Influence of meteorological elements on behavioral responses of gir cows and effects on milk quality

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.摘要。本研究旨在分析不同挤前冷却时长处理下奶牛的气象变量、生理与行为响应的主成分，及其在旱季与雨季对牛奶品质的影响，并建立牛奶品质的多元回归预测模型。本研究所用数据源自巴西伯南布哥州阿格雷斯特地区开展的一项试验。实验设置挤前冷却时长分别为10、20、30分钟，另设不进行冷却的对照组。共选取16头经产泌乳吉尔奶牛（Gir cows）作为试验对象。研究采用主成分分析法对采集数据进行分析，并通过多元回归分析构建牛奶品质预测模型。结果表明：旱季时，奶牛在遮阴区域的活动量与乳中体细胞数（Somatic Cell Count）存在显著强相关关系；雨季时则为躺卧时长与体细胞数相关，且上述行为指标升高均会导致奶牛乳体细胞数增加。本研究成功构建了适用于旱季与雨季的两套牛奶品质多元回归预测模型。基于主成分分析结果，无论所处季节与挤奶班次如何，满足奶牛热舒适需求的挤前冷却时长为20分钟。