Effect of gonadotropin-releasing hormone administered at the time of artificial insemination for cows detected in estrus by conventional estrus detection or an automated activity-monitoring system

摘要

The objectives of this study were to determine the ef-fects of GnRH at the time of artificial insemination (AI) on ovulation, progesterone 7 d post-AI, and pregnancy in cows detected in estrus using traditional methods (tail chalk removal and mount acceptance visualiza-tion) or an automated activity-monitoring (AAM) system. We hypothesized that administration of GnRH at the time of AI would increase ovulation rate, plasma progesterone post-AI, and pregnancy per AI (P/AI) in cows detected in estrus. In experiment 1, Holstein cows (n = 398) were blocked by parity and randomly assigned to receive an injection of GnRH at the time of estrus detection/AI (GnRH, n = 197) or to remain un-treated (control, n = 201) on 4 farms. The GnRH was administered as 100 mu g of gonadorelin acetate. Ovarian structures and plasma progesterone were assessed in a subset of cows (GnRH, n = 52; control, n = 55) in experiment 1 at the time of AI and 7 d later. In ex-periment 2, a group of 409 cows in an AAM farm were enrolled as described for experiment 1 (GnRH, n = 207; control, n = 202). Data were categorized for parity (primiparous vs. multiparous), season (cool vs. warm), number of services (first vs. > first), DIM (>150 DIM vs. <= 150 DIM), and for AAM cows in experiment 2 for activity level (high: 90-100 index vs. low: 35-89 index). Pregnancy diagnosis was performed between 32 and 45 d post-AI (P1) and 60 to 115 d post-AI (P2). In experi-ment 1, there was no difference in plasma progesterone at day of estrus detection (control = 0.09 ng/mL vs. GnRH = 0.16 ng/mL), 7 d later (control = 2.03 ng/mL vs. GnRH = 2.18 ng/mL), and ovulation rate (GnRH = 83.2 vs. control = 77.9) between treatments. There were no effects of GnRH in experiment 1 for P/AI at P1 (control = 43.3 vs. GnRH = 38.6), P2 (control = 38.4 vs. GnRH = 34.5), and for pregnancy loss (control = 9.8 vs. GnRH = 8.2). In experiment 2, there were no effects of GnRH for P/AI at P1 (control = 39.6 vs. GnRH = 40.1), P2 (control = 35.0 vs. GnRH = 37.4), and for pregnancy loss (control = 9.5 vs. GnRH = 6.2). There was a tendency for a parity effect on P/AI for P1, but not P2 or for preg-nancy loss. High-activity cows had greater P/AI in P1 (low activity = 27.9 vs. high activity = 44.1), P2 (low activity = 21.8 vs. high activity = 41.2), and lower pregnancy loss (low activity = 20.7 vs. high ac-tivity = 5.1), but there were no interactions between treatment and activity level. The current study did not support the use of GnRH at estrus detection to improve ovulatory response, progesterone 1 wk post-AI, and P/ AI. More research is needed to investigate the relation-ship between GnRH at the time of AI and activity level in herds using AAM systems.