Rumen additives

Vitamins such as thiamin, biotin, and vitamin Bj2 are often added. Once again, the requirements of anaerobes are somewhat greater, and a more extensive range of vitamins that includes pantothenate, folate, and nicotinate is generally employed. In some cases, additions of low concentrations of peptones, yeast extract, casamino acids or rumen fluid may be used, though in higher concentrations, metabolic ambiguities may be introduced since these compounds may serve as additional carbon sources. 

Finally, the contents of the omasum, now a thick slurry of microorganisms, pass into the abomasum into which are secreted acid and proteinases to produce an environment corresponding to that of the human stomach. Some of the microflora passing from the rumen to the omasum die and are digested by the acid and the enzymes. This provides the ruminant not only with an additional energy source but with vitamins and essential amino acids that its own tissues caimot synthesise. 

A low cobalt concentration was shown by Hendlin and Ruger (1950) to limit synthesis of vitamin Bi2. Cobalt comprises about 4% of the molecule. Working with 13 cultures, including a strain of Streptomyces griseus, unidentified rumen and soil isolates, a strain of Mycobacterium smegmatis, and Pseudomonas species, Hendlin and Ruger (1950) found that addition of 1 to 2 ppm of cobalt increased yield by threefold. 

In vitro rumen fermentation of the heated alfalfas showed (Table V) a decrease in organic matter digestibility (OMD) which was of the same order of magnitude as the increase in NDIN, suggesting that the NDIN fraction was resistant to microbial attack at rumen pH (6.9). The addition of HCl-pepsin to give a pH of... 

Physical or chemical modification of a substrate may additionally selectively affect transformation or uptake Keil and Kirchman (1992) compared the degradation of Rubisco uniformly labeled with 3H amino acids produced via in vitro translation to Rubisco that was reductively methylated with 3H-methane. Although both Rubisco preparations were hydrolyzed to lower molecular weights at approximately the same rate, little of the methylated protein was assimilated or respired. The presence of one substrate may also inhibit uptake of another, as has been demonstrated for anaerobic rumen bacteria. Transport and metabolism of the monosaccharides xylose and arabinose were strongly reduced in Ruminococcus albus in the presence of cellobiose (a disaccharide of glucose), likely because of repression of pentose utilization in the presence of the disaccharide. Glucose, in contrast, competitively inhibited xylose transport and showed noncompetitive inhibition of arabinose transport, likely because of inactivation of arabinose permease (Thurston et al., 1994). 

In addition to 02 and C02, N2, H2 and CH4 are found in various concentrations in different vertebrates and these gases make up 99% of the intestinal gas in man. The source of H2 and CH4 appears to be bacterial metabolism and, in cattle rumen, CH4 is known to be produced by Methanobacterium rumentium. The composition and origin of intestinal gas in man has been reviewed in detail by Levitt et at. (444). 

Information on the effect of diet on the production of minor isomers of CLA in the rumen and alterations in their content in milk fat is limited. Diet-induced changes in trans-10, cis-12 CLA have been best described, and its biological effects in the dairy cow will be discussed in Section 3.6.1. Griinari and Bauman (1999) presented a putative pathway for the biohydrogenation of linoleic acid where the initial isomerization involved the cis-9 double bond, thereby resulting in the production of trans-10, cis-12 CLA and trans-10 18 1 as intermediates. As discussed earlier, rumen bacteria have been identified that produce trans-10, cis-12 CLA when incubated with linoleic acid (Verhulst et al., 1987 Kim et al., 2002), and the addition of trans-10, civ-12 CLA to the rumen results in the increased formation of trans-10 18 1 (Loor and Herbein, 2001). 

Fatty acids are the building blocks of TAG. More than 90 percent of fatty acids have an even number of carbon atoms, and are in aliphatic chains ranging from 4 to 22 carbons in length. The major fatty acid synthesis pathway is production of stearic acid (18 carbons) after which separate desaturase systems introduce 1, 2, or 3 unsaturated (double) bonds. Additional enzymes become active in elongating the chain as needed. Shorter fatty acids also are produced. Trace amounts of odd-number carbon fatty acids are found in most fats, and also have been synthesized for research purposes. Microorganisms frequently produce odd-number carbon fatty acids, with heptadecenoic (17 carbon) acid a major component of Candida tropicalis yeast fat. Up to 8 percent C17 fatty acids have been found in milk and meat fats of ruminants (cattle, sheep, goats) and are of rumen microbe origin. 

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