Aiming to evaluate the lactation performance and adaptability of confined dairy cows fed diets containing soybean and its by-products, this study used 12 Holstein cows with initial production of 30 kg milk-1 day-1 in feedlot system distributed in a 4 x 4 Latin square design. The experimental period lasted 84 days. The dry matter intake (DMI) and meteorological variables were recorded daily. Milk production was measured from the 15th to the 21st day, with milk analysis twice in each period, and physiological variables collected on the 15, 17th and 21st days of each experimental period. The thermal comfort indices and rectal temperature were considered normal, however the respiratory frequency and heart rate were different between the periods. Total milk production and percentage of crude protein were not affected. The thermal environment had influence on the CMS and on the percentage of milk fat in warmer periods, but the mechanism of heat dissipation was efficient for the animals to maintain homeothermy without affecting milk production.
production and composition of milk; rectal temperature; heat stress; thermoregulation
