Phenotypic Plasticity and Behavioral Responses of Dairy Cattle on Rotational Grazing.

Heat stress is one of the most important environmental challenges faced by dairy cattle, with a deleterious effect on animal production and welfare. This research was conducted to evaluate the effects of the thermal environment on the physiological and behavioral responses of dairy cattle in a rotational picket. The research was conducted on an experimental farm, located in the Agreste region of the state of Pernambuco, Brazil. The animals were managed in a rotational picket system of signal grass, with an occupation and a rest period of 7 and 28 days, respectively, for a stocking rate of 3.2 AU ha−1. The determination of the effect of stressors on the animals was performed by recording the dry bulb temperature (°C), and the relative humidity, which allowed the characterization of the thermal environment by the temperature and humidity index and by the specific enthalpy (kJ kg−1). The physiological variables monitored were respiratory rate (mov. min−1), rectal temperature (°C), and skin temperature (°C). The behavioral responses quantified were activities, walking, ruminating, idling and ingestive behaviors, eating, and drinking, with the percentage of time spent on each activity being recorded. According to the canonical multivariate analysis, the chi-square test, and the variation of physiological patterns, the animals, even in a situation of greater thermal challenge, presented physiological responses within conditions considered normal; however, they reduced grazing activity (eating) during the hottest hours and increased the activities of rumination and idling.