Location: Warmwater Aquaculture Research UnitTitle: Body Temperature Versus Microclimate Selection in Heat Stressed Dairy Cows Author
Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2005
Publication Date: 3/1/2005
Citation: Hillman, P.E., Lee, C.N., Willard, S.T. 2005. Body Temperature Versus Microclimate Selection in Heat Stressed Dairy Cows. Transactions of the ASABE. 48(2):795-801. Interpretive Summary: Heat Stress is a major problem in the southern region which can result in reduced production performance in dairy cattle. The purpose of this study was to characterize the thermoregulatory responses of unrestrained heat-stressed dairy cows within a freestall environment using fan and spray configurations for cooling cows while lying or standing. This study determined the critical temperatures at which point cows actively seek cooling. These data may be used to make engineering decisions regarding freestall configurations in hot climates, and to determine the types of cooling needed (fans vs. fans and sprinklers) to offset the adverse effects of heat stress on production performance.
Technical Abstract: The purpose of this study is to characterize the thermoregulatory responses of unrestrained heat-stressed dairy cows within a freestall environment using fan and spray configurations for cooling cows while lying or standing. An experimental treatment sprayed individual cows lying in freestalls from 11:00 to 15:00 (stall cooling period) during hot-humid weather (average THI of 82.4) over a five-day trial period, using ultrasound transceivers to detect their presence. Core body temperatures were continuously monitored with vaginal temperature loggers. To assess behavioral responses, cows were visually monitored during the stall cooling period. Respiration rates and dorsal surface temperatures were recorded when the cow lay down or stood up in a stall. Core body temperature of lying cows rises at a rate of 0.6°C h-1 when exposed to fan cooling alone. Adding spray cooling to fan cooling slows the rate of rise to 0.3°C h-1. With or without freestall spray cooling, cows stand and seek cooling when their core body temperatures reach 38.9°C. Core body temperature is a more reliable indicator than either dorsal skin temperatures or respiration rates for predicting when cows stand and seek cooling. Core body temperatures of cows fall at a rate of 0.7°C h-1 while standing under feed line spray and fan cooling, while core body temperatures of cows standing under fans without spray remain unchanged. To cool heat-stressed cows, water spray is required in addition to fans while the cows are standing. Fans alone are inadequate.