Linseed oil supplementation of the diet of sheep: effect on the in vitro fermentation of amino acids and proteins by rumen microorganisms

Abstract

The effects of addition of 6% linseed oil (LSO) to the diet of three sheep on short-term in vitro fermentation of cellobiose + maltose, aspartic acid, glutamine, threonine, casein and ovalbumin by rumen microorganisms were studied. The addition of LSO to the diet significantly lowered the mean number of protozoa in the rumen of sheep used as donors from 5.7 × 10 5 ml −1 to 1.9 × 10 5 ml −1 ( P < 0.05). Linseed oil supplementation did not modify the amounts of theoretical fermented hexose in the cellobiose-maltose incubations but decreased by 44% the molar proportion of butyrate ( P < 0.05). Linseed oil lowered the degradation of all the amino acids, but the decrease was significant only for glutamine (51%, P < 0.05). The addition of LSO tended to lower the production of volatile fatty acids (VFA) and decreased the production of ammonia by 58% ( P < 0.05) in ovalbumin fermentation while its effects on casein incubation were very slight. The amount of methane derived from amino acid fermentation was very low and was not modified by LSO, but LSO supplementation induced a fall of 40% in the amount of methane derived from the basal constituents of rumen juice. Methanogenesis was strongly inhibited by LSO in both types of protein incubations ( P < 0.05). These effects of LSO supplementation could be related to the bibliographic results which point out the differences in sensitivity to polyunsaturated fatty acids between rumen bacteria.