Diurnal Changes in Thermoregulatory Responses of Lactating Dairy Cows during Summer and Autumn

Abstract

Diurnal thermoregulatory responses of eight Holstein cows, such as heat production (HP), heart rate (HR), rectal temperature (RT), skin surface temperature (ST) and respiration rate (RR) were observed on four days during summer and autumn at the northern part of Hiroshima prefecture. The average milk production was 29kg/day at the beginning of this study, and the cows were fed with a concentrate mixture and corn silage at 0600 and 1800, according to Japanese Feeding Standard. HP during the night (2100-2200) was higher than that in the morning (1000-1100) and afternoon (1500-1700). A low level of HR was observed in the early morning and it then gradually increased until late at night. RT reached a minimum level between 0800 and 1000 and then gradually increased to maximum level between 1600 and midnight. ST of the abdomen decreased during and after feeding and then increaed until midnight. Levels of RR were influenced by ambient temperature, and RR decreaed during and after each feeding and increased during daytime and early night. The large intake of water during each feeding prevented increasing responses in RT, ST and RR, but had no effect on HR and HP. The most useful physiological response which indicate the diurnal change of thermal state in dairy cow is the RT. It is suggested that the effective measurement times of RT are in the morning, evening and midnight, when the minimum, maximum and maintained maximum levels or state of declining RT could be observed.