Arnold A M, Meyer H H
Dept. of Anim. Sci., Oregon State University, Corvallis 97331.
J Anim Sci. 1988 Oct;66(10):2468-75. doi: 10.2527/jas1988.66102468x.
Two concurrent trials were conducted to examine the effects of gender, time of castration, genotype and feeding regimen on lamb growth rate and carcass fatness. Trial 1 compared Polypay and Coopworth x Polypay male lambs either left intact or castrated early, mid or late in growth. Trial 2 compared Hampshire-sired lambs (females, early castrate wethers and late castrate wethers) from Suffolk x Coopworth dams and whiteface x Coopworth dams. Gender and time of castration significantly affected growth rate in Trial 1 but not in Trial 2. Rams were more efficient than wethers, but no other gender or time of castration effects on feed efficiency were observed. Delaying castration and pasture grazing both reduced fatness. Lambs grazed on irrigated pastures until they weighed 41 kg then finished in drylot had a lower dressing percentage than lambs fed in the drylot throughout, but USDA quality grades were similar. Substitution of Polypay genes by Coopworth genes in crossbred lambs did not significantly alter any of the fatness traits measured but increased ribeye area. Hampshire-sired lambs grew faster than whiteface lambs, particularly in drylot. They had a higher dressing percentage without increased fatness, apparently because of greater muscling in ribeye and leg.
进行了两项同期试验，以研究性别、去势时间、基因型和饲养方式对羔羊生长速度和胴体脂肪含量的影响。试验1比较了完整的以及在生长早期、中期或晚期去势的波利佩公羊和库泊华斯×波利佩杂交公羊。试验2比较了来自萨福克×库泊华斯母羊和白面×库泊华斯母羊的汉普夏种公羊所生的羔羊（母羊、早期去势阉羊和晚期去势阉羊）。性别和去势时间在试验1中对生长速度有显著影响，但在试验2中没有。公羊比阉羊生长效率更高，但未观察到其他性别或去势时间对饲料效率的影响。延迟去势和放牧都会降低脂肪含量。在灌溉牧场上放牧至体重达41千克然后在干圈舍育肥的羔羊，其屠宰率低于全程在干圈舍饲养的羔羊，但美国农业部质量等级相似。在杂交羔羊中用库泊华斯基因替代波利佩基因，并未显著改变所测的任何脂肪性状，但增加了眼肌面积。汉普夏种公羊所生的羔羊比白面羔羊生长更快，尤其是在干圈舍饲养时。它们的屠宰率更高且脂肪含量未增加，显然是因为眼肌和腿部肌肉更发达。
