Effect of soybean hulls, soy lecithin, and soapstock mixtures on ruminal fermentation and milk composition in dairy cows

Two experiments were conducted to determine effects of soybean hulls, soy lecithin, and soapstock mixtures on ruminal fermentation, milk composition, and ruminal microbial populations. In Experiment 1, 20 Holstein dairy cows were assigned to one of five total mixed rations (TMR) in replicated 5 x 5 Latin squares to measure the effect of TMR on intake and milk composition. Four ruminally fistulated cows were used in a 4 x 5 Youden square to measure the effect of TMR on ruminal fermentation. The TMR consisted of 40 or 50% alfalfa and corn silages, 13% soybean hulls, and 47 or 37% of a concentrate containing either 2.25% soybean oil; 2.25% lipid from a mixture of soybean hulls, soy lecithin, and soapstock; or no added lipid. The ratios of soy lecithin to soapstock evaluated were 1:1, 2.5:1, and 4:1 (dry basis). The TMR containing soy lecithin and soapstock at ratios of 1:1 and 2.5:1 resulted in higher milk C-18:2 than did the soybean oil TMR. Rate of ruminal NDF digestion of soybean hulls was reduced for the soybean oil TMR. In Experiment 2, a semi-continuous culture system was used to determine effects of soybean oil or an optimal mixture of soy lecithin and soapstock (1:1, wt/wt) on fermentation of soybean hulls and microbial populations. The TMR containing the lipid mixture increased the ratio of acetate to propionate compared with the TMR containing soybean oil and resulted in higher total protozoal counts than did the control TMR. The TMR containing mixtures of soy lecithin and soapstock at ratios of 1:1 and 2.5:1 elevated milk C-18:2, and no negative effect on NDF digestion was detected, indicating some degree of ruminal protection.