Healy V M, Boyd G W, Gutierrez P H, Mortimer R G, Piotrowski J R
Department of Animal Science, Colorado State University, Fort Collins 80523.
J Anim Sci. 1993 Feb;71(2):291-7. doi: 10.2527/1993.712291x.
The objectives of this study were to determine 1) the effect of bull:heifer ratio on reproductive performance and associated costs and return on heifers in synchronized estrus and 2) the effect of estrus synchronization on reproductive performance and economic variables, in a multiple-sire, pasture breeding situation. Eight hundred yearling beef heifers and 28 mature, sexually experienced beef bulls were allotted to four treatments (two replicates per treatment) at bull:heifer ratios of 2 per 100 (1:50; Treatment 1), 2 per 100 (1:50; Treatment 2), 4 per 100 (1:25; Treatment 3), and 6 per 100 (1:16; Treatment 4). Treatment 1 (control) used nonsynchronized heifers, whereas heifers in Treatments 2, 3, and 4 were synchronized using the 33-d melengestrol acetate (MGA)-prostaglandin F2 alpha (PGF2 alpha) program. Pregnancy results after a 28-d breeding season indicate that there may be a limit to how many estrus-synchronized heifers bulls can impregnate. Treatment 2 showed a 6% decrease (P < .10) in pregnancy rate (77%) compared with Treatment 3 (83%), indicating that the bulls probably were not able to service all the synchronized heifers. Treatments 3 and 4 had similar pregnancy rates (83 and 84%, respectively). Treatment 4 had a 3-d advantage (P < .01) over Treatment 3 in average day of conception. However, based on economic analysis, Treatment 3 exhibited greater returns. Estrus synchronization failed to provide any advantage in pregnancy rate or day of conception. For unknown reasons, the control, nonsynchronized heifers cycled and conceived as if they were synchronized.(ABSTRACT TRUNCATED AT 250 WORDS)
1）在同期发情情况下，公牛与小母牛比例对繁殖性能、相关成本及小母牛回报的影响；2）在多头公牛、牧场配种的情况下，发情同期化对繁殖性能和经济变量的影响。800头一岁龄肉用小母牛和28头成熟、有性经验的肉用公牛被分配到四种处理方式（每种处理两个重复），公牛与小母牛的比例分别为每100头2头（1:50；处理1）、每100头2头（1:50；处理2）、每100头4头（1:25；处理3）和每100头6头（1:16；处理4）。处理1（对照）使用未同期发情的小母牛，而处理2、3和4中的小母牛使用33天醋酸甲地孕酮（MGA）-前列腺素F2α（PGF2α）方案进行同期发情处理。28天繁殖期后的妊娠结果表明，公牛能够使同期发情的小母牛受孕的数量可能存在限制。与处理3（83%）相比，处理2的妊娠率（77%）下降了6%（P < 0.10），这表明公牛可能无法使所有同期发情的小母牛受孕。处理3和4的妊娠率相似（分别为83%和84%）。处理4在平均受孕日比处理3有3天的优势（P < 0.01）。然而，基于经济分析，处理3表现出更高的回报。发情同期化在妊娠率或受孕日方面未显示出任何优势。出于未知原因，对照、未同期发情的小母牛像经过同期发情处理一样发情并受孕。（摘要截短至250字）
