1. Thirty Ayrshire bull calves were used in an experiment to study the effects of diets containing different proportions of concentrates to hay on rumen development at 12 weeks of age. In addition, six milk-fed calves were slaughtered at 3 weeks of age for comparison. 2. Restriction of the maximum daily allowance of concentrates to the lower levels was accompanied by an increase in the voluntary intake of hay, but the performance of calves from 3 to 12 weeks of age was significantly better in calves given the high-concentrate diets. 3. The weight of contents of the reticulo-rumen increased from 0.7 kg at 3 weeks of age in the milk-fed calf to 7.7 kg and 10.9 kg at 12 weeks in calves given the high-concentrate and high-roughage diets respectively. Between 68 and 79% of the total contents of the alimentary tract was contained in the reticulo-rumen of the ruminant calf. The weight of contents of the omasum was significantly greater in calves given 1.36 kg concentrates/day than in those given either 0.45 or 2.27 kg concentrates/day. Equations were developed from the results by which the weight of contents of the various parts of the alimentary tract, and hence empty body weight in the live animal, can be determined from a knowledge of the live weight and daily consumption of concentrates and hay, 4. Volume displacement of the reticulo-rumen tended to increase with increase in the proportion of hay in the diet. The volume displacement of the omasum increased in response to concentrate intake up to a maximum of 1.36 kg/day and thereafter declined, but the nature of the diet had no significant effect on the volume displacement of the abomasum. 5. Calves given the high-concentrate diets had a significantly greater weight of reticulo-rumen tissue at 12 weeks than those given the high-roughage diets. 6. Whereas the thickness of the muscular wall of the rumen did not differ significantly between treatments, there was an increase in the length and density of papillas, particularly in the anterior dorsal and ventral sacs of the rumen, as the intake of concentrates was increased. The results show the marked relationship between the performance of the animal and an advanced stage of development of the rumen papillas.

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Rumen development in the calf. 1. The effect of diets containing different proportions of concentrates to hay on rumen development.

The production and metabolism of volatile fatty acids by ruminants fed roughages: a review

Net production of isobutyric acid, isovaleric acid, and 2-methylbutyric acid by cultures of Bacteroides ruminicola and Megasphaera elsdenii on media that contained Trypticase or casein hydrolysate continued (up to 5 days) after growth had ceased Only trace quantities of these acids were produced in a medium that contained a mixture of amino acids that did not include the branched-chain amino acids M elsdenii produced increased quantities of the branched-chain fatty acids in a medium that contained Trypticase when glucose was reduced or eliminated from the culture medium However, B ruminicola produced increased quantities of branched-chain fatty acids and of phenylacetic acid from Trypticase when glucose was supplied at 3 mg/ml rather than at 1 mg/ml Single strains of Streptococcus bovis, Selenomonas ruminantium, Bacteroides amylophilus, and Butyrivibrio fibrisolvens did not produce branched-chain fatty acids

Production of branched-chain volatile fatty acids by certain anaerobic bacteria.

1. The concentrations of volatile fatty acids (VFA) in the rumen and caecum were compared when sheep were given barley or dried grass. The molar proportions of VFA in the caecum resembled those in the rumen except that the proportions of isobutyric and isovaleric acids were higher in caecal than in rumen fluid indicating an extensive breakdown of protein during fermentation in the caecum.2. The capacity for starch digestion in the large intestine was studied in two sheep receiving dried grass. Starch was infused into the caecum, the amount given increasing by daily increments of 20 g until 300 g daily were infused. Infused starch in excess of 138 g daily largely appeared in the faeces, indicating a limited but substantial capacity for starch fermentation in the large intestine. The infusion caused a marked increase in the molar proportion of butyric acid.3. Determinations made with a single sheep showed that the infusion of starch into the caecum caused large changes in the microflora, and species similar to Butyrivibrio became prevalent. The viable count on a starch medium was increased by 83 % by starch infusion.4. The infusions of starch increased the excretion of nitrogen in the faeces from 5.8 to 9.0 g daily. Using a fractionation procedure it was shown that when 100 g of starch were fermented in the large intestine the 'bacterial and endogenous debris' nitrogen increased by about 1.0 g. When starch was given orally to two sheep the increase in this fraction was about 0.4g nitrogen/100 g starch digested.5. It is suggested that dietary factors that cause changes in the site of fermentation from the rumen to the caecum will render less microbial nitrogen available to the host animal per unit of carbohydrate fermented and decrease the apparent digestibility of nitrogen.

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Influence of starch digestion in the large intestine of sheep on caecal fermentation, caecal microflora and faecal nitrogen excretion.

Allison, M. J. (Dairy Cattle Research Branch, USDA, Beltsville, Md.), M. P. Bryant, I. Katz, and M. Keeney. Metabolic function of branched-chain volatile fatty acids, growth factors for ruminococci. II. Biosynthesis of higher branched-chain fatty acids and aldehydes. J. Bacteriol. 83:1084-1093. 1962.-A number of strains of rumen bacteria require branched-chain volatile fatty acids for growth. A strain of Ruminococcus flavefaciens that requires either isovalerate or isobutyrate incorporates radioactive carbon from isovalerate-1-C(14) and isovalerate-3-C(14) into leucine and into the lipid fraction of the cells. Evidence obtained by both paper and gas chromatography indicated that most of the label in the lipid of cells grown in isovalerate-1-C(14) was in a branched-chain 15-carbon fatty acid, with some in a 17-carbon acid; about 7.5% of the C(14) was recovered in a branched-chain 15-carbon aldehyde. The aldehydes were in the phospholipid fraction and were presumably present as plasmalogen.A strain of R. albus was shown to require isobutyrate, 2-methyl-n-butyrate, or 2-ketoisovalerate for growth. This strain did not incorporate appreciable C(14) from isovalerate-1-C(14) or isovalerate-3-C(14). When grown in a medium containing isobutyrate-1-C(14), most of the cellular C(14) was found in the lipid fraction. Analysis of the lipid demonstrated that the label was present mainly as branched-chain 14-carbon and 16-carbon fatty acids, with 11% of the C(14) present in 14- and 16-carbon carbonyl compounds, presumably branched-chain aldehydes.Branched-chain 14-, 15-, and 16-carbon fatty acids are major components of the lipids of these rumen bacteria. The possibility that these acids and aldehydes, which are found in ruminant body and milk lipids, may be of microbial origin is discussed.

Metabolic function of branched-chain volatile fatty acids, growth factors for ruminococci. II. Biosynthesis of higher branched-chain fatty acids and aldehydes.

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Some observations on volatile fatty acids in the sheep's rumen.

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E. F. Annison

Papers

Some observations on volatile fatty acids in the sheep's rumen.

The metabolism of short-chain fatty acids in the sheep. 3. Formic, n-valeric and some branched-chain acids