A combination of events provided motivation for the writing of this post. I received a number of requests for information regarding dealing with heat stress over the past seven days from fellow cattlemen and blog followers. In addition, I spent the latter part of the week and the weekend trying to effectively care for newly received fall calves experiencing severe heat stress due to grazing toxic fescue grass prior to shipment off of the ranch to my feed yard.
The threat of heat stress to animals is very real and, while it cannot be truly abated by anything other than a reprieve from Mother Nature, there are things that we can do as animal caregivers to help our cattle to more effectively deal with it. Below is a list of facts that every cattlemen should know about cattle and their tolerance to heat. The information comes from Dr. Dee Griffin and Dr. Terry Madar.
- 55 degrees is “short sleeve” weather for cattle — 82 degrees is upper critical temperature.
- It takes a calf 30 days to acclimate to warm temperatures (approximately 1 degree per day).
- Heifers are more susceptible to heat than steers due to natural female cycling.
- Air flow and wind are critical as they decrease the heat index temperatures according to wind speed ( 1 degree = 1 MPH drop in index temperature).
- Humidity exacerbates heat stress: cattle are much more comfortable in dry heat.
- Black hided cattle are more susceptible to heat stress than lighter colored animals as their internal temperature will be 1-1.5 degrees higher.
- High performing animals often have a faster metabolism and as a result can be affected the most by heat.
- Stable flies (and other flies and gnats) increase total stress on animals so it is important to maintain the farm to limit insect pests.
- Water requirements of cattle increase from 10% to 20% per hundred weight of body weight during times of heat stress. An ample source of cool and clean water provides your best mitigator against heat stress.
- Hot days combined with nights where the temperature does not fall below 70 degrees are the most problematic, especially if humidity is significant and wind speed is low.
- There is a two hour lag between the highest heat of the day and when a calf has the highest level of heat stress — after the peak, it takes approximately 6 hours for the calf to cool down.
Below are a list of practices that I employ on my farm to help my animals get through the heat of the summer:
- I manage the business part of the feed yard such that the majority of our larger animals ship to harvest prior to the high onset of heat in July and early August.
- I reduce the total number of head of cattle in each pen so that there is more room for air flow across the pen as well as more access to the cool water that the water tank provides for drinking.
- I maintain my pens such that tall mounds allow for cattle to better take advantage of wind speed.
- I move in portable shades to the pens of cattle closest to harvest dates, as well as cattle that are more susceptible to heat stress as a result of another challenge (like toxicity from fescue grass on the ranch prior to shipment to the feed yard).
- Any cattle handling (acclimating, processing or shipping) occurs during the early morning hours during cooler temperatures.
- Breakfast is delivered early (between 6-8:00am) so that all cattle can eat prior to the onset of heat. We feed “linner” (my girls’ expression for the combination of lunch and dinner) later in the afternoon so that cattle can eat again at night.
- Our daily cattle health check is performed early in the morning prior to the onset of heat so that if an animal requires individual attention, it can be provided during the cooler hours of the day.
- I feed MGA to heifers in the feed yard to prevent the natural female cycling that raises her internal body temperature.
- My crew and I take special care to not “over feed” our animals during times of heat stress. Careful feed bunk management is critical to animal health and comfort — especially in the hot summer months.
As mentioned above, ample cool drinking water (in Nebraska our water comes out of the Ogallala Aquifer in the summer at a temperature of 58 degrees which gives our animals a nice cool drink) and access to air flow (wind) are the two most critical components for alleviating severe heat stress.
It takes a “team effort” to help our cattle, and I am proud of my crew’s dedication to caring. I am also thankful to have a team of dedicated veterinarians and nutritionists to help us make the best decisions for our animals.