Changes in the rumen metabolism of sheep given increasing amounts of linseed oil in their diet

Abstract

I . Linseed oil was incorporated gradually into the diet of four sheep until the animals received 90 g additional fat/d. Attempts were made to measure changes in concentration of substances and rates of synthesis in the rumen directly, and by incubation of rumen contents in vitro (zero-time technique).2 . The high-fat diet increased the dilution rate and the volume of rumen contents and decreased the synthesis of diaminopimelic acid in the rumen. The number of protozoa decreased and the number of bacteria increased in the rumen of animals receiving the high-fat diet.3. The concentration of volatile fatty acids (VFA) in the rumen decreased for sheep given the high-fat diet, but the capacity of rumen contents to produce VFA in vitro increased.4. The incorporation of radioactivity from [14C]acetate into lipids during incubation of rumen contents in vitro increased with the amount of linseed oil in the diet. The greatest proportional increase was with the bacterial fraction of rumen contents.5. In the group of four animals used, one animal showed consistent differences in the magnitude of the measured variables. This animal appeared to have a smaller rumen, a lower dilution rate and larger concentrations of some substances in the rumen. A higher proportion of fatty acids appeared to be synthesized by the micro-organisms from this animal. (1972) found that the net lipid synthesis was greater with high-fat diets. In our earlier work (Czerkawski, 1966) when the intake of linseed-oil fatty acids was increased gradually to a level that constituted 18 % of the total energy content of the diet, there was inhibition of methane production, a small increase in faecal excretion of cellulose and crude lipid, but no change in faecal excretion of nitrogen. Further experiments in which linseed-oil fatty acids or linseed oil were added to the diet of sheep in increasing amounts (Czerkawski, 1973), showed that the changes in the fermentation patterns were similar for all sheep, but in some, lipid metabolism in the rumen appeared abnormal in as much as there was considerable accumulation of palmitic acid and smaller amounts of myristic acid. It was concluded on the basis of these experiments that the increases in concentration of palmitic acid were due to the increased synthesis of this compound in the rumen, and an indirect estimate of the magnitude of this synthesis was made. The value was similar to those obtained by direct measurements reported by other workers. However, there were a number of puzzling features. For instance, the changes in fermentation pattern, such as inhibition of methane production, decreased concentration of acetate and butyrate in the rumen, or increased excretion of lipid in the faeces, occurred in all sheep irrespective of whether there was a large synthesis of palmitic acid or not. It was suggested that the increase in lipid synthesis occurred in all sheep, but in those sheep that had unchanged concentrations of palmitic acid, other fatty acids and possibly more complex lipids were being synthesized. I...

Digestion of fatty acids in ruminants: a meta-analysis of flows and variation factors. 1. Total fatty acids

“…Moreover, it is generally assumed that de novo synthesis of bacterial lipids decreases when the amount of exogenous lipids increases (Doreau and Ferlay, 1994). Indeed, ruminal bacteria can reduce the de novo synthesis of FA in high-fat diets both in vitro (Demeyer et al, 1978) and in vivo (Czerkawski et al, 1975), which suggests a preferential utilization of preformed FA rather than synthesis of FA, which could be considered as an energy-sparing process since direct incorporation of FA demands less energy than synthesis (Demeyer and Van Nevel, 1995).…”

Distribution and changes in urease (EC3.5.1.5) activity in Rumen Simulation Technique (Rusitec)

“…The incubations were carried out in Rusitec as described by Czerkawski & Breckenridge (1977). The gases were analysed as described by Czerkawski & Clapperton (1968) and the volatile fatty acids (VFA) as described by Czerkawski (1976), using pivalic acid as internal standard.…”

“…The concentrations of ammonia were determined with the same reagents as used for the urease assays. The protozoal and bacterial counts were made as described by Czerkawski et al (1975).…”

“…The Rumen Simulation Technique (Rusitec) is a simple but reliable model system that can be used to study rumen fermentation under controlled conditions (Czerkawski & Breckenridge, 1977). Rusitec has considerable practical potential (e.g.…”

Influence of the presence of protozoa on the rumen microbial population of cattle.

“…The first method consists of separating young animals from their dam after birth and preventing all contact with faunated ruminants (2). The second method necessitates the use of specific chemicals to eliminate protozoa in the rumen (1,3,9). The third method consists of emptying the rumen, treating the rumen contents by freezing and thawing to destroy protozoa, and reintroducing the treated rumen contents into the rumen (11).…”