Phenotypic plasticity and behavioral responses of girolando heifers on continuous grazing in the semiarid of pernambuco

The indicators of thermal stress for ruminants are described according to the magnitude of the meteorological elements, physiological, behavioral adjustments, and productive response. This research was conducted to evaluate the ingestive behavior and phenotypic plasticity of Girolando heifers subjected to continuous grazing in the semiarid of Pernambuco. Three heifers of 7/8 Dutch-Gir genetic composition were evaluated, submitted to a paddock with 40 x 40 m brachiaria, for 21 days. The meteorological variables recorded in the production environment were the dry bulb temperature (°C) and the relative humidity of the air (%), which allowed the thermal characterization through the temperature and humidity index (THI). The behavior of heifers was quantified through observation by instantaneous scanning of activities, walking, drinking, eating, ruminating, lying down, leisure and standing. The physiological responses recorded were rectal temperature (°C) and respiratory rate (movement min-1). The experimental design was completely randomized in a 2 × 3 factorial arrangement (shifts x evaluation period). Behavioral variables were subjected to the chi-square and probability test. The physiological parameters were subjected to analysis of variance and application of the Tukey test at the level of 5% significance. The THI did not exceed 89 units, which characterizes the critical limit of moderate stress for the animals. The heifers proved to be adapted to the climate of the region, as, during the study period, they showed sufficient physiological and behavioral alteration capacity to maintain homoeothermic.