Wood S L, Lucy M C, Smith M F, Patterson D J
Department of Animal Sciences, University of Missouri, Columbia 65211, USA.
J Anim Sci. 2001 Aug;79(8):2210-6. doi: 10.2527/2001.7982210x.
The objective of this experiment was to determine the effect of a GnRH injection within a melengestrol acetate (MGA)-PGF2alpha (PGF) estrus synchronization protocol on follicular dynamics and synchronization of estrus. Pubertal crossbred beef heifers (n = 34) were randomly assigned to one of two treatments. Both treatment groups were fed MGA (0.5 mg x hd(-1) x d(-1)) for 14 d and injected (i.m.) with PGF (25 mg of Lutalyse) 19 d after MGA withdrawal. Melengestrol acetate was delivered in a feed supplement of 1.8 kg x hd(-1) x d(-1). Seventeen heifers received an injection of GnRH (100 microg Cystorelin) 12 d after MGA withdrawal and 7 d before PGF. The control group (n = 17) received only MGA-PGF. Estrus was detected four times/d for 7 d beginning on the day PGF was injected. Transrectal ultrasonography was performed daily on eight heifers from each treatment to monitor ovarian activity and characterize changes in follicular dynamics after MGA withdrawal and until ovulation after PGF. Each of the GnRH-treated heifers either ovulated or had a luteinized dominant follicle following GnRH and subsequently initiated a new follicular wave (8/8, 100%). All GnRH-treated heifers (17/17, 100%) and 94% of controls (16/17) exhibited estrus after PGF. Estrus was exhibited over a 132-h period (12 to 144 h) for control heifers compared with 60 h (48 to 108 h) for GnRH-treated heifers. The peak synchronized period for both treatments was between 48 and 72 h after PGF, during which time 76% (13/17) of the GnRH-treated heifers exhibited estrus compared with 63% (10/16) for controls. Seventy-one percent (12/17) of the GnRH-treated heifers exhibited estrus from 48 to 60 h after PGF, compared with 38% (6/16) for controls (P < 0.05). In summary, injection of GnRH within a 14- to 19-d MGA-PGF protocol increased the synchrony of estrus during the synchronized period and concentrated the period of detected estrus. This protocol may offer potential for the fixed-time insemination of replacement beef heifers.
本实验的目的是确定在醋酸美仑孕酮（MGA）-前列腺素F2α（PGF）发情同步方案中注射促性腺激素释放激素（GnRH）对卵泡动态和发情同步的影响。将青春期杂交肉用小母牛（n = 34）随机分为两种处理之一。两个处理组均饲喂MGA（0.5 mg×头-1×天-1），持续14天，并在撤掉MGA 19天后肌肉注射PGF（25 mg的氯前列醇）。醋酸美仑孕酮通过1.8 kg×头-1×天-1的饲料补充剂提供。17头小母牛在撤掉MGA 12天后且在注射PGF前7天注射GnRH（100 μg的促排3号）。对照组（n = 17）仅接受MGA-PGF处理。从注射PGF当天开始，每天检测发情4次，持续7天。对每个处理组的8头小母牛每天进行经直肠超声检查，以监测卵巢活动，并描述撤掉MGA后直至PGF注射后排卵期间卵泡动态的变化。每头经GnRH处理的小母牛在注射GnRH后要么排卵，要么有一个黄体化的优势卵泡，随后开始一个新的卵泡波（8/8，100%）。所有经GnRH处理的小母牛（17/17，100%）和94%的对照组（16/17）在注射PGF后表现出发情。对照组小母牛的发情持续132小时（12至144小时），而经GnRH处理的小母牛为60小时（48至108小时）。两种处理的同步高峰期均在注射PGF后的48至72小时之间，在此期间，76%（13/17）的经GnRH处理的小母牛表现出发情，而对照组为63%（10/16）。71%（12/17）的经GnRH处理的小母牛在注射PGF后的48至60小时表现出发情，而对照组为38%（6/16）（P < 0.05）。总之，在14至19天的MGA-PGF方案中注射GnRH可提高同步期内发情的同步性，并使检测到发情的时间段集中。该方案可能为后备肉用小母牛的定时输精提供潜力。
