The time to begin thinking about heat stress in our herds was months ago. While you can implement some mitigation techniques immediately, your blueprint for managing heat stress should be formulated now for the future.
Heat stress has been estimated to cost the beef industry millions of dollars annually. It arises when the animal cannot dissipate enough heat to maintain a normal body temperature, a process called “thermoregulation.” This frequently occurs in cattle when the ambient temperature and humidity are high.
The amount of sunlight, or solar radiation, that an animal is exposed to also impacts their level of heat stress. Cattle can often adequately dissipate heat overnight when temperatures are cooler, but high nighttime temperatures can cause cattle to suffer the ill effects. Whatever the cause, heat stress is an economic and animal welfare concern.
It begins at the cellular level
The key to making management interventions is to make the necessary changes before the onset of heat stress. Because both genetics and environment play a role in the performance of an animal, it is important to consider both options in addressing heat stress.
As with any type of genetic selection and planning, this is a long-term process that requires commitment and consistency to be effective. While there are likely to be a multitude of new tools forthcoming in the next few years, there are some options currently available to address heat stress utilizing genetics.
One of the simplest opportunities for commercial cattlemen is the use of mating systems to address heat stress. Mating systems can be utilized in two simple ways to address heat stress: first, manage coat color in the cow herd to reduce or eliminate darker coat colors, which absorb more solar radiation, and second, introduce genetics from tropically adapted cattle (either Bos indicus or Bos Taurus).
Although inheritance of coat color can get tricky when dealing with spotting patterns and similar markings, alteration of predominantly red or black coat colors is relatively straightforward. Introduction of germplasm from tropically adapted animals is a very quick way to confer heat tolerance in a single generation, though accumulation of genetics from adapted breeds in the cow herd will take longer with normal replacement rates. The amount of adapted-breed germplasm introduced can be managed through the use of composites or breeds that integrate adapted germplasm, generally Brahman.
While the optimum level of adapted-breed germplasm to include in your herd to confer heat tolerance is likely different for every operation, it is an opportunity to easily confer greater heat tolerance in a relatively short time period.
Influencing thermotolerance
Additionally, we can use genetics to combat heat stress by selecting traits that influence thermotolerance. One such example is hair shedding. The ability of cows to shed their winter coat is heritable, and studies have shown that animals that shed earlier also have calves with higher weaning weights.
Hair shedding phenotypes can be easily recorded early in the summer, and selection decisions can be made to favor those animals that have a greater proportion of their winter hair coat shed at an early time point. More tools are likely forthcoming in the next few years that will enable producers to select for greater thermotolerance.
As with any selection decisions you initiate in your herd, they are not made in a vacuum – making changes in one trait can cause unintended consequences in other traits that share a genetic correlation. Sometimes these changes are favorable, such as with hair shedding and weaning weight, and sometimes they are undesirable.
Genetic antagonisms, or undesirable changes, between heat tolerance and production traits in beef cattle have not been thoroughly researched. However, research in the dairy industry would suggest that there are likely genetic correlations between heat tolerance and important production traits, such as fertility and milk production, which must also be considered.
These genetic antagonisms can be overcome by selecting for increased genetic merit for both heat tolerance and all production traits that are important to your operation, or by using a selection index that includes production traits as well as heat tolerance.
Heat stress is an important issue in the beef industry, particularly given that cattle spend the majority of their lives outdoors and exposed to the elements. Now is the time to develop your plan before the onset of heat stress takes you by storm. In doing so, you can help ensure optimum performance and well-being for your beef cattle herd. 
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Megan Rolf
- Assistant Professor
- Animal Breeding and Genetics
- Kansas State University
- Email Megan Rolf
PHOTO: Heat stress can be mitigated using a variety of management interventions in a controlled setting. However, for cattle on pasture, it is a little more difficult to intervene – that's where genetics come into play. Staff photo.
