Effects of Environmental Temperature and Air Movement on Thermoregulatory Responses of Lactating Cows

An Assessment of Air Movement in Terms of Effective Temperature

Abstract

Using the environmental controlled laboratory of the National Institute of Animal Industry weighting ratios of environmental temprature and air movement on thermoregulatory physiological responses of four lactating Holstein cows were investigated, and effectiveness of air movement was estimated in terms of effective temperature. Physiological responses, including rectal temperature, mean skin surface temperature from eleven different parts of the body, respiration rate and heart rate were measured at six levels of ambient temperature, ranging from 4°C to 30°C and five levels of air movement from no-forced blow to 2.25 m/s around the cow's head. Respiration rate and mean skin temperature increased with environmental temperature but decreased with air movement. No significant effect of either enviromental temperature or air movement on rectal temperature was found. Heart rate reached a minimal level at 8°C and increased as the temperature changed from 8°C to the other levels. With increasing of air movement heart rate tended to decrease. Weighting ratio of environmental temperature (DBT, °C) and air movement (√AM, m/s) on respiration rate and on mean skin temperatures altered as the zone of temperature ranged from cold to warm; the average weighting ratios were from 1:-9.2 to 1:-10.5. Effective temperature (ET), in terms of dry bulb temperature (DBT, °C) and air movement (√AM, m/s) could be expressed as follows. ET (DBT, AM)=DBT-10√AM. The usefulness of this formula is discussed in connection with the protecton of dairy cows from cold and heat.