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Supplemental Protein Withdrawal fron Corn-Corn Silage Rations: Effect of Weight and Corn Intake at Withdrawal

University of Wisconsin, Madison 53706

Abstract

Two finishing trials were conducted with 96 Holstein steers each to study the effect of body weight and corn intake at time of supplemental protein withdrawal. In both trials steers were fed a high grain (80% corn to 20% corn silage, dry matter) or a high silage (40% corn to 60% corn silage, dry matter) ration. In experiment 1, removal of supplemental protein when steers weighed 318, 386 or 454 kg had no effect (P>.05) on rate of gain, feed efficiency or carcass merit on either ration when compared to steers fed protein continuously. Steers fed the high grain ration gained 8% faster and produced heavier carcasses with lower percent retail cuts than those fed the high silage ration (P<05).

Withdrawal of supplemental protein in experiment 2 when daily corn intake (above that in silage) reached 4.5, 5.9 or 7.3 kg had no effect (P>.05) on rate of gain, feed efficiency of carcass merit for steers fed the high grain ration. Similar results were observed when supplemental protein was removed at 4.5 kg corn intake on the high silage ration. Feed consumption did not reach the higher levels of grain intake due to the high dry matter content of the silage. However, protein withdrawal at 84 days (425 kg body weight) or 140 days (483 kg body weight) resulted in comparable gains, feed efficiency and carcass characteristics to steers fed protein continuously for the 206 day trial. In experiment 2, steers fed the high grain ration gained faster and produced heavier carcasses which graded higher than steers fed highsilage rations (P<.05).

Daily crude protein intakes remained at .87 kg (8.7% dry matter intake) or higher in both finishing trials following supplemental protein removal.

Rumen ammonia (NH₃-N) was measured for 10 heifers fed equal amounts of a corn-corn silage mix (70:30, dry matter) with a protein supplement or a withdrawal supplement. Rumen NH₃-N levels were higher at 0, 1,4 and 6 hr after feeding for heifers fed protein (P<.05). Ammonia-N levels were low (<5 mg/100 ml) at 0 and 6 hr for the withdrawal animals and suggest a possible ruminal NH₃-N insufficiency for maximal microbial growth.

¹ Department of Meat and Animal Science. Research was supported by the College of Agricultural and Life Sciences. This is Paper No. 702 from the Department of Meat and Animal Science.

² The author is grateful to the Oscar Mayer Company for their support and cooperation in this study.