Thermoregulatory Responses Associated With Lying and Standing in Heat-Stressed Dairy Cows

The purpose of this study is to characterize the thermoregulatory responses of unrestrained heat-stressed dairycows within a freestall environment using fan and spray configurations for cooling cows while lying or standing. Anexperimental treatment sprayed individual cows lying in freestalls from 11:00 to 15:00 (stall cooling period) during hot-humidweather (average THI of 82.4) over a five-day trial period, using ultrasound transceivers to detect their presence. Core bodytemperatures were continuously monitored with vaginal temperature loggers. To assess behavioral responses, cows werevisually monitored during the stall cooling period. Respiration rates and dorsal surface temperatures were recorded whenthe cow lay down or stood up in a stall. Core body temperature of lying cows rises at a rate of 0.6C h-1 when exposed tofan cooling alone. Adding spray cooling to fan cooling slows the rate of rise to 0.3C h-1. With or without freestall spraycooling, cows stand and seek cooling when their core body temperatures reach 38.9C. Core body temperature is a morereliable 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 0.7C h-1 while standing under feed line spray and fan cooling, while corebody temperatures of cows standing under fans without spray remain unchanged. To cool heat-stressed cows, water spray isrequired in addition to fans while the cows are standing. Fans alone are inadequate.