Estresse térmico em bovinos leiteiros

Abstract

During years researchers from many countries studied heat stress. However even nowadays farmers face a big challenge to maintain milk yield in the hottest days of the year. Respiratory rate (RR) and rectal temperature (RT) are used as indicators of heat stress. Moderate stress is characterized when RR and TR are above 70 bpm and 39,2°C, respectively. The ambient temperature associated with air humidity is combined into an indicator of thermal comfort, which is named temperature and humidity index (THI). The ideal THI able to prevent any physiological or behavioral changes and production losses in dairy cattle must be less than 68. The yield loss may reach about 35% and most of the reduction in production can be explained by the smaller amount of dry matter intake and increased energy usage for regulation of homeostasis. Also there is a significant reduction in reproductive efficiency of cows due to silent estrus and reduction in time and intensity of estrus. The purpose of this literature review is to analyze the negative effects of heat stress in dairy cattle and discuss management strategies to lessen their influence and increase the profitability of production.