Gene Editing Could Improve Heat Tolerance
The detrimental health, well-being, and productivity effects of heat stress in dairy cattle could one day be partially solved through gene editing.
The currently experimental technology removes an undesirable genetic trait in an animal and replaces it with a more favorable one at the genome level, known among researchers and regulators as an “intentional genomic alteration” (IGA). It is possible to introduce traits within a species, and between species.
In the case of heat stress, two approaches are being taken by researchers to help cattle cope:
Slick hair coat gene – Some cattle have a shorter and shinier hair coat that makes them more comfortable in high-heat environments and thus less susceptible to heat stress. This unique hair coat is the result of the dominant “slick” gene, which originates from the Senepol breed.
A collaborative project between researchers at Mississippi State University and the University of Puerto Rico studied 84 Holsteins with the naturally occurring “slick” gene. They found that the animals had lower body temperatures, lower respiration rates, and improved reproductive efficiency in tropical conditions, compared to herd mates with traditional hair coats.
Using a technology called CRISPR-Cas9, researchers in many parts of the world, including the United Kingdom, New Zealand, and the U.S., have successfully produced cattle with the slick coat gene. Semen from some sires that are homozygous for the slick gene through conventional breeding also is currently available.
Hide color alteration – New Zealand researchers are exploring how gene editing can dilute the jet-black hide color of Holsteins to make them less susceptible to heat stress. They said black absorbs more solar radiation, contributing to heat stress.
In their study, they used gene editing to swap the black gene in Holsteins with the semi-dominant color dilution phenotype from Galloway and Highland cattle. The resulting calves carried a typical, spotted hide pattern, but instead of black, the darker pattern areas were a silvery gray color that would attract less heat.
Developers of gene-editing technology emphasize that the process simply takes traits already occurring in nature and shares them with other animals, thus exponentially accelerating genetic progress for that trait. In the case of heat stress, they emphasize environmental advantages along with animal health, comfort, and productivity.
Once an animal receives the IGA, it is passed on to future offspring, making it possible to replicate the trait via conventional breeding. In March 2022, the FDA approved the first IGA for animals intended for food production by making a “low-risk determination” for two genome-editing beef cattle created with the slick hair coat.
The FDA declared the animals and their offspring safe for human consumption. Acceligen, the company that developed the slick-coat cattle, is now free to market the cattle, their genetic material, and their offspring, without further regulatory approval.
But in the U.S., the commercial application of gene editing still is subject a case-by-case approval process. Dr. Steven Solomon, director of the FDA’s Center for Veterinary Medicine, said, “We expect that our decision will encourage other developers to bring animal biotechnology products forward for the FDA’s risk determination in this rapidly developing field, paving the way for animals containing low-risk IGAs to more efficiently reach the marketplace.”
For more on heat stress, read:
- Beating the “Summer Slump”
- Feeding Strategies to Mitigate Heat Stress
- Pour Hydration to Heat-stressed Calves
- Keep Cow Handling to a Minimum During Hot Weather
