Instituto de Reproducción Animal Uruguay, Fundación IRAUy, Montevideo, Uruguay; Programa de Posgrado de la Facultad de Veterinaria, Universidad de la República, Montevideo, Uruguay.
Instituto de Reproducción Animal Córdoba (IRAC), Córdoba, Argentina; Instituto A.P. de Ciencias Básicas y Aplicadas, Medicina Veterinaria, Universidad Nacional de Villa María, Villa del Rosario, Córdoba, Argentina.
Theriogenology. 2022 Mar 15;181:1-7. doi: 10.1016/j.theriogenology.2021.12.028. Epub 2021 Dec 31.
This study evaluated the relationship between proestrus length and follicular size, estrous behavior, and pregnancy rate in Bos taurus beef heifers subjected to fixed-time artificial insemination (FTAI). A total of 911 heifers received a synchronization treatment protocol for FTAI (J-Synch) consisting of an intravaginal progesterone device for 6 d, estradiol benzoate at the time of device insertion cloprostenol sodium and eCG at device removal and GnRH at the time of FTAI. The presence or absence of a corpus luteum (CL) was determined by ultrasonography at device insertion and all heifers were tail painted at device removal for estrus detection at the time of FTAI. For the establishment of different periods of proestrus length (i.e., interval from device removal to FTAI), GnRH was administered i.m. at 48 h (n = 308), 60 h (n = 290) or 72 h (n = 313) after device removal. The diameter of the largest follicle at the time of GnRH administration was determined by ultrasonography, expression of estrous was determined by percentage of tail paint removal, and FTAI was performed at the time of GnRH administration in all heifers. The diameter of the largest follicle was greater when GnRH/FTAI was performed at 72 or 60 h (12.9 ± 0.2 mm and 12.8 ± 0.1 mm, respectively) than at 48 h (12.2 ± 0.1 mm, P < 0.05). The proportion of heifers in estrus tended to be greater when GnRH/FTAI was performed at 72 h (77.0%, 137/178) than at 48 h (68.2%, 122/179; P = 0.06), and intermediate at 60 h (71.4%, 120/168). Pregnancy rate tended to be greater in heifers with the longest (72 h: 70.0%, 219/313) than the shortest (48 h: 63.6%, 196/308; P < 0.1) proestrus length, while 60 h proestrus length was intermediate (63.1%, 183/290; P= NS). Pregnancy rate was affected by the presence of a CL at device insertion (71.3%, 352/494 in heifers with a CL, vs. 59.0%, 246/417 for those without a CL; P < 0.01). For those heifers bearing a CL, pregnancy rate was greater in heifers with a 72 h proestrus length (77.0%, 134/174) than with 48 or 60 h proestrus length (67.7%, 107/158 and 68.5%, 111/162; respectively; P < 0.05). In heifers without a CL, proestrus length did not affect pregnancy rate. In summary, extending proestrus length by delaying the interval from device removal to GnRH/FTAI from 48 to 72 h, was associated with a greater diameter of the preovulatory follicle, greater proportion of heifers expressing estrus at the time of FTAI, and greater pregnancy rate in cycling beef heifers.
本研究评估了固定时间人工授精（FTAI）中发情前期长度与卵泡大小、发情行为和妊娠率之间的关系。共有 911 头小母牛接受了 J-Synch 的同步处理方案，包括阴道内孕酮装置 6 天，在装置插入时给予苯甲酸雌二醇，氯前列醇钠和 eCG 在装置去除时，在 FTAI 时给予 GnRH。在装置插入时通过超声确定黄体（CL）的存在与否，并且所有小母牛在装置去除时都尾巴涂漆，以便在 FTAI 时检测发情。为了建立不同的发情前期长度（即从装置去除到 FTAI 的间隔），在装置去除后 48 小时（n = 308）、60 小时（n = 290）或 72 小时（n = 313）时肌肉内给予 GnRH。在 GnRH 给药时通过超声确定最大卵泡的直径，通过尾巴涂漆去除的百分比确定发情表达，并且在所有小母牛中在 GnRH 给药时进行 FTAI。当 GnRH/FTAI 在 72 或 60 小时（12.9 ± 0.2mm 和 12.8 ± 0.1mm，分别）时进行时，最大卵泡的直径大于 48 小时（12.2 ± 0.1mm，P < 0.05）。当 GnRH/FTAI 在 72 小时（77.0%，137/178）时发情的小母牛比例趋于更高，而在 48 小时（68.2%，122/179；P = 0.06）时，中间在 60 小时（71.4%，120/168）。发情前期长度最长的小母牛（72 小时：70.0%，219/313）的妊娠率趋于更高，而最短的小母牛（48 小时：63.6%，196/308；P < 0.1），而 60 小时发情前期长度为中间（63.1%，183/290；P = NS）。妊娠率受装置插入时 CL 的存在影响（71.3%，352/494 有 CL 的小母牛，与没有 CL 的小母牛 59.0%，246/417；P < 0.01）。对于有 CL 的小母牛，发情前期长度为 72 小时（77.0%，134/174）的小母牛的妊娠率高于 48 或 60 小时（67.7%，107/158 和 68.5%，111/162；分别；P < 0.05）。对于没有 CL 的小母牛，发情前期长度不影响妊娠率。总之，通过将从装置去除到 GnRH/FTAI 的间隔从 48 小时延长到 72 小时，延长发情前期长度与更大的排卵前卵泡直径、更多的发情行为以及循环肉牛小母牛的更高妊娠率相关。
