Rumen microflora

The requirements of dairy cattle for B-vitamins, determined almost half a century ago, concluded that a ruminant animal does not require an exogenous supply of B-vitamins because its rumen microflora should synthesise enough of these compounds to avoid deficiency. Since then, dairy cows have greatly increased their average milk and milk component yields. More recent studies have shown that B-vitamin supply in dairy cows is increased by supplementation, although losses in the rumen are extensive (Santschi et al., 2005). Whilst there are few reports of B-vitamin supplementation affecting milk quality, supplemental biotin has been shown to directly improve milk yield (Majee et al., 2003). 

In most species, chloramphenicol is rapidly and almost completely absorbed from the gastrointestinal tract. This route of administration provides antibiotic levels in blood comparable witli or higher than die intramuscular or the subcutaneous routes. The only known exception is in ruminants in which the drug is destroyed by the rumen microflora. 

Lactones are cyclic compounds formed through the intramolecular esterification of a hydroxy fatty acid. 7-Lactones and 8-lactones, with fivesided and six-sided rings, respectively have been found in cheese (Jolly and Kosikowski, 1975 Wong et al., 1975 Collins et al., 2004). The origin of the precursor hydroxy fatty acids has been ascribed to a 8-oxidation system in the mammary gland of ruminants (see Fox et al., 2000), the reduction of keto acids (Wong et al., 1975) and/or the action of lipoxygenases and other enzymes present in members of the rumen microflora (Dufosse et al., 1994). Lactones have low flavor thresholds and while their aromas are not specifically cheese-like (their aromas have been described variously as peach, apricot and coconut ), they may contribute to the overall flavor of cheese (see Collins et al., 2004). 

The carbonyl compounds formed due to autoxidation of lipids and in catabolic processes postmortem in muscles, or introduced with wood smoke, can bring about undesirable effects by interacting with a.a. residues. On the other hand, some carbonyl compounds are used intentionally to modify the proteins. Formaldehyde can harden the collagen dope in the manufacturing of sausage casings, protect fodder meals against deamination by the rumen microflora, and bind immobilized enzymes on supports. 

Although cellulase activity of rumen microflora is high, lignocellulose feed stuffs are only partially degraded that is, only part of the potential energy is made available for animal production. 

Cellulose is usually the most abundant polysaccharide of the cell wall constituents and the most insoluble. It is a polymer of glucose units and the degree of polymerization varies within and between sources of cellulose (38). In most isolation procedures employed for nutrition studies some polymers of xylose are included with the cellulose. Cellulose is available to the rumen microflora to a variable degree ranging from about 25 to 90%. 

Factors Affecting Cellulolytic Activity of Rumen Microflora... 

The aspen silage was extremely low in nitrogen (0.1% DM basis) so that nitrogen deficiency in the inoculum from animals fed this material was probably a major factor in reducing the cellulolytic activity of the rumen microflora. 

Cobalt, while essential at low levels for vitamin Bi2 synthesis and efficient functioning of rumen microflora, will depress cellulolytic activity of rumen microflora in vitro at levels of 12 p.p.m. and above (35). Selenium inhibited cellulose digestion in vitro at the 0.3 p.p.m. level (24). 

The fatty acid profile of ruminant fats (milk and adipose tissue) is relatively constant due to the buffering action of the rumen microflora that modify ingested lipids. However, the proportions of various fatty acids in milk lipids show seasonal/nutritional/lactational variations (Figure 3.5) which are reflected in seasonal variations in the hardness of milk fat (Figure 3.7). 

Fermentability using human fecal inoculum ranges from a high of 91% (cabbage) to a low of 0% (Maillard product) demonstrating the sensitivity of human microflora to different fiber sources. Fermentability of cellulose by human fecal microflora (23Z) is substantially less than rumen microflora (94%). The microflora in the human intestine may be more affected by fiber composition than rumen microflora. Work by Bryant (19) and Jeraci (11) leads to speculation that variation among inoculum sources in humans on a particular substrate could be greater than in other species. 

The absorption, distribution, metabolism and excretion of ochratoxin A have been summarized previously by the Committee as follows (Annex 1, reference 153). Ochratoxin A is efficiently absorbed from the gastrointestinal tract, mainly in the small intestine. Information from a number of species shows that it is distributed via the blood, mainly to the kidneys, with lower concentrations being found in liver, muscle and fat. Transfer to milk has been demonstrated in rats, rabbits and humans, but little is transferred to the milk of ruminants, owing to hydrolysis of ochratoxin A into phenylalanine and ochratoxin alpha by the rumenal microflora. The major metabolite of ochratoxin A in all species examined is ochratoxin alpha, formed by hydrolysis of the peptide bond. Ochratoxin alpha and minor hydroxylated metabolites that have been identified are all reported to be less toxic than ochratoxin A itself. Ochratoxin A is excreted in urine and faeces, and the relative contribution of each of these routes in different species is influenced by the extent of the... 

Cobalt is essential for animal nutrition, but it has not been established as essential for plant growth. Ruminant animals require cobalt for the synthesis of vitamin Bi2 by their rumen microflora. This was established about 1935, but an essential role of cobalt in plants was not demonstrated until 1960 [33]. Cobalt has been found to be essential for the growth of legumes which rely on symbiotic nitrogen fixation. 

Factors, other than diet, that may influence these large individual variations in CLA levels, have not been clarified adequately. However, tissue A -desaturase activity, and the viability of certain rumen microflora responsible for aspects of biohydrogenation may be contributing factors. 

Inorganic forms arsenic are more acutely toxic than the organic arsenicals and the toxicity depends upon the oxidation state of arsenic. Conversion between the oxidation states of inorganic arsenic have been shown to occur both in the environment and in the animal body. Recent studies (Vahter and Norin, 1980 Vahter, 1981) have suggested that the differences between the toxicities of trivalent and pentavalent arsenic depend upon the extent of vivo biotransformation to methylated metabolites. Environmental oxidation favors the conversion of trivalent arsenic to pentavalent arsenic. Pentavalent arsenic may be partially reduced vivo to trivalent arse-noxide (R As 0), but it is the vivo reduction of arsenate to arsenite which accounts for both toxicity and antimicrobial actions (Harvey, 1975). Rumen microflora obtained from Holstein cows reduced arsenate to arsenite (Forsberg, 1978). Ginsberg (1965) demon-... 

Forsberg, C. W., 1978, Some effects of arsenic on the rumen microflora An vitro study. Can. J. Microbiol., 24 36-44. 

The effect of essential oils and other compounds modulating fermentation processes in the rumen is determined by their influence on the inhabiting microflora. Qualitative (e.g. PCR-DGGE) or qualitative and quantitative techniques (e.g. Real-time PCR or FISH) seems to be very useful to assess changes of rumen microflora as the effect... 

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