Forty-two male lambs were allotted to three treatments at an average age of 25 days: left as intact rams, made cryptorchid, or castrated. The lambs remained with the ewes, without creep feed, on predominately bluegrass pasture, until an average age of 96 days. The male lambs and 14 ewe lambs of the same mean age were then allotted, within sex-type, to two subgroups: implanted subcutaneously at the base of the ear with 12 mg zeranol, and non-implanted. All lambs were confined to one lot and self-fed a ground concentrate-hay ration containing a calculated 10.6% total protein and 3,460 kilocalories of digestible energy/kilogram. Weaning weights and post-weaning ADG of rams and cryptorchids were significantly (P<.01) greater, and fat thickness less, than of wethers or ewes. Longissimus area/100 kg of carcass was significantly (P<.05) different only between rams and ewes. Zeranol resulted in ADG increases of 10.9, 9.8, 12.5 and 7.9% in rams, cryptorchids, wethers and ewes, respectively. Zeranol did not significantly affect any of the carcass characters measured. The sex-type × zeranol interaction was non-significant for all growth and carcass characters, indicating that these two variables were essentially additive.
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Wilson et al. (1972) studied this question.