Mallory D A, Wilson D J, Busch D C, Ellersieck M R, Smith M F, Patterson D J
Division of Animal Science, S132 ASRC, University of Missouri, Columbia, 65211, USA.
J Anim Sci. 2010 Nov;88(11):3568-78. doi: 10.2527/jas.2010-3084. Epub 2010 Jul 23.
Two experiments evaluated long-term progestin-based estrus-synchronization programs on the basis of potential for use in facilitating fixed-time AI in estrous cycling and prepubertal beef heifers. In Exp. 1, heifers were assigned to 1 of 2 treatments by age, BW, and estrous cyclicity status. Heifers assigned to the melengestrol acetate-PGF(2α) protocol (MGA-PG; n = 50) received MGA (0.5 mg·animal(-1)·d(-1)) in a 1.0-kg carrier from d 0 to 13 and were administered PGF(2α) (25 mg, intramuscularly) 19 d after MGA withdrawal (d 32). Heifers assigned to the Show-Me-Synch protocol (n = 49) received a controlled internal drug release (CIDR) insert (1.38 g of progesterone) from d 2 to 16 followed by PGF(2α) administration 16 d after CIDR removal (d 32). All heifers were fitted with HeatWatch estrus-detection transmitters at the time of progestin removal for continuous estrus detection through the synchronized period after PGF(2α). In Exp. 2, heifers (n = 396) were assigned to the same 2 treatments described in Exp. 1 by age, BW, and reproductive tract score. Heifers in Exp. 2, however, were fitted with HeatWatch estrus-detection transmitters at PGF(2α) to characterize estrus-distribution patterns during the synchronized period after PGF(2α). Heifers in both experiments were inseminated approximately 12 h after the onset of estrus. In Exp. 1, estrous response after PGF(2α) and mean interval to estrus after PGF(2α) did not differ between MGA-PG and Show-Me-Synch treatments (P = 0.97). The variance for interval to estrus after PGF(2α) tended (P = 0.06) to be reduced among MGA-PG-treated heifers compared with Show-Me-Synch-treated heifers. Conception to AI, AI pregnancy, and final pregnancy rates did not differ (P > 0.1) between treatments. In Exp. 2, estrous response after PGF(2α) was greater (P = 0.01) among Show-Me-Synch-treated heifers (92%) compared with MGA-PG-treated heifers (85%); however, mean interval to estrus after PGF(2α) did not differ (P = 0.74) between MGA-PG (57.4 ± 2.5 h) and Show-Me-Synch (56.2 ± 2.5 h) treatments. The variance for interval to estrus after PGF(2α) was reduced (P < 0.01) among Show-Me-Synch-treated vs. MGA-PG-treated heifers. Conception to AI, AI pregnancy, and final pregnancy rates did not differ (P > 0.1) between treatments. In summary, the Show-Me-Synch protocol compared favorably with the MGA-PG protocol on the basis of estrous response, synchrony of estrus, and resulting fertility after treatment administration.
两项试验基于在发情周期和青春期前的小母牛中促进定时人工授精的潜在用途，对基于孕激素的长期发情同步化程序进行了评估。在试验1中，根据年龄、体重和发情周期状态，将小母牛分配到两种处理中的一种。分配到醋酸美仑孕酮 - PGF₂α方案（MGA - PG；n = 50）的小母牛，从第0天至第13天在1.0千克载体中接受MGA（0.5毫克·动物⁻¹·天⁻¹），并在停用MGA后19天（第32天）肌肉注射PGF₂α（25毫克）。分配到Show - Me - Synch方案（n = 49）的小母牛，从第2天至第16天接受一个控制内部药物释放（CIDR）装置（1.38克孕酮），然后在取出CIDR后16天（第32天）给予PGF₂α。在去除孕激素时，所有小母牛都佩戴了HeatWatch发情检测发射器，以便在PGF₂α后的同步期持续检测发情。在试验2中，根据年龄、体重和生殖道评分，将396头小母牛分配到试验1中描述的相同两种处理。然而，试验2中的小母牛在PGF₂α时佩戴HeatWatch发情检测发射器，以表征PGF₂α后同步期的发情分布模式。两个试验中的小母牛在发情开始后约12小时进行人工授精。在试验1中，PGF₂α后的发情反应以及PGF₂α后到发情的平均间隔时间在MGA - PG和Show - Me - Synch处理之间没有差异（P = 0.97）。与Show - Me - Synch处理的小母牛相比，MGA - PG处理的小母牛在PGF₂α后到发情的间隔时间的方差有降低的趋势（P = 0.06）。处理之间的人工授精受胎率、人工授精妊娠率和最终妊娠率没有差异（P > 0.1）。在试验2中，Show - Me - Synch处理的小母牛（92%）在PGF₂α后的发情反应比MGA - PG处理的小母牛（85%）更强烈（P = 0.01）；然而，MGA - PG（57.4 ± 2.5小时）和Show - Me - Synch（56.2 ± 2.5小时）处理之间PGF₂α后到发情的平均间隔时间没有差异（P = 0.74）。与MGA - PG处理的小母牛相比，Show - Me - Synch处理的小母牛在PGF₂α后到发情的间隔时间的方差降低了（P < 0.01）。处理之间的人工授精受胎率、人工授精妊娠率和最终妊娠率没有差异（P > 0.1）。总之，基于发情反应、发情同步性以及给药后产生的繁殖力，Show - Me - Synch方案与MGA - PG方案相比具有优势。
