Journal of Animal Science, Vol 71, Issue 7 1677-1687, Copyright © 1993 by American Society of Animal Science

JOURNAL ARTICLE

Ruminal escape protein for lightweight feedlot calves

R. A. Zinn and F. N. Owens
Department of Animal Science, Imperial Valley Agricultural Center, University of California, El Centro 92243.

Effects of supplemental ruminal escape protein (REP) were evaluated in an 84-d growth study involving 140 feedlot steers (198 kg) and in a site of digestion study involving four steers (149 kg). Dietary treatments were as follows: 1) basal diet; 2) basal diet plus 2% of a REP blend (1/3 blood meal, 1/3 meat and bone meal, and 1/3 feather meal); 3) basal diet plus 4% REP; and 4) basal diet plus 6% REP. The basal diet contained 18% alfalfa hay, 10% sudangrass hay, 61% steam-flaked corn, 2.5% yellow grease, 6% molasses, and 2.5% supplement. The basal diet contained 12.2% CP, and urea was the sole source of supplemental N. There was a quadratic effect (P < .05) of REP supplementation on rate and efficiency of gain. The greatest response was with 2% REP, which increased rate and efficiency of gain by 13.4 and 8.4%, respectively, over that of the basal diet. Protein supplementation had a quadratic effect (P < .05) on the NE value of the diet. The addition of 2% supplemental REP increased the NE of the diet by 6.6%. In the site of digestion trial, supplemental REP linearly increased (P < .01) passage of nonammonia and amino acid N to the small intestine. Compared with estimated amino acid requirements and with muscle composition, postruminal supplies of arginine, histidine, lysine, methionine, and phenylalanine were the limiting amino acids in the basal diet. Excess bypass protein, by placing an additional demand on arginine for detoxification of ammonia, may limit growth and performance.

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