Performance and profiles of milk fatty acids of cows fed full fat, heat-treated soybeans using various processing methods

Twenty-four multiparous Holstein cows (48 d in lactation) were used in an 8-wk trial employing a completely randomized block design to determine the effect of heat treatment of full fat soybeans on the fatty acid composition of milk fat. Treatments consisted of a total mixed ration supplemented with 1) ground raw, 2) extruded, 3) micronized, or 4) roasted soybeans included at 17.5% of the dry matter of the total mixed ration. Dietary treatment had no effect on body weight, yields of milk or solids-corrected milk, fat percentage, or yield of milk fat or protein. Cows fed ground raw soybeans had a higher dry matter intake and a higher percentage of protein in milk than those fed heat-treated soybeans. The concentrations of saturated fatty acids from C-8:0 to C-16:0 were lower, and cis-Delta-9-C-18:1 tended to be higher, in the milk fat of cows fed heat-treated soybeans than in the milk fat of cows fed ground raw soybeans. The concentration of trans-Delta-11-C-18:1 was lowest for cows fed ground raw soybeans, intermediate for cows fed micronized and roasted soybeans, and highest for cows fed extruded soybeans. Cows fed extruded soybeans had lower concentrations of C-18:2 and C-18:3 than did cows fed micronized or roasted soybeans; cows fed ground raw soybeans had intermediate concentrations of C-18:2 and C-18:3.