Predicción de estrés térmico en vacas lecheras mediante indicadores ambientales y fisiológicos

Dairy cows have become very sensitive animals to environmental changes, requiring increasingly sophisticated accommodations to prevent the stress that would lead to major production and economic losses. The aim of this study was to assess environmental and physiological indicators of stress in cows and their influence on milk production. The temperature and relative humidity was monitored at intervals of one hour through digital probes placed in four farms for 365 days. Alongside two animal physiological indicators (rectal temperature and respiratory rate) were collected, in winter and summer. The results showed the presence of 48 days in a year with temperatures above 25 °C, with the most critical periods occurring in spring and summer. The relative humidity ranged from just 10 % between winter and summer. The Temperature Humidity Index (THI) exceeded the value of 72 on 51 days per year. The most critical period of the day recorded was between 12:00 to 16:00 p.m. (P4) where the average of THI was 68.0. From THI value below 72 to above 78, a rise of 1.3 °C and 37.3 breaths/minute was observed in the monitored dairy cows. We found a high correlation between respiratory rate and rectal temperature and of both with the THI, highlighting these physiological indicators as excellent predictors of heat stress. The animals exposed to higher THI than 78 showed a loss in milk production of 1.8 kg/cow/day.