The effect of fish oil supplementation on rumen metabolism and the biohydrogenation of unsaturated fatty acids in beef steers given diets containing sunflower oil

Duodenally and ruminally fi stulated steers were offered grass silage and one of three concentrates at a ratio of 60 : 40 (forage : concentrate on a dry-matter basis) : F0, F1 or F4 at 14 g/kg live weight. The concentrates were designed to be iso-lipid and to provide the same amount of sunfl ower oil but increasing amounts of fi sh oil : 0, 1 and 4 g per 100 g, respectively. Ruminal characteristics were measured along with fatty acid intakes and duodenal fl ows to determine the effect of fi sh oil on : ruminal pH, ammonia-N concentration, volatile fatty acid ( VFA) concentration and polyunsaturated fatty acid ( PUFA) metabolism. Fish oil had no signifi cant effect on ruminal pH, ammonia-N concentration or the molar proportions of the major VFA, although total VFA concentration was signifi cantly reduced at the highest level of fi sh oil inclusion. Fish oil signifi cantly increased the fl ow of long chain PUFA, total conjugated linoleic acid and vaccenic acid to the duodenum and decreased the fl ow of stearic acid. Biohydrogenation, as determined by the net loss of fatty acid between the mouth and duodenum, of oleic and linolenic acid was not affected by fi sh oil inclusion and averaged 0·64 and 0·92, respectively. There was a small increase in the biohydrogenation of linoleic acid with increasing fi sh oil from 0·89 to 0·92 ( P