AVOPARCIN, MONENSIN AND ZERANOL FOR STEERS FINISHING ON BARLEY DIETS

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Abstract
Ninety Hereford steers, weighting 362 ± 30 kg, were allocated to three replications of six treatments as follows: basal diet which consisted of 5.9 ± 0.73 kg·head−1∙day−1 steam-rolled barley at the start of the trial (78% of total diet) increasing to 10.1 ± 0.52 kg·head−1∙day−1 by the end of the trial (85% of total diet), 0.72 kg·head−1∙day−1 grass hay and 1 kg of mineral/vitamin supplement; basal diet to which 400 mg·head−1∙day−1 avoparcin was added via the mineral supplement; basal ration with added monensin given via the mineral supplement at 280 mg·head−1∙day−1; basal diet with an ear implant of zeranol; basal diet, avoparcin and zeranol; basal diet, monensin and zeranol. Average daily liveweight gains (ADG), feed intakes and carcass characteristics were measured and feed:gain ratios were calculated. Avoparcin, monensin and zeranol, when given alone, did not significantly influence any measured production trait. However, avoparcin and zeranol, when given together, increased ADG by 20.3% and reduced feed:gain ratio by 15.3% (P < 0.05). Similarly, monensin and zeranol in combination increased ADG by 24.6% and reduced feed:gain ratio by 20.7% (P < 0.05). Carcass characteristics were not influenced by any of the treatments. Key words: Avoparcin, monensin, zeranol, barley, beef steers