Effect of Dietary Monensin on Coccidial Oocyst Numbers, Feedlot Performance and Carcass Characteristics of Lambs

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Abstract
Five levels of monensin (0, 5.5, 11, 22 and 33 mg/kg) and two energy levels (2.61 and 3.18 Meal DE/kg) were fed in a factorial treatment arrangement with 249 feeder lambs. Initially, 95.6% of the lambs sampled were shedding coccidial oocysts. All levels of monensin decreased fecal oocyst numbers. Over a 70-day feeding period, feed intake was lowered .049 kg/day for each 10 mg/kg increase in monensin in the diet (P<.01). The relationship between monensin level in milligrams per kilogram (X) and live weight gains (adjusted to a constant dressing percentage) in kilograms per day (Y) was Y = .265 + .0019X − .00008X2 (P<.05). For feed efficiency (feed/adj. gain), there was an interaction between monensin and energy level in the diet (P<.01). With the 3.18 Meal DE diets, the only improvement was at 5.5 mg/kg of monensin. In contrast, efficiency was improved at all monensin levels with the 2.61 Meal DE diets; with a maximum improvement of 23.2% at a calculated monensin level of 19.6 mg/kg. Monensin decreased ruminal acetate (P<.05) and butyrate (P<.01) and increased propionate (P<.01). However, the response was greater with the 2.61 Meal DE diets. Copyright © 1979. American Society of Animal Science . Copyright 1979 by American Society of Animal Science.