Efeitos da composição genética e de fatores ambientais na temperatura vaginal em novilhas leiteiras Girolando

Abstract

Even with the advances in the selection and crossbreeding of high milk-producing cattle breeds, such as Holstein and Gir, high temperatures in subtropical and tropical climates can impact milk production and reproduction, presenting challenges. The Girolando breed has different genetic compositions, and it is assumed that this results in different responses to heat stress, with a higher proportion of Holstein genetic origin. Thus, the main objective of this study was to evaluate the effect of genetic composition on the vaginal temperature (VT) of dairy heifers with 1/2, 3/4, and 5/8 Holstein x Gir genetic compositions during the hot season in October 2023, on a commercial farm located in the city of Morrinhos - GO, which has a tropical climate, in addition to environmental factors related to temperature and air humidity and the age of the heifer. “iButton” devices with intravaginal insertion were used to obtain VT measurements. Meteorological data were obtained from the National Institute of Meteorology (INMET) for the calculation of the temperature and humidity index (THI). A mixed model with repeated measures was used in the VT analysis. Pearson correlation (r) was used to estimate the phenotypic correlations between VT and THI by genetic composition. The magnitude of the Pearson correlation of the vaginal temperature (VT) variable with the THI environmental variable was positive and weak for 1/2H, positive and moderate for 3/4H, and positive and moderate for 5/8H, with significant p-values (p<0.05). Among the effects of the model that were significant (p<0.001), genetic composition stands out. The mean VT values were 38.4±0.25 °C, 38.6±0.39 °C, and 38.4±0.31 °C for 1/2H, 3/4H, and 5/8H, respectively. The model results suggest that the average VT of the heifers is affected by the proportion of Holstein genetic contribution. In conclusion, 1/2H and 5/8H heifers had better thermoregulatory capacity during the study period compared to heifers with a 3/4H genetic composition.