Why you can’t allow a cow’s body temperature to rise above the critical point at any time of the day or night.
By Rick Lundquist, Ph.D.
My clients have come a long way with heat abatement in recent years. It’s paid dividends in sustained milk production during the summer. I think I can safely say that my Florida clients deal with heat and humidity that will rival anywhere in the world. But we can always do better. Summer milk production has fared better than summer reproduction. We still see summer pregnancy rates in the single digits on some dairies.
Nutritional strategies help combat heat stress (more frequent feedings, high quality forage, higher DCAD, etc). But the best way to reduce the effects of heat stress is to reduce the heat.
I asked Dr. Jose Santos of the University of Florida to visit a few of my clients south of the I-4 corridor last month to address our reproduction and heat abatement issues. South of I-4, which runs between Tampa and Orlando, is where the tropics begin in Florida. Reproduction suffers here in the summer. One comment by Dr. Santos stuck in my mind; at an internal body temperature of 103 degrees F, we are frying embryos. That means when I see a cow with a respiration rate of 80 or more that has recently become pregnant, chances are that embryo is dead.
I visited a dairy in Florida last week that had probably the best heat abatement I’ve seen. There were sprinklers over the feed lanes, fans (all working) over the feed lanes and beds, fans over the holding areas with sprinklers over and under the cows, soakers in the exit lane and rainbirds in the travel lanes. This is how a comprehensive heat abatement system should look in hot, humid climates.
We can’t allow the cow’s body temperature to rise above the critical point at any time of the day or night, or much of our heat abatement could be wasted. Holding pens are critical because body temperature can spike here when cows are crowded.
How long does it take for the internal temperature of a cow to return to normal after she gets hot? That’s a lot of mass to cool down. Research shows that once a cow gets hot (103 F body temperature or more) it takes at least 45 minutes to cool her down if she is under fans and soakers. Damage to the embryo may already be done. Otherwise, it can take 6-8 hours for her body temperature to return to normal at an ambient temperature of 68 degrees.
Hat’s off to Dr. Tom Bailey and the team from Elanco for putting together a comprehensive heat abatement guide. Following the recommendations in this guide will definitely reduce the effects of hot weather on our herds.