Effects of high-forage content and oilseed supplementation of fattening diets on conjugated linoleic acid (CLA) and trans fatty acids profiles of beef lipid fractions.

Two experiments were conducted to study the effects of forage level and oilseed supplementation of fattening diets on the composition of fatty acids (FA), including C18:1 trans FA and conjugated linoleic acid (CLA), in lipid fractions of the meat. In experiment 1, 48 Friesian bull calves were fed high or low forage diets, either supplemented, or not, with crushed raw flax, for 300 days until slaughter. A factorial design of four dietary treatments was used. In experiment 2, 48 calves were fed high or low forage diets, supplemented with either crushed raw soybean or flax for 180 days until slaughter. Slices of the longissimus muscle between the 12th and 13th ribs were sampled from all calves and analysed for fatty acid composition of intra-muscular fat in experiments 1 and 2, and of subcutaneous fat in experiment 2. The intra-muscular fat content in experiment 1 was higher (57 g/kg of fresh weight) in calves fed on the low forage, flax-supplemented diet versus the other diets (less then 50 g/kg). The intra-muscular fat content in experiment 2 was higher (50 g/kg fresh weight) on the low forage diets versus the high-forage diets (40 g/kg). The CLA and C18:1 trans FA contents were higher in subcutaneous versus intra-muscular fat. Supplementation of diets with flax increased the contents of these FA in both lipid fractions, but this increase was small on low forage diets and larger on high-forage diets. No increase of CLA and C18:1 trans FA in the meat lipid fractions versus values usually obtained on standard finishing diets could be detected by supplementation of either low or high-forage diets with crushed raw soybeans.