Effects of ambient temperature and humidity on body temperature and activity of heifers, and a novel idea of heat stress monitoring

Abstract

Context Heat stress has led to a serious reduction in dairy cows production performance, thus increasing the stress of feeding and reproduction management. Aims Heat stress arises when cows are unable to dissipate excess body heat, we aimed to investigate the effects of ambient temperature (AT) and humidity on diurnal body temperature and activity. Methods For improving the technology for rearing dairy cows, the vaginal temperature (VT) and activity of 60 Holstein heifers in summer (n = 20), autumn (n = 20), and winter (n = 20) were measured using the oestrus monitoring system. Key results We found that VT fluctuated slightly (~38.22–38.32°C) when AT and temperature-humidity index (THI) were lower than 20°C and 68, respectively. However, when this threshold is reached, VT increased significantly with increasing AT and THI, whereas activity decreased significantly. Conclusions Heat stress may be caused when THI is above 68 and cow’s VT reaches 38.32°C. Evidently, when the THI exceeds 68 and VT is more than 38.32°C, suitable measures for reducing the effect of heat stress on the productivity of dairy cows should be taken. Implications The combined monitoring of VT and THI might provide accurate guidance for preventing and controlling heat stress.