Delta9 desaturase activity in bovine subcutaneous adipose tissue of different fatty acid composition

Two experiments were conducted to investigate the relationship between delta9 desaturase (stearoyl-coenzyme A desaturase) activity and fatty acid composition in subcutaneous adipose tissue from cattle of different backgrounds. In Experiment 1, subcutaneous adipose tissue samples were taken from carcasses of pasture-fed cattle and feedlot cattle fed for 100, 200, or 300 d. Adipose tissue from pasture-fed cattle had significantly lower total saturated fatty acids and higher total unsaturated fatty acids than feedlot cattle. Desaturase activity correspondingly was 60-85% higher in pasture-fed cattle than in feedlot cattle. There was no difference in the fatty acid composition or desaturase activity among samples from the 100-, 200-, and 300-d feedlot cattle. In Experiment 2, adipose tissue samples were collected from carcasses of feedlot cattle fed for 180 d with either a standard feedlot ration (control group), or a ration containing rumen-protected cottonseed oil (CSO) for the last 70-80 d. Adipose tissue from the CSO-fed cattle was more saturated than that from the control group, having significantly more 18:0 and less 16:1 and 18:1. Correspondingly, adipose tissue from the CSO group had significantly lower desaturase activity. The elevated 18:2 in adipose tissue from the CSO group confirmed that unsaturated fatty acids (including cyclopropenoid fatty acids) were protected from biohydrogenation. Further studies are needed to determine whether the repression of desaturase activity results from direct inhibition by cyclopropenoic acids or by higher dietary contents of 18:2.