The objective of this study was to evaluate the effects of acclimatization of the milking ambient (ventilation and ventilation + water spraying) on milk production, milk composition (fat, protein, lactose) and plasma concentration of cortisol, T3 and T4. The experiment was conducted from August to October during 90 days. Twenty-one lactating dairy cows with milk yield around 21 kg d-1 were allocated three random treatments. The tested treatments were: 1) waiting room without climatization (CONTR); 2) waiting room with ventilation (V) and 3) waiting room with ventilation + water spraying (VA). Milk production data were collected daily and for milk composition, samples were collected once a week. Blood samples for hormone determination were collected weekly, from the coccigea vein. Data were analyzed by computer program SAS PROC ANOVA. Results showed no significant differences among treatments for milk production; the treatment ventilation had higher fat content; and the control group had higher concentrations of cortisol, T3 and T4 followed by treatments 2 and 3. The treatment VA although increased animal comfort it was insufficient to improve milk production, probably because of short time exposure (30 min).
heat stress; climatization; cortisol; tiroxina; triiodotironina; milk production
