Behaviour, tympanic temperature and performance of dairy cows during summer season in southern Chile

Abstract

The objective of the study was to assess the effects of summer weather conditions on animal performance and behaviour in southern Chile. Data of milk yield, animal activity, tympanic temperatures (TT; n = 15), and three comfort thermal indices were collected in La Araucania Disctrict. Time of day and comprehensive climate index (CCI) categories were considering as influential factors. Simple regression models were estimated to predict the respiration rate of cows as an estimator of thermal comfort. Daily values of thermal indices were poor predictors of respiration rate, as well as climatic variables (r² < 0.35; P < 0.001). During days with CCI ≥ 25 there was a reduction (P < 0.002) in the proportion of animals on grazing (9.4%), lying (1.7%), and ruminating (5.4%). The proportion of animals standing and under shade increased 7.4 and 6.3%, respectively. Respiration rates were positively correlated with greater CCI values. The TT was higher for CCI categories "moderate" and "mild" vs. "normal" also for PM vs. AM. The highest TT was observed on days that had higher values of the thermal indices, especially CCI. There were differences for milk production and CCI values between AM vs. PM (P < 0.001). However, no differences for milk production were observed between CCI categories observed (P = 0.19). In conclusion, although cows showed signs of heat stress daily milk production did not show differences among CCI categories, showing that they were able to cope adverse climatic conditions of summer in southern Chile.