Abstract
This study aimed to analyze the principal components of the meteorological variables, physiological and behavioral response of cows subjected to different cooling times and their influence on milk quality, in the dry and rainfall periods, and to establish multiple regression models for milk quality. The data used in the study came from an experiment conducted in the Agreste Region of Pernambuco. The pre-milking cooling time was 10, 20, 30 min. and the control (without cooling). Sixteen multiparous lactating Gir cows were selected. Data were analyzed by principal component analysis and a multiple regression analysis was applied to determine milk quality. There was a strong relationship between somatic cell count (SCC) and activity of the animal in the shade for dry, and lying for rainfall, with increased SCC in cow milk. It was possible to establish two multiple regression models to determine milk quality in dry and rainfall periods. According to the principal component analysis, the cooling time to meet the thermal requirement of the animals was 20 min., regardless of the season and milking shift.
Highlights
The principal component of each variable in the dry showed somatic cell count (SCC) strongly influenced by air temperature (T), rectal temperature (RT), activity of the animal standing in the shade
The variables relative humidity (RH), wind speed (Ws), activity in the sun, rumination, walking, lying down, eating and drinking were inversely proportional to SCC
The application of the Principal Component Analysis (PCA) on environmental variables, behavioral parameters and milk quality of lactating cows was efficient to identify their effects on somatic cell count
Summary
Animal stress due to high temperatures affects both milk production and quality. This phenomenon often occurs in tropical, subtropical and temperate regions (Kadzere, Murphy, Silanikove, & Maltz, 2002; West, 2003; Liu et al, 2017). Improvements in the thermal conditioning of cows, seeking the best possible comfort for these animals has been commonly investigated. Waiting pens or pre-milking rooms are critical points in the production units, because in these environments the animals are exposed to possible heat stress events that fluctuate in intensity and duration due to the adopted management
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