Impact of environmental effects on milk production and clinical parameters in the Holstein breed

Abstract

Brazil is a country with a strong influence on dairy production and livestock. It presents a tropical climate with high temperatures in some periods of the year; therefore, it is considered necessary to know possible physiological changes and how much the temperature can affect its productivity. The present work aims to evaluate the effects of heat stress on the physiological parameters and milk yield of lactating Holstein cows. The experiment was conducted at the IF Sudeste MG zootechnic nucleus - Barbacena campus, using 16 lactating Holstein cows in a completely randomized design, divided into two treatments, T1 (thermal stress) and T2 (shading). Heart rate, rectal temperature and milk yield were not affected (P > 0.05) by the treatments. Heart rate averaged between 61 and 64 movements per mi-nute, while rectal temperature was within the range of 38° C, both variables showed no results. The respiratory rate parameter was affected (P < 0.05) ranging between 45 and 53 movements per minute, differentiating between the two times (morning and afternoon). Milk production averaged 8 liters, with no significant values in response to treatments. It was concluded that the heat stress on animals presented variation only for the respiratory rate parameter, and no result was noticed in the other parameters. Thermal stress can cause important changes in the physiological system of animals directly exposed to it, and the adoption of mechanisms that reduce these changes is extremely important.