Managing Heat Stress in the Feedyard

Randy Rosenboom, Field Specialist

I’m sure most of us remember the extended period of hot weather we had in the summer of 2011. While our market area south of Interstate 80 deals with heat quite frequently, those of us in the northern market area are not used to long-term periods of heat. However, heat is not the only factor to worry about, since humidity and lack of air movement make heat stress more severe. The “heat index” is a better indicator of stress than the simple reading on the thermometer.

Cattle on high-energy diets are the most susceptible to heat stress. This is not only because these diets generate more internal heat, but these cattle will be carrying more body condition which makes it more difficult for them to dissipate heat. Body temperatures peak due to feed intake 4-6 hours after ingestion. Unfortunately, this usually corresponds to the peak temperature during the day. The other factor that comes into play is that when cattle cannot dissipate heat, it tends to build internally much in the way a brick wall holds heat. You can place your hand on a brick wall that has been in direct sunlight hours after peak heat and it is much warmer than the ambient temperature.

Several strategies can help cattle cope with these physiological facts. Feeding 30% of the feed early in the morning and 70% in the early evening after peak heat will help minimize the affect of digestive heat. There is also a school of thought that supports reducing the energy density of the diet by 5-7%. This is approximately a 3 mcal drop in NEgain. While roughage fermentation does generate more “internal” heat, the overall heat generated by finishing diets, is still higher than it is on grower diets.

Providing “cooling zones” with sprinklers is a sound practice for heat management. Remember, cattle are cooled by evaporative cooling, not by being wet. Consistent availability of sprinkling water is more effective than waiting until the cattle are already hot and then soaking them with a fire hose. Start the sprinklers late morning, before it is hot, so the cattle can manage their own temperature. If you wait until tongues are hanging out, it is too late. Using a smaller particle sprinkler mounted high will help avoid the mud holes that aggravate producers, making them hesitant to sprinkle their cattle. None of my customers who used this strategy during last summer’s heat spell lost any cattle.

I also had feedback last summer that cattle being fed BoVantage +Optaflexx stayed on feed better and handled heat stress better than lighter cattle not on BoVantage +Optaflexx. This is contrary to expectations based on ration content and body condition. Since Optaflexx would not elicit this response, it makes sense that BoVantage was a factor. Observations by Dr. Michael Edmonds in a NutriVantage broiler trial support this idea. When periods of heat stress are inevitable this summer, encourage your producers to try straight BoVantage to see if it maintains feed intake and helps cattle better deal with the heat.