Effect of Monensin on Performance and Plasma Metabolites in Growing-Finishing Steers

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Abstract
The effects of level of monensin on performance, feed utilization, carcass characteristics, plasma free amino acids and urea-nitrogen were studied with 96 yearling steers in a growing-finishing trial. Diets were composed of corn silage, ground shelled corn and soybean meal with monensin added to give the following treatments: (A) control, (B) 100 mg, (C) 200 mg and (D) increasing levels of 150 mg, 200 mg, 250 mg and then 300 mg monensin/head/ day. Feed intake on a dry-matter basis for the four treatment groups (A through D, respectively) were: 8.21; 8.07; 7.85 and 7.79 kg per day. Feed intake on all monensin treatments was lower (P<.01) than the control intake. Feed efficiencies (DM/gain) were improved (P<.01) with monensin as follows-. 7.97, 7.21, 6.83 and 6.95 for control, 100 mg, 200 mg and increasing levels, respectively. Average daily gains were 1.03, 1.12, 1.15 and 1.12 kg for the same treatment groups, respectively, and were higher (P<.10) for all monensin treatments. Carcasses from monensin-fed steers were heavier, tended to be fatter, and had more marbling and higher yield grades than those of control steers (P<.05). Differences observed in quality grade and ribeye area were not significant. Differences observed in plasma urea nitrogen (PUN), plasma glucose (GLU) or plasma amino acids (PAA) were not significant (P>.10). Differences observed for all metabolites with time on feed were significant (P<01). PUN increased with time on feed while GLU decreased. PAA increased during the early periods, then decreased with time on feed. Copyright © 1978. American Society of Animal Science . Copyright 1978 by American Society of Animal Science.