Turretfield Research Centre, South Australian Research and Development Institute, Holland Road, Rosedale, South Australia, 5350, Australia.
School of Animal and Veterinary Sciences, Roseworthy Campus, The University of Adelaide, Roseworthy, South Australia, 5371, Australia.
Theriogenology. 2023 May;202:103-109. doi: 10.1016/j.theriogenology.2023.03.008. Epub 2023 Mar 11.
This study extends observations on the effects of intra-vaginal progesterone treatment on the relationships between the time of luteolysis, emergence of the ovulatory follicle, timing of estrus and ewe fertility. Observations were made in progesterone - treated ewes in autumn, the spring equinox and late spring (Experiment 1, Data set 1) and in progesterone - treated ewes and naturally cycling ewes in autumn and the spring equinox (Experiment 1, Data set 2). In Data set 1, the day of emergence of both the first and second ovulatory follicle was positively related to the day luteal regression within each season. In turn, the day of emergence influenced the timing of estrus by means of a season by day of luteal regression interaction (P < 0.001) indicating that the relationship was positive in autumn and the spring equinox but negative in late spring. In autumn, older ovulatory follicles were associated with an earlier onset of estrus compared with younger ovulatory follicles. In late spring, this relationship was reversed and was influenced by whether or not ewes were cycling at the time of pessary insertion. In Data set 2, the relationship between the day of follicle emergence and luteal regression was influenced by a treatment by day of regression interaction indicating the relationship was positive in treated ewes and negative in naturally cycling ewes. Timing of estrus was positively related (P < 0.001) to both the day of luteal regression and the day of follicle emergence (P < 0.05), with both relationships being stronger in naturally cycling ewes than in treated ewes. In Experiment 2, pregnancy rate following artificial insemination in autumn was highest (90.2%) when luteolysis occurred during Days 7-9 of the pessary period compared with Days 1-6 (77.8%, P = 0.16), 10 to 12 (68.8%, P < 0.05) or Days ≥13 (71.2%, P < 0.05). Timing of estrus was not affected. The mean diameter of ovulatory follicles that emerged during Days 7-9 was larger on Day 12 (5.8 ± 0.13 mm) compared with other periods (range 4.7 ± 0.05 to 5.6 ± 0.14 mm). This study provides two potential strategies to improve the success of AI programs. Firstly, appropriately timed treatment with PGF2α to control the time of emergence of ovulatory follicles and, secondly, earlier treatment with eCG to improve the development of ovulatory follicles that emerge late in the pessary period. Each is likely to be influenced by season and the cyclical status of the ewe.
本研究扩展了关于阴道内孕酮治疗对黄体溶解、排卵卵泡出现、发情时间和母羊繁殖力之间关系的观察。在秋季、春分和春末（实验 1，数据集 1）以及孕酮处理母羊和自然发情母羊的秋季和春分（实验 1，数据集 2）中进行了观察。在数据集 1 中，第一个和第二个排卵卵泡出现的日期与每个季节的黄体消退日期呈正相关。反过来，发情时间又通过黄体消退日的季节与日的相互作用（P<0.001）来影响发情时间，表明这种关系在秋季和春分为正相关，但在春末为负相关。在秋季，与年轻的排卵卵泡相比，较老的排卵卵泡与发情的开始更早相关。在春末，这种关系发生了逆转，并受到放置子宫托时母羊是否发情的影响。在数据集 2 中，卵泡出现日期与黄体消退之间的关系受到治疗与消退日的相互作用的影响，表明这种关系在孕酮处理的母羊中为正相关，而在自然发情的母羊中为负相关。发情时间与黄体消退日期（P<0.001）和卵泡出现日期（P<0.05）呈正相关，且自然发情的母羊与孕酮处理的母羊相比，这两个关系都更强。在实验 2 中，与黄体溶解发生在子宫托期的第 1-6 天（77.8%，P=0.16）、第 10-12 天（68.8%，P<0.05）或第≥13 天（71.2%，P<0.05）相比，秋季人工授精后的妊娠率在黄体溶解发生在第 7-9 天最高（90.2%）。发情时间不受影响。在第 7-9 天出现的排卵卵泡的平均直径在第 12 天（5.8±0.13 mm）最大，而在其他时期则较小（范围 4.7±0.05 至 5.6±0.14 mm）。本研究提供了两种提高人工授精成功率的潜在策略。首先，适当时间用 PGF2α 处理以控制排卵卵泡出现的时间，其次，用 eCG 更早处理以改善黄体期后期出现的排卵卵泡的发育。这两种策略都可能受到季节和母羊周期性状态的影响。
