Reiling B A, Berger L L, Faulkner D B, McKeith F K, Nash T G, Ireland F A
Department of Animal Sciences, University of Illinois, Urbana 61801, USA.
J Anim Sci. 1996 Sep;74(9):2043-51. doi: 10.2527/1996.7492043x.
Three studies were designed using a 2 x 2 factorial arrangement of treatments within each experiment to evaluate the effects of various management techniques on growth and carcass traits of once-calved heifers. In Exp. 1, 33 yearling (16 control [C] and 17 prenatally androgenized [PA]) and 39 once-calved (20 C and 19 PA) nonpregnant heifers were used to evaluate the effects of age and PA. Once-calved heifers were approximately 31 kg heavier (P < .03) on-test, initially consumed 11% more (P < .01) DM, and gained 11% faster (P < .08), but had similar (P = .44) gain to feed ratios (.138 vs. .131) as yearlings. Growth performance was not affected by PA. The yearling and once-calved heifers were then slaughtered at approximately 707 and 1,080 d of age, respectively. Despite maturity differences (P < .01), marbling scores (P = .26) and percentage of choice carcasses (P = .27) were similar. However, on the basis of newly accepted grading changes, percentage of once-calved heifer carcasses grading choice decreased from 57.3 to 34.4%. Organoleptic properties did not differ. Experiments 2 and 3 were then conducted to evaluate effects of commercially available products (melengestrol acetate [MGA] and Synovex-H) on feedlot characteristics of heifers following weaning of their first calf. In Exp. 2, 48 once-calved Simmental-based heifers were fed during the summer to a constant compositional fat thickness of .8 cm. Experiment 3 was conducted in the late fall and early winter, during which 52 moderately sized heifers were fed for 116 d postweaning and slaughtered. Performance of heifers in Exp. 2 was not affected by MGA. However, heifers fed MGA in Exp. 3 gained 9% faster (P < .05) than controls. In Exp. 2, Synovex-H tended to improve ADG (P < .09) and feed efficiency (P < .07), but did not affect performance in Exp. 3. Most carcass traits were not affected by either treatment. Nonpregnant, once-calved heifers seem to have a large capacity for efficient weight gain as compared with yearling heifers. However, hormonal compounds, such as testosterone propionate provided pre- or postnatally (Synovex-H), and MGA do not appear to provide the consistent, positive responses often seen with younger, more typical feedlot heifers.
在每个实验中，采用2×2析因处理设计了三项研究，以评估各种管理技术对初产小母牛生长和胴体性状的影响。在实验1中，使用33头一岁龄（16头对照[C]和17头产前雄激素化[PA]）和39头初产（20头C和19头PA）未怀孕的小母牛来评估年龄和PA的影响。初产小母牛在试验时体重约重31千克（P < 0.03），最初干物质摄入量多11%（P < 0.01），增重快11%（P < 0.08），但与一岁龄小母牛的料重比相似（P = 0.44）（分别为0.138和0.131）。生长性能不受PA的影响。然后，一岁龄和初产小母牛分别在约707日龄和1080日龄时屠宰。尽管成熟度存在差异（P < 0.01），大理石花纹评分（P = 0.26）和精选胴体百分比（P = 0.27）相似。然而，根据新采用的分级变化，初产小母牛胴体评为精选级的百分比从57.3%降至34.4%。感官特性没有差异。随后进行了实验2和实验3，以评估市售产品（醋酸美仑孕酮[MGA]和Synovex-H）对小母牛首次产犊断奶后育肥场特性的影响。在实验2中，48头以西门塔尔牛为基础的初产小母牛在夏季饲养至恒定的体脂厚度0.8厘米。实验3在秋末和初冬进行，在此期间，52头中等体型的小母牛断奶后饲养116天然后屠宰。实验2中小母牛的性能不受MGA的影响。然而，实验3中饲喂MGA的小母牛增重比对照组快9%（P < 0.05）。在实验2中，Synovex-H倾向于提高平均日增重（P < 0.09）和饲料效率（P < 0.07），但在实验3中对性能没有影响。两种处理对大多数胴体性状均无影响。与一岁龄小母牛相比，未怀孕的初产小母牛似乎具有很大的有效增重能力。然而，诸如产前或产后提供的丙酸睾酮（Synovex-H）和MGA等激素化合物，似乎并未产生年轻、更典型的育肥场小母牛常见的一致积极反应。
