Fatty acid composition and fatty acid elongase and stearoyl-CoA desaturase activities in tissues of steers fed high oleate sunflower seed.

The effects of a high oleate sunflower seed diet on tissue composition and on fatty acid elongation and desaturation enzyme activities were investigated. Three Simmental calves were fed a standard corn-based diet (2.6% fat); three others were fed the corn-based diet containing 20% high oleate sunflower seed (10.4% fat). Blood samples and perianal adipose tissue samples were obtained at 7, 90 and 180 d on trial. Samples of liver, longissimus dorsi muscle and intestinal mucosa were obtained at the termination of the experiment (195 d on trial). Plasma oleate was higher (P < 0.05) in the cattle fed the sunflower seed, and oleate, myristate (P < 0.05) and stearate (P < 0.06) were elevated in perianal adipose tissue in response to the greater lipid content of the dietary sunflower seed. Dietary sunflower seed decreased the concentration of stearate (P < 0.05) in liver. The high oleate diet significantly (P < 0.05) increased the activity of stearoyl-CoA desaturase activity in muscle, and numerical increases in desaturase activity were observed in liver, adipose and small intestine samples. Elongase activity was unaffected by diet. Because stearate is the primary fatty acid available for absorption in ruminants, elevated oleate in plasma and depressed stearate in liver of cattle fed sunflower seed may have reflected an adaptive response of stearoyl-CoA desaturase in their tissues.