Ovulatory Failure in Mares During Breeding Seasons

Abstract In the years 2022 and 2023 we investigated the prevalence of the ovulatory failure in 133 mares of different breed, 3 to 24 years old, brought to the Equine clinic of the University of Veterinary Medicine and Pharmacy (UVMP) in Košice. Our research involved the monitoring of the reproduction cycle in these mares with the aim to determine the prevalence of ovulatory failure during the breeding season, focusing on certain specific parameters that were considered sufficiently relevant with respect to the development of such failure. These parameters included environmental temperature and the amount of daylight the mares were exposed to, attributable to the months of the breeding season. In addition, we also evaluated the size of pre-ovulatory follicles and the influence of age of the investigated mares. During the mentioned years, one of the ovulatory failures occurred in 17 out of 133 mares (12.78 %). Examination by ultrasonography (USG) and the subsequent analysis of the occurrence of failures in relation to the investigated parameters allowed us to conclude that the length of daylight, age, and environmental temperature were the most important factors. Our observations indicated that the 15–16 h category of daylight presented the highest risk of development of cycle disorders with the most rapid increase observed for HAF. With respect to age, the highest occurrence of ovulatory failures was observed in the category of 15–24 years. The external temperature in the range of 18.1–23.0 °C affected the most the development of cycle disorders. Again, the effect was most evident with respect to HAF. This resulted in our recommendations for horse breeders that they should manage reproduction of their mares in a way so that the receptive phase of the cycle does not occur in the months during which the daylight length and environmental temperatures support ovulatory failure. We also recommend that if the owner′s wish is to keep in the breeding the mares older than 15 years, regular thorough gynaecological examination of these animals should be ensured, aimed at early diagnosis of ovulatory failure.