Estresse por calor em vacas leiteiras em ambiente tropical: efeitos na composição do leite e percepção dos produtores

Abstract

Firstly, the objective was to calculate the stress/control (S/C) ratio related to milk components from dairy cows in an important milk producing region of Minas Gerais, Brazil, which could serve as a practical application in other tropical regions. Daily maximum temperature and minimum relative humidity data were used to calculate the maximum daily Temperature and Humidity Index (THImax) in Araxá, Sacramento and Uberaba, Minas Gerais, Brazil, from 2017 to 2020. The three months of each year with the highest number of days with THImax ≥76 (S) and with the highest number of days with THImax <76 (C) were determined. A total of 10.063 analyzes for fat, protein, lactose, total solids and solids-not-fat of refrigerated raw milk from crossbred cows were determined in the same period and were used to calculate the averages of these components in periods S and C and the S/C ratio. The milk fat content was reduced during the heat period, with S/C values below 1.0 and most S/C ratios referring to protein, and total solids were also below 1.0. The S/C ratio values for lactose, but solids-not-fat differed little from 1.0. Therefore, A THImax greater than 76 causes changes in the milk composition of crossbred dairy cows in tropical regions, mainly with a reduction in fat contents, generating an S/C ratio less than 1. In the second research, the objective was to evaluate the knowledge and perception of dairy farmers about heat stress and what were the corrective measures that they managed to adopt to minimize losses in productive performance due to high temperatures. A questionnaire was applied to 112 dairy farmers in the states of Minas Gerais and Goiás, Brazil, from 2019 to 2020. Among the interviewees, 89% stated that they had already been informed about what heat stress is and how it affects animals, 94% declared that they had already noticed in their daily rotine that heat stress impairs productivity and quality of milk and 92% stated that they try to reduce the heat stress to which the animals are exposed. Thus, in important municipalities of the Brazilian dairy chain, most dairy farmers interviewed have knowledge and perception of the negative effects of heat stress on the productive performance of dairy cows and, therefore, seek to adopt measures that can alleviate them.