Instituto de Reproducción Animal Uruguay, Fundación IRAUy, Montevideo, Uruguay; Programa de Posgrado de la Facultad de Veterinaria, Universidad de la República, Montevideo, Uruguay.
Programa de Posgrado de la Facultad de Veterinaria, Universidad de la República, Montevideo, Uruguay; Laboratorio de Endocrinología y Metabolismo Animal, Facultad de Veterinaria, Universidad de la República, Montevideo, Uruguay.
Theriogenology. 2020 Jul 15;151:16-27. doi: 10.1016/j.theriogenology.2020.03.031. Epub 2020 Mar 28.
The objective of the present study was to evaluate the effect of equine chorionic gonadotropin (eCG) administration associated to different proestrus lengths for Fixed-time AI (FTAI) in beef heifers. In Experiment 1, pre-pubertal heifers (n = 46) received a 6-day estradiol/progesterone-based treatment (J-Synch protocol), and were then allocated into four experimental groups in a 2 × 2 factorial design, to receive or not receive eCG (300 IU) at the time of intravaginal progesterone device removal, and to receive GnRH at 48 h or 72 h after device removal (to induce shortened and prolonged proestrus length, respectively). Endometrial samples were obtained 6 d after ovulation from the cranial portion of the uterine horn. The eCG administration induced greater serum estradiol-17β concentrations before ovulation (P < 0.05) and greater proportion of heifers bearing a competent corpus luteum after ovulation (P = 0.054). Delaying GnRH administration from 48 h to 72 h induced a longer interval from device removal to ovulation (i.e., prolonged proestrus; P < 0.05), larger diameter of the ovulatory follicle, and greater progesterone concentrations on Day 10-11 after ovulation. Heifers in eCG + GnRH72h group had more uterine receptors in luminal epithelium than those in eCG + GnRH48h group (PR and ERα), and than those in No eCG + GnRH72h group (PR) (P < 0.05). No effect of eCG or GnRH treatments was found in endometrial gene expression of progesterone and estrogen receptors. In Experiment 2, a total of 2,598 heifers received the J-Synch protocol associated or not with eCG administration at device removal, followed by FTAI/GnRH at 60 or 72 h after device removal (i.e., prolonged proestrus protocol). Heifers that received eCG had greater P/AI than those not receiving eCG (P < 0.05) and there was an interaction between eCG treatment and time of FTAI. The lowest P/AI was found in those heifers that received FTAI/GnRH at 72 h without eCG treatment at device removal (P < 0.05), and no differences were found between the other experimental groups. In conclusion, prolonging the length of proestrus in J-Synch protocol improves ovulatory follicular diameter and luteal function; and the administration of eCG at device removal improves preovulatory estradiol concentrations and luteal function. Finally, P/AI was enhanced by eCG treatment and the improvement was more evident when FTAI/GnRH was performed at 72 h after device removal.
本研究的目的是评估在牛小母牛中，发情诱导（FTAI）前不同发情期长度与使用马绒毛膜促性腺激素（eCG）联合使用的效果。在实验 1 中，未成熟的小母牛（n=46）接受 6 天的雌二醇/孕酮为基础的处理（J-Synch 方案），然后根据 2×2 析因设计，将它们分为四个实验组，分别为在阴道内孕酮装置取出时是否接受 eCG（300 IU）以及在装置取出后 48 小时或 72 小时是否接受 GnRH（分别诱导缩短和延长发情期长度）。在排卵后 6 天，从小母牛子宫角的头部获得子宫内膜样本。与排卵前（P<0.05）相比，eCG 处理诱导了更高的血清雌二醇-17β浓度，并且排卵后具有更有能力的黄体的小母牛比例更高（P=0.054）。将 GnRH 给药从 48 小时延迟到 72 小时诱导了从装置移除到排卵的时间间隔更长（即延长发情期；P<0.05），排卵卵泡的直径更大，排卵后第 10-11 天的孕酮浓度更高。eCG+GnRH72h 组的小母牛在腔上皮中的子宫受体数量多于 eCG+GnRH48h 组（PR 和 ERα），也多于 No eCG+GnRH72h 组（PR）（P<0.05）。eCG 或 GnRH 处理对子宫内膜孕激素和雌激素受体的基因表达没有影响。在实验 2 中，共有 2598 头小母牛接受 J-Synch 方案与或不与装置取出时的 eCG 联合使用，随后在装置取出后 60 或 72 小时进行 FTAI/GnRH（即延长发情期方案）。接受 eCG 的小母牛的配种率高于未接受 eCG 的小母牛（P<0.05），并且 eCG 处理和 FTAI 时间之间存在相互作用。在没有在装置移除时接受 eCG 处理的情况下，在 72 小时进行 FTAI/GnRH 的小母牛中发现了最低的配种率（P<0.05），而其他实验组之间没有差异。总之，在 J-Synch 方案中延长发情期长度可以改善排卵卵泡的直径和黄体功能；并且在装置移除时给予 eCG 可以提高促排卵前的雌二醇浓度和黄体功能。最后，通过 eCG 处理提高了配种率，当在装置移除后 72 小时进行 FTAI/GnRH 时，改善更为明显。
