Rumen flora

When planning for Tilley and Terry digestibilities, it is common practice to ensure that the sheep or cattle have been fed for a couple of weeks on a basal diet similar to the test samples to be analysed. This is to ensure a buildup of the appropriate rumen flora resulting in a corresponding optimal activity. Whether or not this is necessary is open to question, and this and other sources of error have been discussed by Ayres (1991). It is also customary not to feed the animal on the morning planned for extracting the rumen liquor. 

Cyanocobalamin (vitamin B12), a cobalt complex first isolated from liver but now produced commercially from microbiological culture, is needed to maintain normal synthesis of red blood cells in man and animals. Ruminants obtain cyanocobalamin from their symbiotic rumen flora while in other herbivores such as the... 

Paraoxon is the toxic metabolite produced in animals, whereas diethyl-phosphorothionate is a detoxication product. Microorganisms may, under anaerobic conditions, produce amino-parathion, which has a much lower animal toxicity than parathion. Therefore, parathion by oral administration is less toxic to ruminants than to other mammals. The highly active rumen flora detoxicates parathion by reducing it to amino-parathion. However, parathion deposited on leaves or dust particles can absorb light energy and be isomerized to iso-parathion, which has a high animal toxicity. 

OH)2D2-degradatlon products from rat blle,32 and the lO-oxo-19-nor-5,6-trans-dervlatlve of D2, D, and 25-OH-D2 (structures not shown) resulting from the Incubation of bovine rumen flora with the respective... 

But where do all the other isomers come from Desaturation should not occur in the reducing environment of the rumen and thus could not explain the array of isomers observed as desaturation of rra r-monoenes. On the other hand, hydrogenation is efficiently accomplished when rumen pH is appropriate for the organisms involved in the isomerization and hydrogenation of PUFA (16). Several of the organisms appear to have specific selectivity for certain structures of the PUFA on which they act. Different microbes could have different preferences for PUFA isomers, rumen pH, or nutrients but there is insufficient information at this time to clearly describe the rumen flora in a way that would explain the plethora of fatty acid isomers observed in the rumen and milk of dairy cows. The following discussion may provide insights into possible mechanisms to explain the presence of the myriad of trans, cis, and CLA fatty acids in rumen and milk fat. 

It is probable that the relative contributions of diet and biosynthesis to taurine regulation varies from species to species. Taurine is almost absent from the plant kingdom, but is present in large amounts in animal tissues, particularly muscle. A carnivore, therefore, receives a large amount of taurine in its diet, whereas a herbivore receives none. Omnivores fall between these two extremes. A herbivore must either make its own taurine, or derive it microbiologically from gut or rumen flora. A carnivore is not faced with this necessity, and, as the example of the cat shows, biosynthesis may be insufficient to maintain taurine balance. 

Desaturation of an acyl chain is a reaction widespread in Nature. The reverse process, namely the hydrogenation of double bonds, is found in only a few organisms. These organisms are commonly found in the rumens of cows, sheep and other ruminant animals. Linoleic acid, for example, can be hydrogenated by rumen flora (anaerobic bacteria and protozoa) to stearic acid by the series of reactions shown in Figure 3.15. 

The primary fate of dietary fibers is digestion and catabolism by the gut microflora to short-chain fatty acids and carbon dioxide. The major products of this microbiai mctaboiism — acetic, propionic, and butyTic acid — are important sources of energy for ruminants (sheeps cows). Dietary fiber is retained in a chamber of their gastrointeslinai tracts, calied the rumen, where it is converted to short-chain fatty acids by the gut micro flora. The fatty acids produced may supply 3 75 y<> of the energy requirement of the ruminant. 

Nitrates are reduced to nitrites by rumen micro-flora. In normal circumstances the nitrite ion is rapidly utilized for ammonia synthesis, but in cases of excessive acute intake of nitrate, the rapidly formed nitrite ion is absorbed into the bloodstream. In blood... 

Since the first scientific explanation of the favorable effects of soured milk products in humans by Metchnikoff (1907) at the beginning of the twentieth century, the most beneficial part of the intestinal flora is suggested to be LAB. LAB are also the most common organisms used for commercial DFM preparations (Anonymous, 1990 Tuschy, 1986). The emphasis on the LAB stems from evidence that LAB play a central role in the gut flora that enables them to influence the composition of the flora to the benefits of the host. The stomach of the neonatal pigs is shown to be colonized by Lactobacillus and Streptococci within 48 hours after birth (Dulcuzeau, 1985). Similarly, in newborn calves one of the first groups of microorganisms in the rumen is LAB (Nousiainen and Setala, 1993). Studies show that when the gut flora develops after birth, as the lactobacilli increase, other components of the flora decrease (Smith, 1965). The claims made for DFM effects of LAB in farm animals are many and varied. 

Feedlot cattle have been fed ionophores for decades to alter rumen microbial flora and to improve feed conversions (Russell and Houlihan, 2003), and an early study observed a tendency for increased . coli 0157 herd prevalence when ionophores were fed (Herriott et al, 1998). Grampositive bacteria are more sensitive to ionophores (Russell and Houlihan, 2003), and commonly fed ionophores, such as monensin or lasalocid, have little effect on the Gram-negative E. coli 0157 H7 in pure culture studies (Bach et al, 2002b Edrington et al, 2003). In feedlot studies with cattle fed grain diets, neither monensin or tylosin altered . coli 0157 H7 fecal prevalence (Jacob et al, 2008b McAllister et ah,... 

Toxicity can result from excess dietary sulphur, which is converted to hydrogen sulphide, a toxic agent, by the gastrointestinal flora. This reduces rumen motility and causes nervous and respiratory distress. 

In addition to improved, growth responses in young rats, birds, and pigs, it is claimed that supplementing the diet with an antibiotic benefits young calves. As the commensal microorganisms of the rumen play an important role in older animals, it is not unexpected to find evidence that an antibiotic such as aureomycin interferes with the pattern of the normal flora sufficiently to alter the course of microbial digestion in these older animals. ... 

When considering sources of niacin, it should be noted that niacin can be, and is, synthesized by the intestinal flora. However, the amount produced is only of minor importance in the human. By contrast, as with thiamin and riboflavin, ruminants (cattle, sheep, etc.) have no dietary requirements for niacin because of bacterial synthesis in the rumen. 

Cellulases are commonly found in microorganisms, but rarely in animals. The utilization of cellulose almost invariably requires the participation of the microbial flora (e.g. in the rumen of ruminants). 

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