Ten Holstein cows were used in a 15-wk nested factorial to evaluate the response to diets containing added fat from sunflower seeds high (greater than 65%) in linoleic acid (regular sunflower seeds) or high (80%) in oleic acid (high oleic acid variety sunflower seeds). Replicated periods were of 5 wk each, with data collected the last 3 wk of each period. Total mixed diets were 40% corn silage (DM basis), 15% alfalfa hay, and 45% concentrate mix. Concentrate mixes were control, 20% regular sunflower seeds, or 20% high oleic acid sunflower seeds in place of portions of the corn and soybean meal. Yields of milk (27.9, 25.4, and 28.8 kg/d) were similar for all diets, while 4% FCM (24.0, 19.2, and 24.0 kg/d) and SCM (24.8, 20.2, and 24.8 kg/d) were lower when cows were fed regular sunflower seeds. Percentages of fat (3.14, 2.43, and 2.92%) were reduced when cows were fed regular sunflower seeds, but protein (3.00, 3.24, and 3.03%) and total solids (12.12, 11.34, and 11.82%) were similar for all diets. Milk fat from cows fed regular sunflower seeds contained the highest proportions of unsaturated fatty acids with the lowest proportions from cows fed the control diet. Dry matter intakes (22.8, 20.6, and 21.9 kg/d) were similar. Molar percentages of ruminal acetate were lower and propionate higher when cows were fed regular sunflower seeds than when fed high oleic acid sunflower seeds or control. The fatty acid composition of dietary fat influenced the fatty acid composition of cows milk.

No abstract