Reproductive success of Thoroughbred mares and stallions
As Ireland is the third largest producer of thoroughbred horses worldwide, keeping track of the thoroughbred reproductive performance is almost mandatory. Irish researchers conducted a large-scale study looking at the effects of a variety of mare and stallion factors on per-cycle pregnancy rate (PCPR) and pregnancy loss in a large population of Thoroughbreds.
A number of mare factors were evaluated, including mare age, reproductive status, month of foaling, dystocia, month of cover, foal heat, cycle number, treatments, walk-in status. Stallion factors were also looked at, including stallion identity, age, shuttle status, time elapsed between covers and high stallion usage on the per cycle pregnancy rate and pregnancy loss.
In mares, advancing age showed a significant decrease in pregnancy rate - geriatric mares (18 or older) were 2.9 times less likely to become pregnant than mares 8 and under; also, geriatric mares were 2.6 times more likely to lose the pregnancy. Barren mares were 1.8 times more likely to lose a pregnancy than maiden mares. Mares bred on foal heat (less than 20 days from foaling) also showed a significant decrease in PCPR. Whether the mare had been diagnosed with and treated for a uterine problem showed no effect on PCPR.
In stallions the study found that there was no difference in PCPR whether the mare was the first one bred by a stallion on a given day or the fourth. There was also no difference in PCPR whether the stallion shuttled between hemispheres. However, high-usage stallions that had bred more than 21 times in a seven-day period had a 10% decrease in PCPR.
In conclusion, these study results show mare age exerted the greatest influence on fertility. Old age and cover within 20 days post-partum were associated with the lowest pregnancy rates. However, Thoroughbreds can be effectively managed to achieve high reproductive performance in a commercial setting.
> From: Lane et al., Reprod Dom Anim 51 (2016) 181-187. All rights reserved to Blackwell Verlag GmbH. Click here for the online summary.
