Stegner J E, Kojima F N, Bader J F, Lucy M C, Ellersieck M R, Smith M F, Patterson D J
Department of Animal Science, University of Missouri, Columbia 65211, USA.
J Anim Sci. 2004 Apr;82(4):1022-8. doi: 10.2527/2004.8241022x.
Two progestin-based protocols for the synchronization of estrus in beef cows were compared. Cyclic, nonlactating, crossbred, beef cows were assigned by age and body condition score to one of two treatments. Cows assigned to the MGA Select protocol were fed melengestrol acetate (MGA; 0.5 mg x cow(-1) x (-1)) for 14 d, GnRH was administered (100 microg i.m. of Cystorelin) 12 d after MGA withdrawal, and PGF2alpha (25 mg of i.m. Lutalyse) was administered 7 d after GnRH. Cows assigned to the 7-11 Synch protocol were fed MGA for 7 d and were injected with PG on d 7 of MGA, GnRH on d 11, and PG on d 18. Transrectal ultrasonography was performed daily to monitor follicular dynamics from the beginning of MGA feeding through ovulation after the synchronized estrus. All cows exhibited estrus in response to PG. Mean interval to estrus was shorter (P < 0.01) for 7-11 Synch-treated cows (56 +/- 1.5 h) than for cows assigned to the MGA Select protocol (73 +/- 4.7 h). Mean interval from estrus to ovulation did not differ between treatments (P > 0.10). Variances for interval to estrus differed (P < 0.01) between treatments. Mean follicular diameter at GnRH injection, PG injection, and estrus did not differ (P > 0.10) between treatments. Relative to MGA Select, serum estradiol-17beta concentrations were higher (P < 0.01) for 7-11 Synch 2 d and 1 d before, on the day of GnRH injection, in addition to 4 d after GnRH, and 24 h after PG. Mean progesterone concentrations were greater (P < 0.01) for MGA Select cows from 4 d before to 7 d after GnRH. Forty-four percent of the variation in interval to estrus between treatments was explained by differences in estradiol-17beta concentrations 24 h after PG. This study suggests that follicular competence is likely related to steroidogenic capacity of the follicle and the endocrine environment under which growth and subsequent ovulation of the dominant follicle occurs.
对两种基于孕激素的肉牛发情同步方案进行了比较。根据年龄和体况评分，将处于发情周期、非泌乳的杂交肉牛分配到两种处理之一。分配到MGA Select方案的母牛连续14天饲喂醋酸美仑孕酮（MGA；0.5毫克/头/天），撤掉MGA 12天后肌肉注射促性腺激素释放激素（GnRH，100微克的Cystorelin），GnRH注射7天后肌肉注射前列腺素F2α（25毫克的Lutalyse）。分配到7 - 11同步方案的母牛饲喂MGA 7天，在MGA处理的第7天注射PG，第11天注射GnRH，第18天注射PG。从开始饲喂MGA到同步发情后的排卵，每天进行经直肠超声检查以监测卵泡动态。所有母牛对PG均有发情反应。7 - 11同步处理的母牛发情平均间隔时间（56±1.5小时）比分配到MGA Select方案的母牛短（P<0.01）（73±4.7小时）。两种处理之间发情到排卵的平均间隔时间无差异（P>0.10）。两种处理之间发情间隔时间的方差不同（P<0.01）。两种处理之间GnRH注射、PG注射和发情时的平均卵泡直径无差异（P>0.10）。相对于MGA Select，7 - 11同步方案在GnRH注射前2天和1天、GnRH注射当天、GnRH注射后4天以及PG注射后24小时血清雌二醇-17β浓度更高（P<0.01）。从GnRH注射前4天到GnRH注射后7天，MGA Select方案母牛的平均孕酮浓度更高（P<0.01）。PG注射后24小时雌二醇-17β浓度的差异解释了两种处理之间发情间隔时间44%的变异。本研究表明，卵泡功能可能与卵泡的类固醇生成能力以及优势卵泡生长和随后排卵所处的内分泌环境有关。
