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Tackling Heat Tolerance

The development of a hair shedding EPD could become an economic driver for selecting Angus cattle more tolerant to heat and fescue.

It’s no secret cattle perform better in colder climates, but a new expected progeny difference (EPD) developed by Angus Genetics Inc., (AGI) is expected to be a game-changer for Angus breeders in regions with warm climates and abundant fescue.

“The hair shed EPD will be important for breeders selecting on animals more tolerant to heat and fescue,” says Kelli Retallick, director of genetic and genomic programs at AGI. “Developing hair shedding scores has allowed breeders to focus on adapting animals to their environment.”

Breeders will be able to select for cattle that have a more viable hair coat for regions with extreme climates, such as the Southeast, as the EPD correlates to beef cattle thermoregulation.

“Hair shedding is going to be important not only for the breeders who have cattle in those southeast regions, but for the folks who buy those cattle,” Retallick says.

Esther McCabe, director of performance programs at AGI, says the hair shedding EPD is developed much like claw set and foot angle EPDs were.

“Producers collect and report scores,” McCabe says. “Those scores are put into performance programs, and then are calculated into an EPD. Those visual scores range from one to five.”

When appraising hair shed scores, a score of 5 correlates to full winter coat retention; whereas a 1 correlates to being completely slicked off. Thus, the scores are as follows: 5, 0% shed out; 4, 25% shed, lost winter coat on head and neck; 3, 50% shed, has also lost hair along topline and brisket; 2, 75% shed, hair remains on flank and belly; 1, 100% slicked out. Breeders are advised to collect scores between mid-

April and mid-June.

In terms of shedding out, the correlation between scores and ages can be related to a U shape. Young cattle tend to receive higher scores, middle-aged and mature cattle receive low scores, and old females (10-12 years of age) receive higher scores. When collecting hair shedding scores, AGI primarily receives scores for middle-aged females. Yearling cattle are the youngest age scores can be collected.

Hair, heat stress and return on investment

According to an article about genetic selection evolution , economic losses in 2003 due to heat stress in cattle totaled more than $360 million. In 2020 this number would equate to an estimated $518 million after an adjustment for inflation.

McCabe says hair shedding is a moderately heritable trait that can continue to improve through genetics and EPD selection. She also says to maintain homeostasis (normal levels), the body of any mammalian species will redirect energy expenditure to do so.

“When cattle are heat-stressed, their energy expenditure while trying to cool off results in blood flow going to the skin, attempting to dissipate heat,” McCabe says. “By doing so, the energy required for these tasks is not capitalizing on normal bodily functions.”

Heat stress can result in reproductive losses such as open cows, females that aren’t cycling and slipping calves. Reduction of feed intake, decreased milk production, lack of growth and even death are also consequences of heat stress.

The hot topic

“There’s a relationship between the cattle that shed off earlier and have a tolerance to hot fescue,” Retallick says.

For breeders in the Southeast, two of the most prevalent stressors to beef cattle are heat stress and fescue toxicosis caused by grazing tall fescue infested with endophytic fungus (fungus that grows on the plant), commonly referred to as hot fungus. Hair shedding, or the rate at which beef cow sheds her winter coat, is a good indication of adaptation to heat and tolerance to fescue toxicosis. Retallick says fescue toxicosis occurs when cattle consume this endophyte-infested grass, also known as hot fescue, in a certain growing stage.

Though fescue toxicosis can be detrimental for some herds, ridding the land of the plant is not a viable option. It is expensive to clear out native grasses and implement another forage option. Additionally, fescue is a hardy grass that is very drought resistant.

“Working with the environment rather than against it has been a goal for breeders in those regions for a long time,” Retallick says. “It is more about tolerance of animals to heat and native grasses.”

From a bottom-line standpoint, McCabe says breeders should target who their customers are and what they need when developing mating schemes. The location and environment of those firms can ultimately dictate how animals will partition their energy once relocated.

Retallick says, “If people want to find cattle from different parts of the country, having something like a hair shed EPD will help buyers bring in cattle with less risk. It’ll be a good indicator for how those genetics will perform and adapt in an environment.”

She adds the development of a hair shed EPD prevents a narrowed gene pool and can serve as an appealing international marketing opportunity with breeders from equatorial, subtropical regions.

“If we want Angus cattle to become the solution for regions such as Brazil and temperate subtropical environments, the basin that holds the highest quantity of cattle in the world, we need to develop tools to allow us to select animals for those environments,” Retallick says.

The hair shed research EPD will be updated on Aug. 6, 2021. Any scores collected need to be submitted to the Association by Friday, July 30, 2021, to be included in the updated research EPD. For more information, call 816-383-5100 or email

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