Morel M C G Davies, Newcombe J R, Reynolds N
Institute of Biological, Environmental and Rural Sciences, Aberystwyth University, Ceredigion SY23 3AL, UK.
Equine Fertility Clinic, Warren House Veterinary Centre, Warren House Farm, Barracks Lane, Brownhills, West Midlands WS8 6LS, UK.
Vet Rec. 2015 Mar 21;176(12):310. doi: 10.1136/vr.102308. Epub 2015 Jan 23.
The mare's reproductive system is rarely capable of sustaining multiple pregnancies to term. Multiple pregnancies largely derive from multiple ovulations, most commonly double ovulations, hence, double ovulations are of significant concern to breeders/veterinarians. Double ovulations may be synchronous or asynchronous. Asynchrony of up to 96 hours may result in two embryonic vesicles of very different sizes, which are challenging to detect at early ultrasonic pregnancy detection. This study aims to (1) document the incidence of synchronous and asynchronous double ovulation and (2) determine whether this varies with month/season. 506 cycles from double ovulating mares were monitored at 8±1 hour intervals before expected ovulation until 96 hours post initial ovulation. Mares were grouped according to eight-hour ovulation intervals and month/season. When asynchrony was classed as greater than or equal to eight hours or greater than or equal to 24 hours apart, respectively, a significant (P<0.001) difference existed between the number of mares demonstrating asynchronous double ovulations (65.8 and 28.5 per cent) and synchronous double ovulations (34.2 and 71.5 per cent). Significantly (P<0.05), more asynchronous ovulations occurred in the seasonal transition periods. This study demonstrates that asynchronous double ovulation is common and emphasises the importance of closely monitoring mares, particularly at the extremes of the breeding season, for double ovulation up to or at 96 hours postinitial ovulation in order to minimise the chances of missing multiple pregnancy.
母马的生殖系统很少能够维持多胎妊娠至足月。多胎妊娠大多源于多次排卵，最常见的是双排卵，因此，双排卵是育种者/兽医非常关注的问题。双排卵可能是同步的，也可能是异步的。长达96小时的不同步可能导致两个大小差异很大的胚胎囊泡，这在早期超声妊娠检测中很难被发现。本研究旨在：（1）记录同步和异步双排卵的发生率；（2）确定其是否随月份/季节而变化。对双排卵母马的506个发情周期在预期排卵前每隔8±1小时进行监测，直至首次排卵后96小时。母马根据8小时的排卵间隔以及月份/季节进行分组。当不同步分别被分类为间隔大于或等于8小时或大于或等于24小时时，出现异步双排卵的母马数量（分别为65.8%和28.5%）与同步双排卵的母马数量（分别为34.2%和71.5%）之间存在显著差异（P<0.001）。在季节转换期，显著（P<0.05）出现更多的异步排卵。本研究表明，异步双排卵很常见，并强调了密切监测母马的重要性，尤其是在繁殖季节的极端时期，要监测首次排卵后直至96小时的双排卵情况，以尽量减少错过多胎妊娠的几率。
