Effect of Monensin on Feed Efficiency of Feedlot Cattle

Abstract

A preliminary experiment investigated the effect of 0, 100, 500 and 750 mg monensin, orally administered daily, upon live weight gain and efficiency of feed utilization by fattening cattle. Monensin dosages of 500 mg and below improved performance of fattening cattle. Two additional experiments were conducted to define the dose response relationships between 0, 2.7, 5.5, 11, 22, 33, 44 and 88 ppm monensin and daily gain, feed consumption and feed efficiency. All monensin dosages except 88 ppm produced daily gains that were equal to or greater than the nontreated controls. The largest improvement in daily gain was 5.2% at 11 ppm monensin. Feed consumption decreased, progressively, with increasing monensin dosage. Feed consumption was reduced 3.5% at 11 ppm and 13.1% at 33 parts per million. All monensin treatments improved feed efficiency. At 11 and 33 ppm feed efficiency was improved 10 and 17%, respectively. Analysis of rumen content samples indicated that monensin decreased the molar proportions of acetate, butyrate and valerate and increased the molar proportion of propionate and isovalerate. Blood glucose, urea nitrogen and insulin all tended to increase with the feeding of monensin at levels below 44 parts per million.