Tempo de gestação de éguas puro sangue inglês mantidas em clima tropical e subtropical

Abstract

The gestation length (GL) in horses varies widely, with the interval between 320 and 360 days being considered physiological. It is known that gestation time can be influenced by several maternal, fetal and environmental factors, however, information about the effects of climatic factors is limited. In the Thoroughbred breed it has an average of 344 days, however, in the literature it is not described which climatic effects would affect this period. This dissertation in the first article presents a review about the factors influencing gestation length in mares. The second article aims to compare Thoroughbred mares' gestation times, relating GL with climatic factors: temperature humidity index (THI) and photoperiod in the month of delivery, in addition to relating GL with maternal factors (age and number of births), fetal factor (gender of the foal), environmental factors (year and month of birth) and the stallion. The mean TG of the 704 pregnancies studied was 342.6±10 days. Stepwise regression was performed and the independent qualitative variables that showed significance in the regression analyzes were submitted to One-Way Analysis of Variance and comparison between means by the Tukey test. It was observed that pregnancies in male foals (343±10.58) were on average two days longer than pregnancies in female foals (341±10.15) (p=0.002). From the multiple regression analysis and evaluation of the standardization coefficient, the independent variables were ranked in decreasing order: month of birth, year of birth, foal's gender, age of the mare, THI and number of births, which can be described according to the following formula: y = 311.893 + 3.086monthbirth +1.113yearbirth+ 2.149Gender+ 0.714Age -0.160THI -0.632N° of births (r2 = 23.6). According to the results, the study demonstrates that Thoroughbred mares that remained under higher THI values in the month of parturition have shorter gestation times, demonstrating a negative relationship between these climatic factors and the gestation time in Thoroughbred mares.