Monensin Levels for Growing and Finishing Steers

Abstract

Two trials were conducted to study the influence of level of monensin on: (1) growth rate and ruminal volatile fatty acids of steers during a 140-day grazing period, and (2) growth, efficiency, volatile fatty acids and carcass characteristics of steers in a 157-day finishing study. In the first trial, 72 Angus steers were randomly assigned to four groups and fed either 0, 25, 50 or 100 mg monensin per head daily in .91 kg ground shelled corn as carrier while grazing Kentucky bluegrass-clover pasture. Average daily gains were .55, .55, .73 and .68 kg for the four groups, respectively, and were greater (P<.01) for steers fed 50 or 100 mg monensin than for the control or the 25 mg groups of steers. Ruminal propionate increased (P<.05) as level of monensin fed increased. In the second trial, 96 steers were allotted to four treatments and fed 0, 100, 200 or 300 mg monensin per steer daily in 4.54 kg of a grain mixture, plus corn silage ad libitum. Each treatment consisted of three pens containing eight steers per pen. Average daily gains for the four treatment groups were: 1.14, 1.26, 1.23 and 1.18 kg/day, respectively. Feed intake tended to decrease as level of monensin fed increased. Feed efficiency (dry matter) was improved (P<.01) in all groups fed monensin. Molar percentages of acetate and butyrate decreased and propionate increased as the level of monensin fed increased. Carcass characteristics were not influenced (P<.05) by level of monensin fed, but steers fed 300 mg per day tended to have lower marbling scores, smaller ribeye area and less fat over the rib. Copyright © 1977. American Society of Animal Science . Copyright 1977 by American Society of Animal Science.