Influence of Different Heat-Stress-Reducing Systems on Physiological and Behavioral Responses and Social Dominance of Holstein and Jersey Cows and Heifers on Pasture

SIMPLE SUMMARY: A suitable environment for dairy cows has become increasingly important, especially in the summer in tropical countries. Excess heat increases body, hormonal, reproductive responses, and behavioral temperature, and may in extreme cases lead to death. This research shows the importance of using systems that can reduce the heat stress of dairy cattle raised on pasture. In this study, climatic parameters of the thermal state of the environment during the period, and the physiological, behavioral, and preferential responses of Holstein and Jersey cows and heifers on pasture were evaluated. The results showed that dairy cows preferred to use sprinklers or showers over artificial shade under ambient conditions, especially lactating and Holstein cows versus pubertal heifers because they are more thermosensitive. These systems are more efficient in dissipating heat by evaporation, improving the welfare of the animals, especially those raised on pasture. ABSTRACT: High ambient temperatures and relative humidity affect the behavior and physiology of the animal. This study investigated the influence of different heat-stress-reducing systems on the physiological, behavioral, and preferential responses of Holstein and Jersey cows and heifers on pasture. Experimental treatments were: (1) three heat-stress-reducing systems (sprinklers + artificial shade; showers + artificial shade; and artificial shade); (2) two breeds (Holstein and Jersey); and (3) two physiological stages (lactating cows and pubertal heifers). Physiological and behavioral responses to treatments were measured every 30 min on collection days. The frequency and duration of the use of the systems were recorded continuously 24 h/day for 3 days in each period. The air temperature and the relative humidity were 26 ± 4.1 °C and 74 ± 11.3%, respectively. The experimental treatments affected (p = 0.0354) standing idle, grazing behavior (p = 0.0435), and the frequency and duration of use of the systems by the animals (p < 0.0001). For all treatments, the respiratory rate and the coat surface temperature were highly and significantly correlated (p < 0.05) with the temperature and humidity index. In conclusion, under ambient conditions, dairy cows preferred using sprinklers or showers over artificial shade. These systems were more efficient at reducing the heat load and led to better behavioral and physiological responses.