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Effect of Soybean Lipid on Growth and Ruminal Nitrogen Metabolism in Cattle Fed Soybean Meal or Ground Whole Soybeans¹

University of Kentucky², Lexington 40546-0215

Abstract

Three experiments were conducted to determine the effect of soybean lipid on ruminal proteolysis of soybean meal (SBM) and ground whole soybeans (GSB). Experiment 1 was a 92-d growth experiment using 120 calves (206 kg) allotted to 12 pens of 10 calves each. Three replicate pens were assigned to each of the treatment supplements: low SBM (LSBM), low GSB (LGSB), high SBM (HSBM) and high GSB (HGSB). Calves received ad libitum amounts of corn silage top-dressed with the respective supplement (.81 kg/head). High protein supplements produced greater (P<.05) gains than low protein supplements, with HSBM calves gaining faster (P<.05) than HGSB calves and LSBM and LGSB calves having similar (P>.10) gains. In Exp. 2, 15 ruminally cannulated Angus x Hereford heifers (380 kg) fed corn silage were used to determine ammonia-N release from the treatment supplements: ground corn (control), GSB, SBM and SBM coated with soybean oil (SBMO). Heifers fed the control supplement had lower (P<.05) ruminal NH₃-N concentrations than those consuming soybean protein. Ruminal NH₃-N concentrations were similar (P>.10) for GSB and SBM; whereas, SBMO had lower (P<.10) concentrations than SBM through 3 h. In Exp. 3, two ruminally cannulated Angus x Jersey steers (250 kg) were used to determine in situ disappearance of SBM, GSB and SBMO. Total and feed N disappearances were greater (P<.001) for GSB than SBM or SBMO. Although SBM and SBMO were resistant to microbial attachment through 4 h, SBMO tended to have lower (P>.10) N disappearance than SBM when corrected for microbial N. Data from these experiments suggest that the endogenous lipid fraction of GSB did not protect soybean protein from ruminal proteolysis; however, physically coating SBM with oil apparently reduced proteolysis.

¹ This paper (no. 86-5-202) is published with the approval of the director of the Kentucky Agric. Exp. Sta.

² Dept. Anim. Sci.