Coleman S W, Evans B C, Guenther J J
Grazinglands Research Laboratory, ARS, USDA, El Reno, OK 73036.
J Anim Sci. 1993 Jan;71(1):86-95. doi: 10.2527/1993.71186x.
The objectives of this study were to examine the effects of a low vs moderate rate of gain during the growing phase on empty body and carcass composition during finishing of Angus and Charolais steers of two ages. Forty-eight Angus and 48 Charolais steers that were either spring-born (OLDER) or fall-born (YOUNGER) were fed two diets (alfalfa pellets [CON] or cubed grass-alfalfa hay, wheat straw, cottonseed hulls, and soybean meal [RES]) for a growing period followed by a conventional feedlot period. The feedlot period started when the YOUNGER-CON steers weighed the same as the OLDER-RES steers. At that time, an interaction of age x diet occurred in empty body fat content (P < .10), whereas breed and age x diet affected carcass fat content (P < .01). OLDER-CON steers were larger (average 378 kg empty BW) and fatter than the other, smaller groups (average 222 kg). Angus carcasses were fatter than Charolais carcasses (P < .01). At the end of the finishing phase, compensating steers (OLDER-RES) had fatter carcasses than OLDER-CON steers. Empty body fat content was affected by a breed x age x diet interaction (P < .10). Allometric regressions (Y = aXb) of fat on empty BW indicated that empty body fat accretion was greater in Angus than in Charolais and in YOUNGER than in OLDER steers. A breed x age x diet interaction (P < .10) indicated that OLDER-Angus had higher fat accretive rates than YOUNGER-Angus, whereas OLDER-CON-Charolais steers deposited fat more slowly than the remaining groups. These data suggest that steers receiving feedlot diets at light weights, whether young in age or previously restricted, accumulate fat more rapidly than do larger steers. This feeding strategy may be an advantage in late-maturing types, but moderate growth through approximately 75% of slaughter weight is recommended for early-maturing types.
本研究的目的是考察两个年龄段的安格斯和夏洛来阉牛在生长阶段低生长速率与中等生长速率对育肥期胴体组成和空腹体重的影响。48头春季出生（年龄较大）或秋季出生（年龄较小）的安格斯阉牛和48头夏洛来阉牛，在生长阶段饲喂两种日粮（苜蓿颗粒料[对照日粮]或切碎的禾本科-苜蓿干草、小麦秸秆、棉籽壳和豆粕[试验日粮]），随后进入传统的育肥期。育肥期开始于年龄较小的对照日粮组阉牛体重与年龄较大的试验日粮组阉牛体重相当时。此时，空腹体脂含量出现年龄×日粮的交互作用（P<0.10），而品种以及年龄×日粮影响胴体脂肪含量（P<0.01）。年龄较大的对照日粮组阉牛体型更大（空腹体重平均378千克），比其他体型较小的组（平均222千克）更肥。安格斯牛的胴体比夏洛来牛的胴体更肥（P<0.01）。在育肥阶段结束时，补偿生长的阉牛（年龄较大的试验日粮组）胴体比年龄较大的对照日粮组阉牛更肥。空腹体脂含量受品种×年龄×日粮的交互作用影响（P<0.10）。脂肪相对于空腹体重的异速生长回归方程（Y = aXb）表明，安格斯阉牛的空腹体脂肪沉积量高于夏洛来阉牛，年龄较小的阉牛高于年龄较大的阉牛。品种×年龄×日粮的交互作用（P<0.10）表明，年龄较大的安格斯阉牛脂肪沉积速率高于年龄较小的安格斯阉牛，而年龄较大饲喂对照日粮的夏洛来阉牛脂肪沉积比其他组更慢。这些数据表明，体重较轻时接受育肥牛日粮的阉牛，无论年龄小还是之前生长受限，比体型较大的阉牛积累脂肪更快。这种饲养策略对于晚熟类型可能是一个优势，但对于早熟类型，建议在达到屠宰体重约75%之前适度生长。
