Influence of host diet on the concentrations of fatty acids in rumen bacteria from cattle

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Abstract
This study compared the effects of supplements (300 mL/day) of safflower oil (SO) on the long-chain fatty acid (LCFA) content and composition of rumen liquid-associated (LAB) and solid-associated bacteria (SAB) in two experiments: (1) Hereford steers fed lucerne hay (6 kg/day) and (2) Brahman steers fed low-quality hay (4 kg/day). Experiment 1: SO increased the concentrations of mono-unsaturated (MUFA) and polyunsaturated acids (PUFA) in bacteria without altering the concentrations of saturated acids (SFA). The concentrations of all classes of LCFA except PUFA were higher in SAB than in LAB. Variation in phospholidpid (PL) composition of bacteria in response to SO included lowered proportions of branched-chain (brFA) and odd-numbered acids. In steers fed hay alone, the neutral lipids (NL) of all bacteria consisted predominantly of SFA (90%). With SO supplement, SFA constituted 60% and trans-11 monoenoic acid 31% of NL. There were significant differences between LAB and SAB in the proportions of individual acids in PL and NL. Experiment 2: SO increased the concentrations of all classes of LCFA except brFA which were decreased. SO treatment decreased the proportions of all acids in NL, except 18: 0, 18 : 1 trans-1 1 and 18 : 2, which were increased. The results have demonstrated that the fatty acid content and composition of mixed rumen bacteria is dependent upon their nutrient supply.
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