Índices de conforto térmico, variáveis fisiológicas e desempenho produtivo de vacas leiteiras em sala de espera climatizada

Abstract

With genetic improvement of animals in recent years, heat stress being a main factor limiting milk production in the tropics. Climate strategies have been used to mitigate these effects, such as shading, sprinkling and the SRAE (Adiabatic Evaporative Cooling System). The aim of this study was to evaluate different environments in the holding pen, through the physiological responses of animals, thermal comfort indices, milk production and economic gains. The research was conducted in a dairy farm located in Trindade-GO, during the October and December (spring). Sixteen lactating dairy cows were chosen, they were randomly divided in four groups. Latin square design was used, four groups in four periods, testing four environments: SOL - external environment, exposed directly at sun (control); SOM – ambient with shadow of polypropylene with 80% sunshine interception; SOM+ASP - shading with polypropylene (80%) and sprinkling; SOM+ASP+VEN - shading with polypropylene (80%), sprinkling and ventilation. The cooling was made in the milking of afternoon, during 30 minutes. During the cooling was collected ambientals variables, dry bulb temperature (Tbs) Relative humidity (UR), black globe temperature (Tgn), wind speed (m s-1), through of data loggers every minute. After this, the indexes were calculated: Temperature Humidity Index (THI), Black Globe Temperature and Humidity Index (BGHI), Radiant Thermal Load (CTR), Heat Load Index (HLI), and Enthalpy (H) After climatization was collected physiological variables: respiratory rate (RR), surface temperatures at the five points (head, back, shin, udder, rump) and rectal temperature (RT). has been made correlation analysis between environmental and physiological variables. The treatment SOM+ASP and SOM+APS+VEN showed significant improvements (P<0.05) in environmental variables and comfort thermal index, reflecting positively on production rates. The index that most correlated with the physiological variables was BGHI. The treatment SOM+ASP+VEN was an increase of 9.31% and 6.5% compared with the SOL and SOM environments, respectively. The cooling of SOM+ASP+VEN increased R$ 3.364,02 in financial income, with the return on capital-invested time of 44 days.