KEEPING THE FANS ON!

Miner Institute has conducted several studies over the years evaluating the impact of heat stress on dairy cattle in Northern NY on farms with different types of heat abatement systems. This research was supported through funding from the Northern New York Agricultural Development Program. We used the smaXtec system to monitor body temperature from the reticulum at 10 minute intervals 24/7. This provided great insight into how body temperature changes during heat stress over the course of the day. What time of day do you think cow body temperature is the highest on a typical hot day in Northern New York?

Over the years, I have asked this question to audiences of dairy producers and generally get the answer of mid to late afternoon. Before indwelling temp loggers, most researchers of heat stress monitored body temperature in cows rectally at 10 am and 4 pm…thinking that 4 pm would capture the hottest time of day for cows since generally night cooling takes place in the evening and overnight. The figure below shows how cow body temperature fluctuates over the course of a 24 hour day when the average Temperature Humidity Index (THI) for the day is low (THI<68), moderate (THI 68-72) and high (THI>72) for lactating dairy cows. As you can see, body temperature was lowest around milking times at 4 am and 4 pm and were surprisingly the highest during the middle of the night. To save on the energy bill, I know some farmers who shut off the fans at night, thinking the cows will be cool enough as the temperature drops. One attendee at a meeting asked me to send her this figure because her mother-in-law is always shutting off the fans at night and now she could show her some data that supports keeping the fans on.

— Katie Ballard

ballard@whminer.com