Tatum J D, Klein B J, Williams F L, Bowling R A
Colorado State University, Fort Collins 80523.
J Anim Sci. 1988 Aug;66(8):1942-54. doi: 10.2527/jas1988.6681942x.
One hundred seventy-three steer calves, selected at weaning to represent USDA classifications for frame size (Large, L; Medium, M; Small, S) and muscle thickness (No. 1, No. 2, No. 3), were assigned to three finishing diets (grain, 3.03 Mcal ME/kg DM; silage, 2.46 Mcal ME/kg DM; forage, 2.06 Mcal ME/kg DM), forming a 3 x 3 x 3 factorial with unequal subclass numbers. The steers were slaughtered at constant weights corresponding to their respective frame size classifications (L = 590 kg, M = 499 kg; S = 408 kg). Individual live weights were recorded every 28 d during finishing and, following slaughter, one side of each carcass was dissected into muscle, bone and fat. Diet interacted with frame size to affect growth rate. Frame-related differences in growth rate were very pronounced among grain-fed steers (L greater than M greater than S) but became smaller in magnitude as feeding intensity was reduced. Diet also had a significant effect on percentage separable carcass fat, despite the fact that the steers were slaughtered at a similar percentage (approximately 60%) of their estimated potential mature weights. Carcasses produced by grain-finished steers were fattest, and those produced by forage-finished cattle were leanest. The comparative fatness of steers finished on silage was dependent on frame size. Within the L class, carcasses produced by silage-finished steers were comparatively lean and were similar in fatness to carcasses produced by forage-finished cattle. Conversely, S steers finished on silage produced carcasses that were comparable in fatness to carcasses from grain-finished cattle. Frame-related differences in percentage carcass fat were significant only within the silage treatment group (S greater than L). Differences in carcass muscle-to-bone ratio were directionally consistent with visually discernible differences in feeder cattle muscling (No. 1 greater than No. 2 greater than No. 3). The effects of muscle thickness on muscle-to-bone ratio were most pronounced within the L class.(ABSTRACT TRUNCATED AT 400 WORDS)
173头断奶期的阉牛犊，根据美国农业部的体格大小分类（大，L；中，M；小，S）和肌肉厚度分类（1号、2号、3号）进行挑选，被分配到三种育肥日粮（谷物，3.03兆卡代谢能/千克干物质；青贮料，2.46兆卡代谢能/千克干物质；草料，2.06兆卡代谢能/千克干物质），形成一个3×3×3的析因设计，各亚组数量不等。这些阉牛在与各自体格大小分类相对应的恒定体重下屠宰（L = 590千克，M = 499千克；S = 408千克）。育肥期间每28天记录个体活重，屠宰后，将每具胴体的一侧分解为肌肉、骨骼和脂肪。日粮与体格大小相互作用影响生长速度。在谷物育肥的阉牛中，与体格相关的生长速度差异非常明显（L＞M＞S），但随着饲养强度降低，差异幅度变小。日粮对可分离胴体脂肪百分比也有显著影响，尽管这些阉牛屠宰时的体重占其估计潜在成熟体重的百分比相似（约60%）。谷物育肥的阉牛生产的胴体最肥，草料育肥的牛生产的胴体最瘦。青贮料育肥的阉牛的相对肥瘦程度取决于体格大小。在L组中，青贮料育肥的阉牛生产的胴体相对较瘦，其肥瘦程度与草料育肥的牛生产的胴体相似。相反，青贮料育肥的S阉牛生产的胴体肥瘦程度与谷物育肥的牛生产的胴体相当。胴体脂肪百分比与体格相关的差异仅在青贮料处理组内显著（S＞L）。胴体肌肉与骨骼比例的差异在方向上与育肥牛肌肉的视觉差异一致（1号＞2号＞3号）。肌肉厚度对肌肉与骨骼比例的影响在L组中最为明显。（摘要截选至400字）
