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 com position, and ruminal microbial populations. In Experiment 1, 20 Holst ein 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 inta ke and milk composition. Four ruminally fistulated cows were used in a 4 x 5 Youden square to measure the effect of TMR on ruminal fermentat ion. The TMR consisted of 40 or 50% alfalfa and corn silages, 13% soyb ean hulls, and 47 or 37% of a concentrate containing either 2.25% soyb ean oil; 2.25% lipid from a mixture of soybean hulls, soy lecithin, an d soapstock; or no added lipid. The ratios of soy lecithin to soapstoc k evaluated were 1:1, 2.5:1, and 4:1 (dry basis). The TMR containing s oy lecithin and soapstock at ratios of 1:1 and 2.5:1 resulted in highe r milk C-18:2 than did the soybean oil TMR. Rate of ruminal NDF digest ion of soybean hulls was reduced for the soybean oil TMR. In Experimen t 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. Th e TMR containing the lipid mixture increased the ratio of acetate to p ropionate compared with the TMR containing soybean oil and resulted in higher total protozoal counts than did the control TMR. The TMR conta ining 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 de tected, indicating some degree of ruminal protection.