Parâmetros fisiológicos de vacas F1 Holandês x Zebu em fase de lactação, em ambientes com e sem sombreamento durante o verão

Abstract

This study aimed to characterize the climate effect provided by two distinct environments on the physiological responses of F1 HxZ cows lactating during the summer. The experiment was conducted at the Agricultural Research Company of Minas Gerais (EPAMIG) during summer 2015. We evaluated 34 lactating cows, 4 different genetic groups F1 HxZ. During the trial period, daily measurements of variables were made environmental: dry bulb temperature, relative humidity and black globe temperature, beginning with the 7 am and 4 pm and then calculated the IBGT values. The physiological parameters respiratory rate (RR), heart rate (BC), body surface temperature (TSC), rectal temperature (RT), and sweating rate (SR) were obtained at 7 am and 2 pm. The weighing of the milk to determine the average production of animals was done weekly. The experiment was conducted using a completely randomized design (CRD) in a factorial 4 x 2 x 2, four genetic groups, two rooms and two times with 34 repetitions. In preliminary analyzes, the four genetic groups studied were similar, and therefore were unified. the correlation among physiological parameters and environmental variables and regression analysis was performed. The variables were subjected to analysis of variance using the statistical package SAS (Statistical Analysis System), and when the F test was significant, had the treatment means compared by Tukey test (P <0.05). F1 animals raised on pasture without shading and natural shade, do not suffer from changes in physiological patterns indicative of stress and do not reduce milk production. The globe temperature and humidity level reached values considered stressors, but the creation environments did not produce stress and reduction in the production of animals. This suggests that more research about the critical values of these indices, which would allow the identification of values to reflect more accurately the thermal stress of the F1 animal.