Butylsoyamide increases unsaturation of fatty acids in plasma and milk of lactating dairy cows

This study was designed to determine whether dietary butylsoyamide increased unsaturation of fatty acids in milk of lactating dairy cows. Nine Holstein cows were fed three diets in a 3 x 3 Latin square design, replicated three times. One diet was a control with no added fat, and the other two diets were supplemented (3.5% of the DM) with either soybean oil or butylsoyamide. Milk yields and DMI were similar for the three diets. Milk fat percentage and FCM were reduced by soybean oil, but not by butylsoyamide. Milk protein yield was reduced when butylseyamide was fed, and milk fat yield was reduced when soybean oil was fed. The soybean oil supplement disrupted ruminal fermentation, causing total VFA and acetate concentrations to decline; the butylsoyamide supplement had no effect on ruminal VFA. The proportion of linoleic acid in plasma fatty acids was similar with the control (54.3%) and soybean oil (52.0%) diets but was higher with butylsoyamide (59.0%). Linoleic acid concentration in milk fat averaged 3.60, 4.77, and 6.28% for the control, soybean oil, and butylsoyamide diets, respectively. Conversion of soybean oil to butylsoyamide protected unsaturated fatty acids from ruminal biohydrogenation, causing linoleic acid to increase in the plasma and milk of dairy cows.