Mikeska J C, Williams G L
Beef Cattle Reproduction Lab. Texas Agricultural Experiment Station, Beeville 78102.
J Anim Sci. 1988 Apr;66(4):939-46. doi: 10.2527/jas1988.664939x.
The purpose of these studies was to investigate the pattern and timing of preovulatory endocrine events, estrus and ovulation in Brahman X Hereford (F1) heifers synchronized with norgestomet and estradiol valerate. In Exp. 1, 66 nulliparous and 191 primiparous Brahman X Hereford (F1) heifers were used to estimate the interval from norgestomet implant removal to onset of estrus. The mean interval from implant removal to onset of estrus was 29.8 +/- .5 h, with 80.9% exhibiting estrus within 48 h. Endocrine and reproductive characteristics were examined in detail during Exp. 2 with 37 primiparous heifers. Continuous observation for estrus, 6-h or 2-h blood sampling and ovarian palpation per rectum were employed. All animals were artificially inseminated 48 h after implant removal. Mean interval from implant removal to onset of estrus and to onset of the luteinizing hormone (LH) surge were closely related (r = .91; P less than .0001). Mean intervals from implant removal to ovulation, onset of estrus to ovulation and onset of LH surge to ovulation were 59.1 +/- 2.5 h, 23.3 +/- 1.4 h and 23.1 +/- 1.6 h, respectively. Approximately 73% of heifers exhibited estrus within 54 h after implant removal (optimal timing); conception rate was 59.3% in this subgroup. Conception rate of heifers that did not exhibit estrus within 54 h after implant removal or exhibited an LH surge later than 12 h after estrus (delayed timing) was 10%. Assessment of plasma estradiol-17 beta concentrations suggested that retarded selection and(or) maturation of the preovulatory follicle following implant removal delayed estrus and lowered conception in up to 28% of females timed-inseminated at 48 h.
这些研究的目的是调查经诺孕美特和戊酸雌二醇同步处理的婆罗门×赫里福德（F1）小母牛排卵前内分泌事件、发情和排卵的模式及时间。在实验1中，使用66头未生育和191头初产的婆罗门×赫里福德（F1）小母牛来估计从取出诺孕美特植入物到发情开始的间隔时间。从取出植入物到发情开始的平均间隔时间为29.8±0.5小时，80.9%的母牛在48小时内发情。在实验2中，对37头初产小母牛详细检查了内分泌和生殖特征。采用连续观察发情、每6小时或2小时采集血样以及经直肠触诊卵巢。所有动物在取出植入物后48小时进行人工授精。从取出植入物到发情开始以及到促黄体生成素（LH）峰开始的平均间隔时间密切相关（r = 0.91；P＜0.0001）。从取出植入物到排卵、从发情开始到排卵以及从LH峰开始到排卵的平均间隔时间分别为59.1±2.5小时、23.3±1.4小时和23.1±1.6小时。大约73%的小母牛在取出植入物后54小时内发情（最佳时间）；该亚组的受孕率为59.3%。在取出植入物后54小时内未发情或在发情后12小时后出现LH峰（延迟时间）的小母牛的受孕率为10%。血浆雌二醇-17β浓度评估表明，取出植入物后排卵前卵泡的选择和（或）成熟延迟，导致高达28%在48小时定时输精的雌性发情延迟且受孕率降低。
