Cedeño Andrés V, Cuervo Rodrigo, Tríbulo Andrés, Tríbulo Ricardo, Andrada Salvador, Mapletoft Reuben, Menchaca Alejo, Bó Gabriel A
Instituto de Reproducción Animal Córdoba (IRAC), Zona Rural General Paz, 5145, Córdoba, Argentina; Maestría en Reproducción Bovina, Facultad de Ciencias Agropecuarias, Universidad Nacional de Córdoba, Argentina; Laboratorio de Biotecnología de La Reproducción Animal, Medicina Veterinaria, Escuela Superior Politécnica Agropecuaria de Manabí Manuel Félix López (ESPAM-MFL) Bolívar, Manabí, Ecuador.
Maestría en Reproducción Bovina, Facultad de Ciencias Agropecuarias, Universidad Nacional de Córdoba, Argentina; Instituto de Ciencias Básicas, Medicina Veterinaria, Universidad Nacional de Villa María, Villa Del Rosario, Córdoba, Argentina.
Theriogenology. 2021 Feb;161:294-300. doi: 10.1016/j.theriogenology.2020.12.014. Epub 2020 Dec 15.
Three experiments evaluated the effects of expression of estrus and gonadotropin releasing hormone (GnRH) treatment on pregnancies per AI (P/AI) in beef cattle that were treated with an estradiol/progesterone (P4)-based protocol for fixed-time artificial insemination (FTAI). In Experiment 1, 20 non-lactating beef cows were treated with 2 mg estradiol benzoate (EB) and an intravaginal device containing 0.5 g of P4. Seven days later, P4 devices were removed and all cows received prostaglandin F2 alpha (PGF) and 0.5 mg estradiol cypionate (ECP). Estrus was detected using tail paint and cows that did not show estrus by 48 h after P4 device removal were randomized to receive GnRH or no treatment. Ovulation, as determined by ultrasonography, occurred earlier in cows that showed estrus (68.0 ± 2.5 h) than in cows that did not (82.0 ± 2.1 h, P < 0.05). Furthermore, cows that received GnRH ovulated earlier (78.0 ± 2.6 h) than those that did not (86.0 ± 2.0, P < 0.05). Experiment 2 determined whether expression of estrus and the administration of GnRH to animals that did not show estrus increased P/AI. Non-lactating beef cows and heifers (n = 1356) were treated as in Experiment 1 (P4 device removal, PGF2α and ECP administration on Day 7) or extended until Day 8. All animals in estrus by 48 h after P4 device removal were inseminated and those not showing estrus received GnRH or no treatment and were FTAI 8 h later (i.e., at 56 h). P/AI were greater (P < 0.01) in animals that were observed in estrus by 48 h (56.4%) than in those that did not show estrus (46.5%). Likewise, animals that did not show estrus but were treated with GnRH had greater P/AI (53.8%, P < 0.04) than those that did not receive GnRH (37.9%). Experiment 3 was designed to determine the effect of delaying GnRH treatment to the time of FTAI (at 56 h) in cows not showing estrus by 48 h after P4 device removal. Suckled beef cows (n = 969) were treated as in Experiment 1, except that all cows also received 400 IU of eCG at the time of P4 device removal on Day 7. Cows that showed estrus by 48 h or 56 h had greater P/AI (62.3%, P < 0.05) than those did not show estrus (51.5%). Furthermore, when cows that did not show estrus by 48 h were analyzed separately, P/AI were greater (P < 0.05) in those that received GnRH at 48 h and were FTAI by 56 h (64.9%) than in those that received GnRH concurrent with FTAI by 56 h after device removal (54.6%). In summary, expression of estrus was associated with earlier ovulations and resulted in greater P/AI in cows and heifers treated with an estradiol/P4-based protocol for FTAI. Furthermore, GnRH treatment in animals that did not show estrus hastened the time of ovulation and increased P/AI.
三项实验评估了发情表现和促性腺激素释放激素（GnRH）处理对采用基于雌二醇/孕酮（P4）方案进行定时人工授精（FTAI）的肉牛每人工授精妊娠数（P/AI）的影响。在实验1中，20头非泌乳肉牛母牛接受了2毫克苯甲酸雌二醇（EB）和一个含有0.5克P4的阴道内装置处理。7天后，取出P4装置，所有母牛接受前列腺素F2α（PGF）和0.5毫克环丙孕酮（ECP）。使用尾漆检测发情情况，在取出P4装置后48小时内未表现出发情的母牛被随机分组，分别接受GnRH处理或不接受处理。通过超声检查确定，表现出发情的母牛排卵时间更早（68.0±2.5小时），而未发情的母牛排卵时间为（82.0±2.1小时，P<0.05）。此外，接受GnRH处理的母牛排卵时间更早（78.0±2.6小时），而未接受处理的母牛排卵时间为（86.0±2.0小时，P<0.05）。实验2确定了对未表现出发情的动物进行发情表现和GnRH给药是否会增加P/AI。非泌乳肉牛母牛和小母牛（n = 1356）的处理方式与实验1相同（取出P4装置，在第7天给予PGF2α和ECP），或延长至第8天。在取出P4装置后48小时内表现出发情的所有动物都进行了人工授精，未表现出发情的动物接受GnRH处理或不接受处理，并在8小时后（即56小时）进行FTAI。在48小时内观察到发情的动物的P/AI（56.4%）高于未表现出发情的动物（46.5%，P<0.01）。同样，未表现出发情但接受GnRH处理的动物的P/AI（53.8%，P<0.04）高于未接受GnRH处理的动物（37.9%）。实验3旨在确定在取出P4装置后48小时内未表现出发情的母牛中将GnRH处理推迟到FTAI时间（56小时）的影响。哺乳肉牛母牛（n = 969）的处理方式与实验1相同，不同之处在于所有母牛在第7天取出P4装置时还接受了400国际单位的eCG。在48小时或56小时内表现出发情的母牛的P/AI（62.3%，P<0.05）高于未表现出发情的母牛（51.5%）。此外，当分别分析在48小时内未表现出发情的母牛时，在48小时接受GnRH并在56小时进行FTAI的母牛的P/AI（64.9%）高于在取出装置后56小时与FTAI同时接受GnRH的母牛（54.6%，P<0.05）。总之，发情表现与更早的排卵相关，并导致采用基于雌二醇/P4方案进行FTAI处理的母牛和小母牛的P/AI更高。此外，对未表现出发情的动物进行GnRH处理可加快排卵时间并增加P/AI。
