6/13/2011
Have a plan for heat stress
Summer is fast approaching, bringing with it the promise of hot weather and added stress for dairy cows. The symptoms of heat stress are easy to recognize. Rapid, shallow breathing with respiration rates of at least 60 breaths per minute, open mouth panting, extended tongues, and drooling are all indicators of animals experiencing heat stress. Less apparent are the effects this has on the cow internally.
A dairy cow undergoing heat stress is in survival mode. Her feed intake can decrease by 35%. Instead of mobilizing fat (which generates more heat), her body chooses to degrade protein. Protein degradation produces urea as a byproduct. Some of this urea can accumulate in the uterus resulting in reduced fertility and the remainder must be removed by the kidneys—a process that requires her to use more energy.
On the reproductive side, not only can fertility be reduced by the increased urea, but embryo survival is compromised at body temperatures exceeding 102.2°F, particularly in the first week after insemination. In the end she is not able to meet the energy demands required for maintenance and production; production is sacrificed and embryo survival is greatly reduced. Is it any wonder that production losses of 20 to 30 percent and single-digit pregnancy rates are common during the summer months?
The good news is you can mitigate some of these losses through cow cooling. Providing shade should be priority number one. Solar radiation can raise the temperature humidity index (THI) by 6 to 9°F. Also, make sure adequate drinking water is available.
Provide 3 to 4” per cow of linear tank perimeter. Keep in mind cows will consume 30 percent of their water upon exiting the parlor; make sure adequate space is available for all cows to drink upon exiting the parlor. Sprinklers and fans are also critical for effectively cooling cows. Research from University of Arizona shows that fans alone are not effective at cooling an already hot cow. This is not to say that fans are not beneficial. Fans can still increase airflow and delay the rise in temperatures in a barn. However, if you really want to cool cows and have a major impact on heat stress, water is critical.
Sprinklers and fans in the holding pen are a great place to start. The holding pen is the most stressful location on the farm and can be one of the best locations to add sprinklers. However, if sprinklers are added make sure to include fans or you can create a “sauna” effect with water alone.
Sprinklers over the feedbunk are the next priority.
Fans over the freestalls and the feedbunk should be next. All fans should be spaced so that at least 5mph wind speeds can be measured underneath the next fan. New recommendations are to turn fans on at 65°F and sprinklers at 68°F. Also, keep in mind fans need to be cleaned. Dirty fans can reduce fan efficiency by 40 percent.
For more information on recommended cooling systems contact your local Dairy Extension Agent.
Source: Beverly Cox, Extension Agent, Franklin County, Virginia Cooperative Extension
