By Rick Lundquist, Ph.D.
Now that we’re in the heat stress season, it’s important to do everything possible to keep your cows cool. I’ve discussed summer ration adjustments in this column before. Providing an ample source of clean, easily accessible water is the most important nutritional consideration. But heat abatement with shade, fans and sprinklers is critical to avoid heavy milk losses in the summer.
Body temperatures greater than 102.2° F can have a detrimental effect on the developing embryo from day one through six and may result in early pregnancy loss. So, we can consider body temperatures above this as indicative of a heat-stressed cow.
It’s relatively easy to determine if the body temperature of your cows is in the heat-stress zone. You don’t have to temp cows or use a recording device. Respiration rates are highly correlated to body temperature. Count respiration rate by watching the flanks move or the nostrils. If cows are breathing with an open mouth, observe the movement of the cheeks. Check at least eight to 10 cows in a pen by counting for 20 seconds and multiplying by three to get respirations/minute.
Check a few cows before and after they go to the holding pen to see if the respiration rate has increased. Heat stress usually peaks in mid to late afternoon. However, don’t overlook the importance of cooling cows in the late evening and early morning since this is the time when humidity levels drastically rise, creating high heat indexes. Cows have difficulty dissipating heat at this time due to a “sauna” effect.
The following graph, which was published in the 2002 Arizona Dairy Producer Conference Proceedings, shows the relationship between respiration rate and body temperature. Use this graph to determine the body temperature of your cows from their respiration rates. Normal body temperature is 101.5° F and normal respiration is about 45 breaths per minute. Cows are most comfortable at temperatures between 40° F and 60° F.
Elanco Dairy Business, with the collaboration of many experts on heat stress, has published an excellent heat abatement guide that can help you minimize the effects of heat stress in your herd. This guide gives specific recommendations on shades, fans and sprinkler systems.
Contact your Elanco representative if you'd like a copy of the heat abatement guide, It's not available online.
Rick Lundquist is an independent nutrition and management consultant based in Duluth, Minn. Contact him at firstname.lastname@example.org.