two levels of propionibacteria to dairy cows on plasma hormones and metabolites J. Dairy Res. 2007 74 146 -153
Al-Saiady M. Y. Effect of probiotic bacteria on immunoglobulin G concentration and other blood components of Newborn calves J. Anim. Vet. Adv. 2010 9 604 -609
Altenhoefer A., Oswald S., Sonnenborn U., Enders C., Schulze J., Hacker J., and Oelschlaeger T. A. The probiotic Escherichia coli strain Nissle 1917 interferes with invasion of human intestinal epithelial cells by different enteroinvasive bacterial pathogens FEMS Immunol. Med. Microbiol. 2004 40 223 -229
Arthur T. M., Bosilevac J. M., Kalchayanand N., Wells J. E., Shackelford S. D., Wheeler T. L., and Koohmaraie M. Evaluation of a direct-fed microbial product effect on the prevalence and load of Escherichia coli O157:H7 in feedlot cattle J. Food Prot. 2010 73 366 -371
Aydin R., Yanar M., Kocyigit R., Diler A., and Ozkilicci T. Z. Effect of direct-fed microbials plus enzyme supplementation on the fattening performance of Holstein young bulls at two different initial body weights Afr. J. Agric. Res. 2009 5 548 -552
Bach A., Iglesias C., and Devant M. Daily rumen pH pattern of loose-housed dairy cattle as affected by feeding pattern and live yeast supplementation Anim. Feed Sci. Technol. 2007 136 156 -163
Beauchemin K. A., Krehbiel C. R., and Newbold C. J. Mosenthin R., Zentec J., and Zebrowska T. Enzymes, bacterial direct-fed microbials and yeast: Principles for use in ruminant nutrition The biology of nutrition in growing animals 2006 Amsterdam, the Netherlands Elsevier Science B.V. 251 -284
Beauchemin K. A., Yang W. Z., Morgavi D. P., Ghorbani G. R., Kautz W., and Leedle J. A. Z. Effects of bacterial direct-fed microbials and yeast on site and extent of digestion, blood chemistry, and subclinical ruminal acidosis in feedlot cattle J. Anim. Sci. 2003 81 1628 -1640
Beecher C., Daly M., Berry D. P., Klostermann K., Flynn J., Meaney W., Hill C., McCarthy T. V., Ross R. P., and Giblin L. Administration of a live culture of Lactococcus lactis DPC 3147 into the bovine mammary gland stimulates the local host immune response, particularly IL–1 beta and IL-8 gene expression J. Dairy Res. 2009 76 340 -348
Berg J., McAllister T. A., Bach S., Stilborn R., Hancock D., and LeJeune J. Escherichia coli O157:H7 excretion by commercial feedlot cattle fed either barley-or corn-based finishing diets J. Food Prot. 2004 67 666 -671
Brashears M. M., Amezquita A., and Jaroni D. Lactic acid bacteria and their uses in animal feeding to improve food safety Adv. Food Nutr. Res. 2005 50 1 -31
Brashears M. M., Galyean M. L., Loneragan G. H., Mann J. E., and Killinger-Mann K. Prevalence of Escherichia coli O157:H7 and performance by beef feedlot cattle given Lactobacillus direct-fed microbials J. Food Prot. 2003 66 748 -754
Brisbin J. T., Zhou H., Gong J., Sabour P., Akbari M. R., Haghighi H. R., Yu H., Clarke A., Sarson A. J., and Sharif S. Gene expression profiling of chicken lymphoid cells after treatment with Lactobacillus acidophilus cellular components Dev. Comp. Immunol. 2008 32 563 -574
Callaway E. S. and Martin S. A. Effects of a Saccharomyces cerevisiae culture on ruminal bacteria that utilize lactate and digest cellulose J. Dairy Sci. 1997 80 2035 -2044
Callaway T. R., Anderson R. C., Edrington T. S., Genovese K. J., Bischoff K. M., Poole T. L., Jung Y. S., Harvey R. B., and Nisbet D. J. What are we doing about Escherichia coli O157:H7 in cattle? J. Anim. Sci. 2004 82E E93 -E99
Callaway T. R., Carr M. A., Edrington T. S., Anderson R. C., and Nisbet D. J. Diet, Escherichia coli O157:H7 and cattle: a review after 10 years Curr. Issues Mol. Biol. 2008a 11 67 -80
Callaway T. R., Edrington T. S., Anderson R. C., Harvey R. B., Genovese K. J., Kennedy C. N., Venn D. W., and Nisbet D. J. Probiotics, prebiotics and competitive exclusion for prophylaxis against bacterial disease Anim. Health Res. Rev. 2008b 9 217 -225
Cepeljnik T., Zorec M., Kostanjsek R., Nekrep F. V., and Marinsek-Logar R. Is Pseudobutyrivibrio xylanivorans strain Mz5T suitable as a probiotic? An in vitro study. Folia Microbiol (Praha) 2003 48 339 -345
Chan W. W. and Dehority B. A. Production of Ruminococcus flavefaciens growth inhibitor(s) by Ruminococcus albus Anim. Feed Sci. Technol. 1999 77 61 -71
Chang D. E., Smalley D. J., Tucker D. L., Leatham M. P., Norris W. E., Stevenson S. J., Anderson A. B., Brissom D. C., Laux P. S., Cohen P. S., and Conway T. Carbon nutrition of Escherichia coli in the mouse intestine Proc. Natl. Acad. Sci. 2004 101 7427 -7432
Chaucheyras-Durand F., Faqir F., Ameilbonne A., Rozand C., and Martin C. Fates of acid-resistant and non-acid-resistant Shiga toxin-producing Escherichia coli strains in ruminant digestive contents in the absence and presence of probiotics Appl Environ Microbiol. 2010 76 640 -647
Chaucheyras-Durand F., Walker N. D., and Bach A. Effects of active dry yeasts on the rumen microbial ecosystem: Past, present and future Anim. Feed Sci. Technol. 2008 145 5 -26
Chen J., Stevenson D. M., and Weimer P. J. Albusin B, a bacteriocin from the ruminal bacterium Ruminococcus albus 7 that inhibits growth of Ruminococcus flavefaciens Appl. Environ. Microbiol. 2004 70 3167 -3170
Chen X., Xu J., Shuai J., Chen J., Zhang Z., and Fang W. The S-layer proteins of Lactobacillus crispatus strain ZJ001 is responsible for competitive exclusion against Escherichia coli O157:H7 and Salmonella typhimurium Int. J. Food Microbiol. 2007 115 307 -312
Cheng K. J. and McAllister T. A. Hobson P. N. and Stewart C. S. Compartmentation in the rumen The rumen microbial ecosystem 1997 2nd ed. London, UK Blackie Academic and Professional 492 -522
Chiquette J., Allison M. J., and Rasmussen M. A. Prevotella bryantii 25A used as a probiotic in early-lactation dairy cows: Effect on ruminal fermentation characteristics, milk production, and milk composition J. Dairy Sci. 2008 91 3536 -3543
Chiquette J., Talbot G., Markwell F., Nili N., and Forster R. J. Repeated ruminal dosing of Ruminococcus flavefaciens NJ along with a probiotic mixture in forage or concentrate-fed dairy cows: Effect on ruminal fermentation, cellulolytic populations and in sacco digestibility Can. J. Anim. Sci. 2007 87 237 -249
Chichlowski M., Croom J., McBride B. W., Havenstein G. B., and Koci M. D. Metabolic and physiological impact of probiotics or direct-fed-microbials on poultry: a brief review of current knowledge Int. J. Poult. Sci. 2007a 6 694 -704
Chichlowski M., Croom J., McBride B. W., Daniel L., Davis G., and Koci M. D. Direct-fed microbial PrimaLac and salinomycin modulate whole-body and intestinal oxygen consumption and intestinal mucosal cytokine production in the broiler chick Poult. Sci. 2007b 86 1100 -1106
Christiansen M. L. and Webb K. E. Intestinal acid flow, dry matter, starch and protein digestibility and amino acid absorption in beef cattle fed a high-concentrate diet with defluorinated rock phosphate, limestone or magnesium oxide J. Anim. Sci. 1990 68 2105 -2118
Czárán T. L., Hoekstra R. F., and Pagie L. Chemical warfare between microbes promotes biodiversity Proc. Natl. Acad. Sci. USA 2002 99 786 -790
Davidson C. A. and Rehberger T. G. Characterization of Propionibacterium isolated from the rumen of lactating dairy cows Proc. Am. Soc. Microbiol. 1995 1 -6 [Online] Available: http://192.220.59.24/resources/research_dairy_22.pdf [2010 May 11].
Davis M. E., Borwn D. C., Baker A., Bos K., Dirain M. S., Halborrk E., Johnson Z, Maxwell C., and Rehberger T. Effect of direct-fed microbial and antibiotic supplementation on gastrointestinal microflora, mucin histochemical characterization, and immune populations of weaning pigs Livestock Sci. 2007 108 249 -253
Desnoyers M., Giger-Reverdin S., Bertin G., Duvaux-Ponter C., and Sauvant D. Meta-analysis of the influence of Saccharomyces cerevisiae supplementation on ruminal parameters and milk production of ruminants J. Dairy Sci. 2009 92 1620 -1632
Dickschat J. S. Quorum sensing and bacterial biofilms Nat. Prod. Rep. 2010 27 343 -369
Drider D., Fimland G., Hechard Y., McMullen L. M., and Prevost H. The continuing story of class IIa bacteriocins Microbiol. Mol. Biol. Rev. 2006 70 564 -582
Duquesne S., Petit V., Peduzzi J., and Rebuffat S. Structural and functional diversity of microcins, gene-encoded antibacterial peptides from enterobacteria J. Mol. Microbiol. Biotechnol. 2007 13 200 -209
Eijsink V. G., Axelsson L., Diep D. B., Havarstein L. S., Holo H., and Nes I. F. Production of class II bacteriocins by lactic acid bacteria; an example of biological warfare and communication A. Van. Leeuw. 2002 81 639 -654
Elam N. A., Gleghorn J. F., Rivera J. D., Galyean M. L., Defoor P. J., Brashears M. M., and Younts-Dahl S. M. Effects of live cultures of Lactobacillus acidophilus (strains NP45 and NP51) and Propionibacterium freudenreichii on performance, carcass, and intestinal characteristics, and Escherichia coli strain O157 shedding of finishing beef steers J. Anim. Sci. 2003 81 2686 -2698
Emmanuel D. G. V., Jafari A., Beauchemin K. A., Leedle J. A. Z., and Ametaj B. N. Feeding live cultures of Enterococcus faecium and Saccharomyces cerevisiae induces an inflammatory response in feedlot steers J. Anim. Sci. 2007 85 233 -239
Erasmus L. J., Robinson P. H., Ahmadi A., Hinders R., and Garrett J. E. Influence of prepartum and postpartum supplementation of a yeast culture and monensin, or both, on ruminal fermentation and performance of multiparous dairy cows Anim. Feed Sci. Technol. 2005 122 219 -239
FAO/WHO Health and nutritional properties of probiotics in food including powder milk with live lactic acid bacteria Report of a Joint FAO/WHO expert consultation on evaluation of health and nutritional properties of probiotics in food including powder milk with live lactic acid bacteria 2001 Argentina Córdoba 1 -4 2001 Oct.
Fleige S., Preißinger W., Meyer H. H. D., and Pfaff M. W. Effect of lactulose on growth performance and intestinal morphology of pre-ruminant calves using a milk replacer containing Enterococcus faecium Animal 2007 1 367 -373
Flint J. F. and Garner M. R. Feeding beneficial bacteria: A natural solution for increasing efficiency and decreasing pathogens in animal agriculture J. Appl. Poult. Res. 2009 18 367 -378
Flint H. J., Bisset J., and Web J. Use of antibiotic resistance mutations to track strains of obligately anaerobic bacteria introduced into the rumen of sheep J. Appl. Bacteriol. 1989 67 177 -183
Fonty G., Jouany J. P., Thivend P., Gouet P., and Senaud J. A descriptive study of rumen digestion in meroxenic lambs according to the nature and complexity of the microflora Reprod. Nutr. Dev. 1983 23 857 -873
Fox J. T., Drouillard J. S., and Nagaraja T. G. Competitive exclusion Escherichia coli cultures on E. coli O157 growth in batch culture ruminal or fecal microbial fermentation Foodborne Pathog. Dis. 2009 6 193 -199
Francisco C. C., Chamberlain C. S., Waldner D. N., Wettemann R. P., and Spicer L. J. Propionibacteria fed to dairy cows: Effects on energy balance, plasma metabolites and hormones, and reproduction J. Dairy Sci. 2002 85 1738 -1751
Fujiwara K., Yamazaki M., Abe H., Nakashima K., Yakabe Y., Otuska M., Ohbayashi Y., Kato Y., Namai K., Toyoda A., Miyaguchi Y., and Nakamura Y. Effect of Bacillus subtilis var. natto fermented soybean on growth performance, microbial activity in the caeca and cytokine gene expression of domestic meat type chickens J. Poult. Sci. 2009 46 116 -122
Ghorbani G. R., Morgavi D. P., Beauchemin K. A., and Leedle J. A. Z. Effects of bacterial direct-fed microbials on ruminal fermentation, blood variables, and the microbial populations of feedlot cattle J. Anim. Sci. 2002 80 1977 -1985
Gillor O., Etzion A., and Riley M. A. The dual role of bacteriocins as anti- and probiotics Appl. Microbiol. Biotechnol. 2008 81 591 -606
Gobbetti M., De Angelis M., Di Cagno R., Minervini F., and Limitone A. Cell-cell communication in food related bacteria Int. J. Food Microbiol. 2007 120 34 -45
Gordon D. M. and O'Brien C. L. Bacteriocin diversity and the frequency of multiple bacteriocin production in Escherichia coli Microbiology 2006 152 3239 -3244
Groleau D. and Forsberg C. W. Cellulolytic activity of the rumen bacterium Bacteroides succinogenes Can. J. Microbiol. 1981 27 517 -530
Hagg F. M. The effect of Megasphaera elsdenii, a probiotic, on the productivity and health of Holstein cows MSc. thesis, 2007 South Africa University of Pretoria [Online] Available: http://upetd.up.ac.za/thesis/available/etd-08202008-131928/unrestricted/dissertation.pdf [2010 May 11].
Haghighi H. R., Abdul-Careem M. F., Dara R. A., Chambers J. R., and Shariff S. Cytokine gene expression in chicken cecal tonsils following treatment with probiotics and salmonella infection Vet. Microbiol. 2008 126 225 -233
Haghighi H. R., Gong J., Gyles C. L., Hayes M. A., Zhou H., Sanei B., Chambers J. R., and Sharif S. Probiotics stimulate production of natural antibodies in chickens Am. Soc. Microbiol. 2006 13 975 -980
Harrison G. A., Hemken R. W., Dawson K. A., Harmon R. J., and Barker K. B. Influence of addition of yeast culture supplement to diets of lactating cows on ruminal fermentation and microbial-populations J. Dairy Sci. 1988 71 2967 -2975
Henning P. H., Horn C. H., Leeuw K.-J., Meissner H. H., and Hagg F. M. Effect of ruminal administration of the lactate-utilizing strain Megasphaera elsdenii (Me) NCIMB 41125 on abrupt or gradual transition from forage to concentrate diets Anim. Feed Sci. Technol. 2010 157 20 -29
Hörmannsperger G. and Haller D. Molecular crosstalk of probiotic bacteria with the intestinal immune system: Clinical relevance in the context of inflammatory bowel disease Int. J. Med. Microbiol. 2010 300 63 -73
Huntington G. B. Energy metabolism in the digestive tract and liver of cattle: influence of physiological state and nutrition Reprod. Nutr. Dev. 1990 30 35 -47
Ito A., Taniuchi A., Thithiwat M., Kawata K., and Okabe S. Increased antibiotic resistance of Escherichia coli in mature biofilms Appl. Environ. Microbiol. 2009 75 4093 -4100
Iverson W. G. and Mills N. F. Bacteriocins of Streptococcus bovis Can. J. Microbiol. 1976 22 1040 -1047
Jacobsen L., Durso L., Conway T., and Nickerson K. W. Escherichia coli O157:H7 and other E. coli strains share physiological properties associated with intestinal colonization Appl. Environ. Microbiol. 2009 75 4633 -4635
Jatkauskas J. and Vrotniakien V. Effect of L-plantarum, Pediococcus acidilactici, Enterococcus faecium and L-lactis microbial supplementation of grass silage on the fermentation characteristics in rumen of dairy cows Vet. Zootec. 2007 40 29 -34
Johnson-Henry K. C., Donato K. A., Shen-Tu G., Gordanpour M., and Sherman P. M. Lactobacillus rhamnosus strain GG prevents enterohemorrhagic Escherichia coli O157:H7 induced changes in epithelial barrier function Infect. Immunol. 2008 76 1340 -1348
Jones R. J., Coates D. B., and Palmer B. Survival of the rumen bacterium Synergistes jonesii in a herd of droughtmaster cattle in north Queensland Anim. Prod. Sci. 2009 48 643 -645
Jordi B. J., Boutaga K., Heeswijk C. M. V., Knapen F. V., and Lipman L. J. Sensitivity of Shiga toxin-producing Escherichia coli (STEC) strains for colicins under different experimental conditions FEMS Microbiol. Lett. 2001 204 329 -334
Jouany J.-P., Mathieu F., Sénaud J., Bohatier J., Bertin G., and Mercier M. Influence of protozoa and fungal additives on ruminal pH and redox potential S. Afr. J. Anim. Sci. 1999 29 65 -66
Kalmokoff M. L., Bartlett F., and Teather R. M. Are rumen bacteria armed with bacteriocins? J. Dairy Sci. 1996 79 2297 -2306
Kalmokoff M. L., Cyr T. D., Hefford M. A., Whitford M. F., and Teather R. M. Butyrivibriocin AR10, a new cyclic bacteriocin produced by the ruminal anaerobe Butyrivibrio fibrisolvens AR10: characterization of the gene and peptide Can. J. Microbiol. 2003 49 763 -773
Kalmokoff M. L., Lu D., Whitford M. F., and Teather R. M. Evidence for production of a new lantibiotic (Butyrivibriocin OR79A) by the ruminal anaerobe Butyrivibrio fibrisolvens OR79: characterization of the structural gene encoding Butyrivibriocin OR79A Appl. Environ. Microbiol. 1999 65 2128 -2135
Kalmus P., Orro T., Waldmann A., Lindjärv R., and Kask K. Effect of yeast culture on milk production and metabolic and reproductive performance of early lactation dairy cows Acta. Vet. Scand. 2009 51 32 -39
Kang T. W., Adesogan A. T., Kim S. C., and Lee S. S. Effects of an esterase-producing inoculant on fermentation, aerobic stability and neutral detergent fiber digestibility of corn silage J. Dairy Sci. 2009 92 732 -738
Kerr B., Riley M. A., Feldman M. W., and Bohannan B. J. Local dispersal promotes biodiversity in a real-life game of rock-paper-scissors Nature 2002 418 171 -174
Kim S.-W., Standorf D. G., Roman-Rosario H., Yokoyama M. T., and Rust S. R. Potential use of Propionibacterium acidipropionici, strain DH42, as a direct-fed microbial for cattle J. Anim. Sci. 2000 78 Suppl. 1 292
Kim Y., Oh S., and Kim S. H. Released exopolysaccharide (r-EPS) produced from probiotic bacteria reduce biofilm formation of enterohemorrhagic Escherichia coli O157:H7 Biochem. Biophys. Res. Commun. 2009 379 324 -329
Klaenhammer T. R. Bacteriocins of lactic acid bacteria Biochimie 1988 770 337 -349
Klaenhammer T. R. Genetics of bacteriocins produced by lactic acid bacteria FEMS Microbiol. Rev. 1993 12 39 -86
Klieve A. V., Hennessy D., Ouwerkerk D., Forster R. J., Mackie R. I., and Attwood G. T. Establishing populations of Megasphaera elsdenii YE 34 and Butyrivibrio fibrisolvens YE 44 in the rumen of cattle fed high grain diets J. Appl. Microbiol. 2003 95 621 -630
Krause M. K. and Oetzel G. R. Understanding and preventing subacute ruminal acidosis in dairy herds: a review Anim. Feed Sci. Technol. 2006 126 215 -236
Krause D. O., Bunch R. J., Conlan L. L., Kennedy P. M., Smith W. J., Mackie R. I., and McSweeney C. S. Repeated ruminal dosing of Ruminococcus spp. does not result in persistence, but changes in other microbial populations occur that can be measured with quantitative 16S-rRNA-based probes Microbiology 2001 147 1719 -1729
Krause D. O., Smith W. J. M., Ryan F. M. E., Mackie R. I., and McSweeny C. S. Use of 16S-rRNA based techniques to investigate the ecological succession of microbial populations in the immature lamb rumen: tracking of a specific strain of inoculated Ruminococcus and interactions with other microbial populations in vivo Microbiol. Ecol. 2000 38 365 -376
Krehbiel C. R., Berry B. A., Reeves J. M., Gill D. R., Smith R. A., Step D. L., Choat W. T., and Ball R. L. Effects of feed additives fed to sale barn-origin calves during the receiving period: Animal performance, health and medical costs Okla. Agr. Exp. Stn. 2001 [Online] Available: http://www.ansi.okstate.edu/research/research-reports–1/2001/2001%20Krehbiel%20Research%20Report.pdf. [2010 May 11].
Krehbiel C. R., Britton R. A., Harmon D. L., Wester T. J., and Stock R. A. The effects of ruminal acidosis on volatile fatty acid absorption and plasma activities of pancreatic enzymes in lambs J. Anim. Sci. 1995 73 3111 -3121
Krehbiel C. R., Rust S. R., Zhang G., and Gilliland S. E. Bacterial direct-fed microbials in ruminant diets: Performance response and mode of action J. Anim. Sci. 2003 81 E120 -132E
Kung L. Jr and Hession A. O. Preventing in vitro lactate accumulation in ruminal fermentations by inoculation with Megasphaera elsdenii J. Anim. Sci. 1995 73 250 -256
Lauková A. and Czikková S. Inhibition effect of enterocin CCM 4231 in the rumen fluid environment Lett. Appl. Microbiol. 1998 26 215 -218
Lauková A. and Mareková M. Antimicrobial spectrum of bacteriocin-like substances produced by rumen staphylococci Folia Microbiol. 1993 38 74 -76
Lawrence J. G. Gene transfer, speciation, and the evolution of bacterial genomes Curr. Opin. Microbiol. 1999 2 519 -523
Lee K., Lillehoj H. S., and Siragusa G. R. Direct-fed microbials and their impact on the intestinal microflora and immune system of chickens J. Poult. Sci. 2010 47 106 -114
Lee S. S., Ha J. K., and Cheng K. J. Influence of an anaerobic fungal culture administration on in vivo ruminal fermentation and nutrient digestion Anim. Feed Sci. Technol. 2000 88 201 -217
Lee S. S., Hsu J. T., Mantovani H. C., and Russell J. B. The effect of bovicin HC5, a bacteriocin from Streptococcus bovis HC5, on ruminal methane production in vitro FEMS Microbiol. Lett. 2002 217 51 -55
Leeuw K.-J., Siebrits F. K., Henning P. H., and Meissner H. H. Effect of Megasphaera elsdenii NCIMB 41125 drenching on health and performance of steers fed high and low roughage diets in the feedlot S. Afr. J. Anim. Sci. 2009 39 337 -348
Lehloenya K. V., Krehbiel C. R., Mertz K. J., Rehberger T. G., and Spicer L. J. Effects of Propionibacteria and yeast culture fed to steers on nutrient intake and site and extent of digestion J. Dairy Sci. 2008 91 653 -662
LeJeune J. T. and Wetzel A. N. Preharvest control of Escherichia coli O157 in cattle J. Anim. Sci. 2007 85 73 -80
Lema M., Williams L., and Rao D. R. Reduction of fecal shedding of enterohemorrhagic Escherichia coli O157:H7 in lambs by feeding microbial feed supplement Small Rumin. Res. 2001 39 31 -39
Lessard M., Dupuis M., Gagnon N., Nadeau E., Matte J. J., Goulet J., and Fairbrother J. M. Administration of Pediococcus acidilactici or Saccharomyces cerevisiae boulardii modulates development of porcine mucosal immunity and reduces intestinal bacterial translocation after Escherichia coli challenge J. Anim. Sci. 2009 87 922 -934
Liévin-Le Moal V. and Servin A. L. The front line of enteric host defense against unwelcome intrusion of harmful microorganisms: mucins, antimicrobial peptides, and microbiota Clin. Microbiol. Rev. 2006 19 315 -337
Lima J. R., Ribon Ade O., Russell J. B., and Mantovani H. C. Bovicin HC5 inhibits wasteful amino acid degradation by mixed ruminal bacteria in vitro FEMS Microbiol. Lett. 2009 292 78 -84
Liou L., Sheng H., Ferens W., Schneider C., Hristov A. N., Yoon I., and Hovde C. J. Reduced carriage of Escherichia coli O157:H7 in cattle fed yeast culture supplement Prof. Anim. Sci. 2009 5 553 -558
Longuski R. A., Ying Y., and Allen M. S. Yeast culture supplementation prevented milk fat depression by a short-term dietary challenge with fermentable starch J. Dairy Sci. 2009 92 160 -167
Mah T.-F. and O'Toole G. A. Mechanism of biofilm resistance to antimicrobial agents Trends Microbiol. 2001 9 34 -39
Mantovani H. C., Hu H., Worobo R. W., and Russell J. B. Bovicin HC5, a bacteriocin from Streptococcus bovis HC5 Microbiology 2002 148 3347 -3352
Marden J. P., Julien C., Monteils V., Auclair E., Moncoulon R., and Bayourthe C. How does live yeast differ from sodium bicarbonate to stabilize ruminal pH in high-yielding dairy cows? J. Dairy Sci. 2008 91 3528 -3535
Martin S. A. and Nisbet D. J. Effect of direct-fed microbials on rumen microbial fermentation J. Dairy Sci. 1992 75 1736 -1744
McAllister T. A., Bae H. D., Jones G. A., and Cheng K. J. Microbial attachment and feed digestion in the rumen J. Anim. Sci. 1994 72 3004 -3018
McAllister T. A., Hristov A. N., Beauchemin K. A., Rode L. M., and Cheng K. J. Bedford M. and Partridge G. Enzymes in ruminant diets Enzymes in farm animal nutrition 2001 Wallingford, Oxon, UK CABI Publishing 273 -298
Medellin-Pena M. J. and Griffiths M.W. Effect of molecules secreted by Lactobacillus acidophilus Strain La-5 on Escherichia coli O157:H7 colonization Appl. Environ. Microbiol. 2009 75 1165 -1172
Millette M., Cornut G., Dupont C., Shareck F., Archambault D., and Lacroix M. Capacity of human nisin- and pediocin-producing lactic acid bacteria to reduce intestinal colonization by vancomycin-resistant enterococci Appl. Environ. Microbiol. 2008 74 1997 -2003
Miranda R. L. A., Mendoza M. G. D., Barcena-Gama J. R., Gonzalez M. S. S., Ferrara R., Ortega C. M. E., and Cobos P. M. A. Effect of Saccharomyces cerevisiae or Aspergillus oryzae cultures and NDF level on parameters of ruminal fermentation Anim. Feed Sci. Technol. 1996 63 289 -296
Miron J., Ben-Ghedalia D., and Morrison M. Invited review: adhesion mechanisms of rumen cellulolytic bacteria J. Dairy Sci. 2001 84 1294 -1309
Mitsumori M., Du L. M., Kajikawa H., Kurihara M., Tajima K., Hai J., and Takenaka A. Possible quorum sensing in the rumen microbial community: detection of quorum-sensing singnal molecules from rumen bacteria FEMS Microbiol. Let. 2003 219 47 -52
Nagaraja T. G. and Titgemeyer E. C. Ruminal acidosis in beef cattle: The current microbiological and nutritional outlook J. Dairy Sci. 2007 90 E. Suppl. E17 -E38
Navarro L., Rojo-Bezares B., Saenz Y., Diez L., Zarazaga M., Ruiz-Larrea F., and Torres C. Comparative study of the pln locus of the quorum-sensing regulated bacteriocin-producing L. plantarum J51 strain Int. J. Food Microbiol. 2008 128 390 -394
Nes I. F., Diep D. B., and Holo H. Bacteriocin diversity in Streptococcus and Enterococcus J. Bacteriol. 2007 189 1189 -1198
Newbold C. J., McIntosh F. M., and Wallace R. J. Mode of action of the yeast Saccharomyces cerevisiae as a feed additive for ruminants Br. J. Nutr. 1996 76 249 -261
Nigutova K., Morovsky M., Pristas P., Teather R. M., Holo H., and Javorsky P. Production of enterolysin A by rumen Enterococcus faecalis strain and occurrence of enlA homologues among ruminal Gram-positive cocci J. Appl. Microbiol. 2007 102 563 -569
Nikolaev Y. A. and Plakunov V. K. Biofilm – “City of Microbes” or an analogue of multicellular organisms? Microbiology 2007 76 125 -138
Nilsen T., Nes I. F., and Holo H. Enterolysin A, a cell wall-degrading bacteriocin from Enterococcus faecalis LMG 2333 Appl. Envron. Microbiol. 2003 69 2975 -2984
Nisbet D. J. and Martin S. A. Effect of a Saccharomyces cerevisiae culture on lactate utilization by the ruminal bacterium Selenomonas ruminantium J. Anim. Sci. 1991 69 4628 -4633
Nocek J. E., Kautz W. P., Leedle J. A., and Allman J. G. Ruminal supplementation of direct-fed microbials on diurnal pH variation and in situ digestion in dairy cattle J. Dairy Sci. 2002 85 429 -433
Nocek J. E., Kautz W. P., Leedle J. A. Z., and Block E. Direct-fed microbial supplementation on the performance of dairy cattle during transition period J. Dairy. Sci. 2003 86 331 -335
Nollet L., Mbanzamihigo L., Demeyer D., and Verstraete W. Effect of the addition of Peptosteptococcus productus ATCC 35244 on reductive acetogenesis in the ruminal ecosystem after inhibition of methanogenesis by cell-free supernatant of Lactobacilus plantarum 80 Anim. Feed Sci. Technol. 1998 71 49 -66
Ochman H., Lawrence J. G., and Groisman E. A. Lateral gene transfer and the nature of bacterial innovation Nature 2000 405 299 -304
Odenyo A. A., Mackie R. I., Stahl D. A., and White B. A. The use of 16S rRNA-targeted oligonucleotide probes to study competition between ruminal fibrolytic bacteria: development of probes for Ruminococcus species and evidence for bacteriocin production Appl. Environ. Microbiol. 1994 60 3688 -3696
Oetzel G. R., Emery K. M., Kautz W. P., and Nocek J. E. Direct-fed microbial supplementation and health performance of pre- and post-partum dairy cattle: a field trial J. Dairy Sci. 2007 90 2058 -2068
O'Toole P. W and Cooney J. C. Probiotic bacteria influence the composition and function of the intestinal microbiota Interdiscip. Perspect. Infect. Dis. 2008 2008 175 -285
Owens F. N., Secrist D. S., Hill W. J., and Gill D. R. Acidosis in cattle: A review J. Anim. Sci. 1998 76 275 -286
Oyeleke S. B. and Okusanmi T. A. Isolation and characterization of cellulose hydrolysing microorganism from the rumen of ruminants Afr. J. Biotech. 2008 7 1503 -1504
Pagnini C., Saeed R., Bamias G., Arseneau K. O., Pizarro T. T., and Cominelli F. Probiotics promote gut health through stimulation of epithelial innate immunity Proc. Natl. Acad. Sci. USA 2010 107 454 -459
Pattnaik P., Kaushik J. K., Grover S., and Batish V. K. Purification and characterization of a bacteriocin-like compound (Lichenin) produced anaerobically by Bacillus licheniformis isolated from water buffalo J. Appl. Microbiol. 2001 91 636 -45
Patzer S. I., Baquero M. R., Bravo D., Moreno F., and Hantke K. The colicin G, H and X determinants encode microcins M and H47, which might utilize the catecholate siderophore receptors FepA, Cir, Fiu and IroN Microbiology 2003 149 2557 -2570
Pridmore R. D., Pittet A. C., Praplan F., and Cavadini C. Hydrogen peroxide production by Lactobacillus johnsonii NCC 533 and its role in anti-Salmonella activity FEMS Microbiol. Lett. 2008 283 210 -215
Qiao G. H., Shan A. S., Ma N., Ma Q. Q., and Sun Z. W. Effect of supplemental Bacillus cultures on rumen fermentation and milk yield in Chinese Holstein cows J. Anim. Physiol. Anim. Nutr. (Berl) 2009 94 429 -436
Qin H., Zhang Z., Hang X., and Jiang Y. L. plantarum prevents Enteroinvasive Escherichia coli-induced tight junction proteins changes in intestinal epithelial cells BMC Microbiol. 2009 9 63 -68
Raeth-Knight M. L., Linn J. G., and Jung H. G. Effect of direct-fed microbials on performance, diet digestibility, and rumen characteristics of Holstein dairy cows J. Dairy Sci. 2007 90 1802 -1809
Riley M. A. and Wertz J. E. Bacteriocin diversity: ecological and evolutionary perspectives Biochimie 2002 84 357 -64
Robinson P. H. and Erasmus L. J. Effects of analyzable diet components on responses of lactating dairy cows to Saccharomyces cerevisiae based yeast products: A systematic review of the literature Anim. Feed Sci. Technol. 2009 149 185 -198
Rodriguez F. Control of lactate accumulation in ruminants using Prevotella bryantii Ph.D. thesis. 2003 Ames, IA Iowa State University
Russell J. B. and Wilson D. B. Why are ruminal cellulolytic bacteria unable to digest cellulose at low pH? J. Dairy Sci. 1996 79 1503 -1509
Rychlik J. L. and Russell J. B. Bacteriocin-like activity of Butyrivibrio fibrisolvens JL5 and its effect on other ruminal bacteria and ammonia production Appl. Environ. Microbiol. 2002 68 1040 -1046
Schamberger G. P. and Diez-Gonzalez F. Characterization of colicinogenic Escherichia coli strains inhibitory to enterohaemorrhagic Escherichia coli J. Food Prot. 2004 67 486 -492
Schmidt R. J., Hu W., Mills J. A., and Kung L. Jr The development of lactic acid bacteria and Lactobacillus buchneri and their effects on the fermentation of alfalfa silage J. Dairy Sci. 2009 92 5005 -5010
Sehgal J. P., Jit D., Puniya A. K., and Singh K. Influence of anaerobic fungal administration on growth, rumen fermentation and nutrient digestion in female buffalo calves J. Ani. Feed Sci. 2008 17 510 -518
Servin A. L. Antagonistic activities of lactobacilli and bifidobacteria against microbial pathogens FEMS Microbiol. Rev. 2004 28 405 -440
Sherman P. M., Johnson-Henry K. C., Yeung H. P., Ngo P. S. C., Goulet J., and Tompkins T. A. Probiotics reduce enterohemorrhagic Escherichia coli O157:H7 and enteropathogenic E. coli O127:H6-induced changes in polarized T84 epithelial cell monolayers by reducing bacterial adhesion and cytoskeletal rearrangements Infect. Immun. 2005 73 5183 -5188
Siggers R. H., Siggers J., Boye M., Thymann T., Molbak L., Lesser T., Hensen B. B., and Sangild T. Early administration of probiotics alters bacterial colonization and limits diet-induced gut dysfunction and severity of necrotic enterocolitis in pre-term pigs J. Nutr. 2008 138 1437 -1444
Sperandio V., Torres A. G., Jarvis B., Nataro J. P., and Kaper J. B. Bacteria-host communication: the language of hormones Proc. Natl. Acad. Sci. USA 2003 100 8951 -8956
Stein D. R., Allen D. T., Perry E. B., Bruner J. C., Gates K. W., Rehberger T. G., Mertz K., Jones D., and Spicer L. J. Effects of feeding Propionibacteria on dry cows on milk yield, milk components, and reproduction J. Dairy Sci. 2006 89 111 -125
Stephens T. P., Loneragan G. H., Chichester L. M., and Brashears M. M. Prevalence and enumeration of Escherichia coli O157 in steers receiving various strains of Lactobacillus-based direct-fed microbials J. Food Prot. 2007a 70 1252 -1255
Stephens T. P., Loneragan G. H., Karunasena E., and Brashears M. M. Reduction of Escherichia coli O157 and Salmonella in feces and on hides of feedlot cattle using various doses of a direct-fed microbial J. Food Prot. 2007b 70 2386 -2391
Stewart C. S., Flint H. J., and Bryant M. P. Hobson P. N. and Stewart C. S. The rumen bacteria The rumen microbial ecosystem 1997 2nd ed. London, UK Blackie Academic and Professional 10 -72
Szabo I., Wieler L. H., Tedin K., Sharek-Tedin L., Taras D., Hensel A., Appel B., and Noeckler K. Influence of a probiotic strain of Enterococcus faecium on Salmonella enterica serovar Typhimurium DT104 infection in a porcine animal infection model Appl. Environ. Microbiol. 2009 75 2621 -2628
Tabe E. S., Olya J., Doetkott D. K., Bauer M. L., Gibbs P. S., and Khaitsa M. L. Comparative effect of direct-fed microbials on fecal shedding of Escherichia coli O157:H7 and Salmonella in naturally infected feedlot cattle J. Food Protect. 2008 71 539 -544
Thrune M., Bach A., Ruiz-Moreno M., Stern M., and Linn J. Effects of Saccharomyces cerevisiae on ruminal pH and microbial fermentation in dairy cows yeast supplementation on rumen fermentation Livest. Sci. 2009 124 261 -265
Twomey D., Ross R. P., Ryan M., Meaney B., and Hill C. Lantibiotics produced by lactic acid bacteria: structure, function and application A. Van. Leeuw. 2002 82 165 -185
Vasconcelos J. T., Elam N. A., Brashears M. M., and Galyean M. L. Effects of increasing dose of live cultures of Lactobacillus acidophilus (Strain NP 51) combined with a single dose of Propionibacerium freudenreichii (Strain NP 24) on performance and carcass characteristics of finishing beef steers J. Anim. Sci. 2008 86 756 -762
Vermeiren L., Devlieghere F., Vandekinderen I., and Debevere J. The interaction of the non-bacteriocinogenic Lactobacillus sakei 10A and lactocin S producing Lactobacillus sakei 148 towards Listeria monocytogenes on a model cooked ham Food Microbiol. 2006 23 511 -518
von Buenau R., Jaekel L., Schubotz E., Schwarz S., Stroff T., and Krueger M. Escherichia coli Strain Nissle 1917: Significant reduction of neonatal calf diarrhea J. Dairy Sci. 2005 88 317 -323
Weiss W. P., Wyatt D. J., and McKelvey T. R. Effect of feeding propionibacteria on milk production by early lactation dairy cows J. Dairy Sci. 2008 91 646 -652
Wells J. E., Krause D. O., Callaway T. R., and Russell J. B. A bacteriocin-mediated antagonism by ruminal lactobacilli against Streptococcus bovis FEMS Microbiol. Ecol. 1997 22 237 -243
West J. W., Bernard J. K., Cross G. H., and Trammell D. S. Effect of live bacterial inoculants on performance of lactating dairy cows J. Dairy Sci. 2005 88 Suppl. 1 59
Whitford M. F., McPherson M. A., Forster R. J., and Teather R. M. Identification of bacteriocin-like inhibitors from rumen Streptococcus spp., and isolation and characterization of bovicin 255 Appl. Environ. Microbiol. 2001a 67 569 -574
Whitford M. F., Yanke L. J., Forster R. J., and Teather R. M. Lachnobacterium bovis gen. nov., sp. nov., a novel bacterium isolated from the rumen and faeces of cattle Int. J. Syst. Evol. Microbiol. 2001b 51 1977 -1981
Wiedmeier R. D., Arambel M. J., and Walters J. L. Effect of yeast culture and Aspergillus oryzae fermentation extract on ruminal characteristics and nutrient digestibility J. Dairy Sci. 1987 70 2063 -2068
Williams P. E., Tait C. A., Innes G. M., and Newbold C. J. Effects of the inclusion of yeast culture (Saccharomyces cerevisiae plus growth medium) in the diet of dairy cows on milk yield and forage degradation and fermentation patterns in the rumen of steers J. Anim. Sci. 1991 69 3016 -3026
Wiryawan K. G. and Brooker J. D. Probiotic control of lactate accumulation in acutely grain-fed sheep Aust. J. Agric. Res. 1995 46 1555 -1568
Yang J., Hou X., Mir P. S., and McAllister T. A. Anti-Escherichia coli O157:H7 activity of free fatty acids under varying pH Can J. Microbiol. 2010 56 263 -267
Yasuda K., Hashikawa S., Sakamoto H., Tomita Y., Shibata S., and Fukata T. A new synbiotic consisting of Lactobacillus casei subsp. casei and dextran improves milk production in Holstein dairy cows J. Vet. Med. Sci. 2007 69 205 -209
Yoon I. K. and Stern M. D. Influence of direct-fed microbials on ruminal microbial fermentation and performance of ruminants: A review Asian Australas. J. Anim. Sci. 1995 8 533 -555
Younts-Dahl S. M., Galyean M. L., Loneragan G. H., Elam N. A., and Brashears M. M. Dietary supplementation with Lactobacillus- and Propionibacterium-based direct-fed microbials and prevalence of Escherichia coli O157 in beef feedlot cattle and on hides at harvest J. Food Prot. 2004 67 889 -893
Younts-Dahl S. M., Osborn G. D., Galyean M. L., Rivera J. D., Loneragan G. H., and Brashears M. M. Reduction of Escherichia coli O157 in finishing beef cattle by various doses of Lactobacillus acidophilus in direct-fed microbials J. Food Prot. 2005 68 6 -10
Zhang W., Azevedo M. S. P., Gonzalez A. M., Saif L. J., Van Nuyen T., Wen K., Yousef A. E., and Yuan L. Influence of probiotic lactobacilli colonization on neonatal B cell responses in a gnotobiotic pig model of human rotavirus infection and disease Vet. Immunol. Immunopathol. 2008 122 175 -181
Zhao T., Tkalcic S., Doyle M. P., Harmon B. G., Brown C. A., and Zhao P. Pathogenicity of enterohemorrhagic Escherichia coli in neonatal calves and evaluation of fecal shedding by treatment with probiotic Escherichia coli J. Food Prot. 2003 66 924 -930
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Published In
Canadian Journal of Animal Science
Volume 91 • Number 2 • June 2011
Pages: 193 - 211
History
Received: 29 May 2010
Accepted: 19 January 2011
Version of record online: 28 April 2011
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McAllisterT. A., BeaucheminK. A., AlazzehA. Y., BaahJ., TeatherR. M., and StanfordK.. 2011. Review: The use of direct fed microbials to mitigate pathogens and enhance production in cattle. Canadian Journal of Animal Science.
91(2): 193-211. https://doi.org/10.4141/cjas10047
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and
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on microbial communities during ensiling and aerobic spoilage of corn silage1
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129. In vitro
assessment of the factors that determine the activity of the rumen microbiota for further applications as inoculum
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131. Microbes in Foods and Feed Sector
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133. Direct-fed microbial supplementation influences the bacteria community composition of the gastrointestinal tract of pre- and post-weaned calves
134. Expanding behavior pattern sensitivity analysis with model selection and survival analysis
135. Dietary manipulation: a sustainable way to mitigate methane emissions from ruminants
136. Using ruminally protected and nonprotected active dried yeast as alternatives to antibiotics in finishing beef steers: growth performance, carcass traits, blood metabolites, and fecal Escherichia coli1
137. Saccharomyces cerevisiae var. boulardii CNCM I-1079 and Lactobacillus acidophilus BT1386 influence innate immune response and serum levels of acute-phase proteins during weaning in Holstein calves
138. Probiotics and Ruminant Health
139. Use of a live yeast strain of Saccharomyces cerevisiae in a high-concentrate diet fed to finishing Charolais bulls: effects on growth, slaughter performance, behavior, and rumen environment
140. Fatty acid profile and carcass traits of feedlot Nellore cattle fed crude glycerin and virginiamycin
141. Effects of a live yeast in natural-program finishing feedlot diets on growth performance, digestibility, carcass characteristics, and feeding behavior1
142. The First 30 Years of Shiga Toxin–Producing Escherichia coli in Cattle Production
143. Review: Enhancing gastrointestinal health in dairy cows
144. Impact of Saccharomyces cerevisiae boulardii CNCMI-1079 and Lactobacillus acidophilus BT1386 on total lactobacilli population in the gastrointestinal tract and colon histomorphology of Holstein dairy calves
145. Using probiotics to improve swine gut health and nutrient utilization
146. Impact of persistent and nonpersistent generic
Escherichia coli
and
Salmonella
sp. recovered from a beef packing plant on biofilm formation by
E. coli
O157
147. Comparison of non-encapsulated and encapsulated active dried yeast on ruminal pH and fermentation, and site and extent of feed digestion in beef heifers fed high-grain diets
148. Changes in the relative population size of selected ruminal bacteria following an induced episode of acidosis in beef heifers receiving viable and non-viable active dried yeast
149. Effects of bacterial direct-fed microbials on ruminal characteristics, methane emission, and milk fatty acid composition in cows fed high- or low-starch diets
150. Impact of strain and dose of lactic acid bacteria on in vitro ruminal fermentation with varying media pH levels and feed substrates
151. Effects of Direct-Fed Microbials on Feed Intake, Milk Yield, Milk Composition, Feed Conversion, and Health Condition of Dairy Cows
152. Current Interventions for Controlling Pathogenic Escherichia coli
153. Effects of dietary active dried yeast (Saccharomyces cerevisiae) supply at two levels of concentrate on energy and nitrogen utilisation and methane emissions of lactating dairy cows
154. Methane and nitrous oxide emissions from Canadian dairy farms and mitigation options: An updated review
155. Bacteriocins: Recent Trends and Potential Applications
156. Effect of Direct-Fed Microbial Dosage on the Fecal Concentrations of Enterohemorrhagic
Escherichia coli
in Feedlot Cattle
157. Direct-Fed Microbial: Beneficial Applications, Modes of Action and
Prospects as a Safe Tool for Enhancing Ruminant Production and
Safeguarding Health
158. Screening of bacterial direct-fed microbials for their antimethanogenic potential in vitro and assessment of their effect on ruminal fermentation and microbial profiles in sheep1
159. Feeding wet distillers grains plus solubles with and without a direct-fed microbial to determine performance, carcass characteristics, and fecal shedding of Escherichia coli O157:H7 in feedlot heifers1
160. Feeding subtherapeutic antimicrobials to low-risk cattle does not confer consistent performance benefits
161. Using organic acids to control subacute ruminal acidosis and fermentation in feedlot cattle fed a high-grain diet1,2
162. Impact of adding Saccharomyces strains on fermentation, aerobic stability, nutritive value, and select lactobacilli populations in corn silage1
163. Modulation of the rumen microbiome
164. Evaluation of nutritional and economic feed values of spent coffee grounds and
Artemisia princeps
residues as a ruminant feed using
in vitro
ruminal fermentation
165. Effect of Propionibacterium freudenreichii on ruminal fermentation patterns, methane production and lipid biohydrogenation of beef finishing diets containing flaxseed oil in a rumen simulation technique
166. Use of a direct-fed microbial product as a supplement during the transition period in dairy cattle
167. Identification of lactic acid bacteria in the rumen and feces of dairy cows fed total mixed ration silage to assess the survival of silage bacteria in the gut
168. Bacteria, phages and pigs: the effects of in-feed antibiotics on the microbiome at different gut locations
169. Supplementing
Propionibacterium acidipropionici
P169 does not affect methane production or volatile fatty acid profiles of different diets in
in vitro
rumen cultures from heifers
170. The Protective Effects of Probiotics on High Fat Diet-Induced Oxidative Damage Using a Comet Assay in Rats
171. Effect of Propionibacterium acidipropionici P169 on growth performance and rumen metabolism of beef cattle fed a corn- and corn dried distillers’ grains with solubles-based finishing diet
172. Effect of Propionibacterium spp. on ruminal fermentation, nutrient digestibility, and methane emissions in beef heifers fed a high-forage diet1
173. A Mixture of Lactobacillus casei, Lactobacillus lactis, and Paenibacillus polymyxa Reduces Escherichia coli O157:H7 in Finishing Feedlot Cattle
174. The effects of active dried and killed dried yeast on subacute ruminal acidosis, ruminal fermentation, and nutrient digestibility in beef heifers1
175. The use of direct-fed microbials for mitigation of ruminant methane emissions: a review
176. Effects of Propionibacterium strains on ruminal fermentation, nutrient digestibility and methane emissions in beef cattle fed a corn grain finishing diet
177. Effects of a Bacteria-Based Probiotic on Subpopulations of Peripheral Leukocytes and Their Cytokine mRNA Expression in Calves
178. Evaluation of a shelf-stable direct-fed microbial for control of Escherichia coli O157 in commercial feedlot cattle
179. Portage des Escherichia coli entérohémorragiques par les ruminants et effet de probiotiques
180. Using strains of Propionibacteria to mitigate methane emissions
in vitro
181. Survival of silage lactic acid bacteria in the goat gastrointestinal tract as determined by denaturing gradient gel electrophoresis
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