North Florida Research and Education Center, University of Florida, Marianna, FL 32446, USA
J Anim Sci. 2011 Oct;89(10):3030-9. doi: 10.2527/jas.2010-3455. Epub 2011 Apr 29.
Two experiments were conducted to evaluate whether hCG administered 7 d before initiating the CO-Synch + controlled internal drug release (CIDR) ovulation synchronization protocol (Exp. 1 and 2), or replacing GnRH with hCG at the time of AI (Exp. 1), would improve fertility to a fixed-time AI (TAI) in suckled beef cows. In addition, the effects of hCG on follicle dynamics, corpus luteum development, and concentrations of progesterone (P4) were evaluated. In Exp. 1, cows were stratified by days postpartum, age, and parity and assigned randomly to a 2 × 2 factorial arrangement of 4 treatments: 1) cows received 100 µg of GnRH at CIDR insertion (d -7) and 25 mg of PGF(2α) at CIDR removal (d 0), followed in 64 to 68 h by a TAI plus a second injection of GnRH at TAI (CG; n = 29); 2) same as CG but the second injection of GnRH at the time of insemination was replaced by hCG (CH; n = 28); 3) same as CG, but cows received hCG 7 d (d -14) before CIDR insertion (HG; n = 28); and 4) same as HG, but cows received hCG 7 d (d -14) before CIDR insertion (HH; n = 29). Pregnancy rates were 52, 41, 59, and 38% for GG, GH, HG, and HH, respectively. Cows receiving hCG (39%) in place of GnRH at TAI tended (P = 0.06) to have poorer pregnancy rates than those receiving GnRH (56%). Pre-CO-Synch hCG treatment increased (P < 0.05) the percentage of cows with concentrations of P4 >1 ng/mL at d -7, increased (P < 0.02) concentration of P4 on d -7, and decreased (P < 0.001) the size of the dominant follicle on d 0 and 3, compared with cows not treated with hCG on d -14. In Exp. 2, cows were stratified based on days postpartum, BCS, breed type, and calf sex and then assigned to the CG (n = 102) or HG (n = 103) treatments. Overall pregnancy rates were 51%, but no differences in pregnancy rates were detected between treatments. Pre-CO-Synch hCG treatment increased (P < 0.05) the percentage of cows cycling on d -7 and increased (P < 0.05) concentrations of P4 on d -7 compared with pre-CO-Synch controls. Therefore, pretreatment induction of ovulation after hCG injection 7 d before initiation of CO-Synch + CIDR protocol failed to enhance pregnancy rates, but replacing GnRH with hCG at the time of AI may reduce pregnancy rates.
进行了两项实验，以评估在开始 CO-Synch + 控制内部药物释放 (CIDR) 排卵同步方案前 7 天给予 hCG（实验 1 和 2），或在 AI 时用 hCG 替代 GnRH（实验 1）是否会提高哺乳期肉牛的定时 AI（TAI）受孕率。此外，还评估了 hCG 对卵泡动态、黄体发育和孕酮（P4）浓度的影响。在实验 1 中，根据产后天数、年龄和胎次对牛进行分层，并随机分配到 4 种处理的 2×2 因子排列：1）CIDR 插入时（d-7）给予 100 µg GnRH 和 CIDR 去除时（d 0）给予 25 mg PGF2α，然后在 64 至 68 小时内进行 TAI 加 TAI 时的第二次 GnRH 注射（CG；n=29）；2）与 CG 相同，但在 AI 时用 hCG 替代第二次 GnRH 注射（CH；n=28）；3）与 CG 相同，但在 CIDR 插入前 7 天（d-14）给予 hCG（HG；n=28）；4）与 HG 相同，但在 CIDR 插入前 7 天（d-14）给予 hCG（HH；n=29）。GG、GH、HG 和 HH 的妊娠率分别为 52%、41%、59%和 38%。在 TAI 时用 hCG（39%）代替 GnRH 的牛的妊娠率（P=0.06）倾向于低于接受 GnRH（56%）的牛。预 CO-Synch hCG 处理增加（P<0.05）了 d-7 时 P4 浓度>1ng/mL 的牛的比例，增加（P<0.02）了 d-7 时 P4 的浓度，并降低（P<0.001）了 d-0 和 3 时的主导卵泡大小与 d-14 时未接受 hCG 处理的牛相比。在实验 2 中，根据产后天数、BCS、品种类型和犊牛性别对牛进行分层，然后分配到 CG（n=102）或 HG（n=103）处理。总妊娠率为 51%，但处理之间未检测到妊娠率差异。预 CO-Synch hCG 处理增加（P<0.05）了 d-7 时发情的牛的比例，并增加（P<0.05）了 d-7 时 P4 的浓度与预 CO-Synch 对照组相比。因此，在开始 CO-Synch + CIDR 方案前 7 天给予 hCG 注射以诱导排卵预处理未能提高妊娠率，但在 AI 时用 hCG 替代 GnRH 可能会降低妊娠率。
