Effect of Monensin on the Performance of Forage - Fed Lambs

Abstract

Seventy-five wether lambs were randomly assigned to three replications of five treatment diets. Diets consisted of pelleted subclover (Trifolium subterraneum) – perennial grass hay containing 5% molasses and 0, 5.5, 11, 22 or 33 mg monensin/kg. Initial average live weights were 37.3, 36.7, 38.2, 37.8 and 39.3 kg for lambs fed the 0, 5.5, 11, 22 and 33 mg monensin/kg diets, respectively. During the 56-day feeding period, there were no beneficial effects on animal performance associated with the inclusion of monensin at any level. Feed intake (P<.01) and average daily gain (P<.10) declined linearly as level of monensin in the diet increased. Although feed efficiency was not affected by level of monensin during the 56-day period as a whole, it declined linearly (P<.10) with increasing monensin level during the first 28 days of the trial. Few consistent differences in lamb carcass characteristics could be attributed to the diets. Those that were observed (in cold carcass weight and fat thickness) were probably due to differences in the live weights of lambs slaughtered rather than to monensin, per se. Low palatability of the diets containing monensin is believed to be an important contributor to the poor performance of the lambs fed monensin in this trial.