The aim of this study was (i) to evaluate the relationship of climatic factors with gestational length (GL) and (ii) to evaluate the relationship of sire, foal gender and maternal factors with GL in mares. Retrospective data from 470 gestations of 202 respective mares were collected from a Criollo breeding farm in the southern hemisphere. GL was considered as the interval between ovulation and parturition. Climatic and environmental data (temperature, relative humidity, daily sunshine hours, precipitation, temperature humidity index - THI) were obtained daily and the mean values for foaling month and season were calculated. A multiple factor analysis of variance was performed to determine the relationship of the independent variables and interactions related to the mare, foal gender and stallion, and those related to the weather in each season of the year with GL as the dependent variable. The mean ± standard error (SE) of GL for the 470 gestations was 337 ± 0.4 days with a range of 311-363 days. Young-primiparous mares (340±0.9) had longer gestations (P < .001) than young-multiparous (336 ± 0.7) and mature-multiparous (334 ± 0.7) mares. Foal gender had no effect on GL. Gestational length was found to be affected by the stallion. Mares which experienced an autumn and winter gestational period with less daily sunshine hours had an increased GL (P < .05). In conclusion, environmental and climatic factors during pregnancy influenced the GL in mares, specifically, daily sunshine hours, precipitation and THI presented a negative correlation with GL. Young-primiparous Criollo mares presented longer gestational lengths than young or mature multiparous mares.
Keywords: Daily sunshine hours; Equine; Parity; Stallion; Temperature-humidity index-THI.
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