Fertility of Shetland pony stallions used in different breeding systems: a retrospective study.

In horses reproductive performance is usually expressed as the foaling rate. This rate ranges from 40% to 80%. Three major factors contribute to this variation namely, the stallion, the mare and management. In this study, the performance of Shetland ponies kept in three different breeding systems was investigated retrospectively. In one breeding system, the stud farmer travelled with his stallion (n = 9) to the mare (system 1) while in another system, the stallion (n = 3) stayed at the stud farm and the mares came to the stallion (system 2). The last system was pasture breeding (system 3; n = 9). Each stallion participated in only one system. The average number of cycles per mare used for breeding did not differ significantly between systems 1 and 2. However, the number of matings per cycle was higher in system 2 than in system 1. The average number of mares serviced per stallion was 91, 50, and 17 for systems 1, 2 and 3, respectively. Mares mated in pasture had a 2.8-fold higher chance (p < 0.05) of having a foal the next season than the mares mated under systems 1 and 2. The foaling rate per season was 58%, 48%, and 80% for systems 1, 2 and 3, respectively. Management aspects play an important role in the relatively low foaling percentages of systems 1 and 2.