DATA

The current study was conducted on 663 cyclic lactating Holstein cows in one of the industrial farms near Qazvin province, Iran, from June 2119 to September 2020. We investigated the effects of equine chorionic gonadotropin (eCG) hormone administration 80 h before the implementation of the Ovsynch and fixed-time artificial insemination (OVS+FTAI) program in the form of the G6G protocol on pregnancy rate and reproductive parameters of dairy cows in the first postpartum insemination under heat stress conditions. The cows under study were randomly assigned to one of the following protocols and received the following treatments: G6G (PGF2α-2d-GnRH-6d-OVS+FTAI(GnRH(GnRH1)-7d-PGF2α(PG)-56h-GnRH-18h-FTAI, n = 213), 300e+G6G (PGF2α-2d-GnRH-64h-300IU,eCG-80h-OVS+FTAI, n = 231), and 500e+G6G (PGF2α-2d-GnRH-64h-500IU,eCG-80h-OVS+FTAI, n = 219). The overall pregnancy rates of cows in the G6G, 300e+G6G, and 500e+G6G protocols were 29.5 ± 0.03%, 33.7 ± 0.03%, and 35.6 ± 0.03%, respectively. The 500e+G6G protocol increased the pregnancy rate of cows with a BCS ≤ 2.5 compared to the G6G protocol (p = 0.04). The 500e+G6G protocol significantly increased the pregnancy rate of cows that produced > 34 kg milk per day compared to the G6G protocol (p = 0.03). In conclusion, using 500 IU, eCG 80 h before the implementation of the OVS+FTAI program in the form of G6G protocol had beneficial effects on increasing the pregnancy rate of cows that had a BCS ≤ 2.5 or produced > 34 kg milk per day compared to the G6G protocol under heat stress conditions.

本研究于2019年6月至2020年9月，在伊朗加兹温省附近的某工业化养殖农场开展，受试对象为663头循环泌乳荷斯坦奶牛。本研究旨在探究热应激条件下，于Ovsynch定时人工授精（Ovsynch and fixed-time artificial insemination, OVS+FTAI）方案实施前80小时施加马绒毛膜促性腺激素（equine chorionic gonadotropin, eCG）并采用G6G方案，对奶牛产后首次授精的妊娠率及繁殖参数的影响。受试奶牛被随机分为以下三组并接受对应处理：G6G组（方案流程：前列腺素F2α(PGF2α)-2天-促性腺激素释放激素(GnRH)-6天-OVS+FTAI[GnRH(GnRH1)-7天-PGF2α(PG)-56小时-GnRH-18小时-授精]，n=213）、300e+G6G组（方案流程：PGF2α-2d-GnRH-64小时-300国际单位eCG-80小时-OVS+FTAI，n=231）以及500e+G6G组（方案流程：PGF2α-2d-GnRH-64小时-500国际单位eCG-80小时-OVS+FTAI，n=219）。G6G组、300e+G6G组及500e+G6G组奶牛的总体妊娠率分别为29.5±0.03%、33.7±0.03%及35.6±0.03%。相较于G6G组，500e+G6G组可提升体况评分（Body Condition Score, BCS）≤2.5的奶牛的妊娠率（P=0.04）；同时，相较于G6G组，500e+G6G组可显著提升日均产奶量＞34kg的奶牛的妊娠率（P=0.03）。综上，在热应激条件下，于G6G方案的OVS+FTAI程序实施前80小时使用500IU eCG，相较于单纯G6G方案，可有效提升体况评分≤2.5或日均产奶量＞34kg的奶牛的妊娠率。