Average summer temperatures and the frequency of ‘severe heat days’ are rising in several regions of the globe.
Dairy animals on pasture are hence more susceptible to heat stress. Smaller cow breeds, such as the Guernsey, outperform larger ones, such as the Holstein, although coat type and colour also have a factor.
So far, there are two ways to modify the coat via gene editing to boost heat tolerance. First, consider the’slick coat,’ which consists of short, silky, and occasionally even shiny hair.
The characteristic of a slick coat
Holsteins with a smooth coat have superior heat tolerance, as seen by lower internal (vaginal) temperatures and respiration rates. Researchers from Mississippi State University and the University of Puerto Rico in Mayagüez released a report in 2020 concluding that under the hot and humid circumstances of Puerto Rico, Holstein cows with the slick gene outperform those without it in terms of reproduction.
When compared to qualities including several genes, the smooth trait involves a single dominant gene, making it ideal for gene editing. According to Dr Alison Van Eenennaam, a scientist at the University of California, Davis, gene editing entails directing enzyme’scissors’ to make a targeted, particular cut in a DNA sequence. “Depending on how that’s repaired, you can have inactivation of the gene located at that point on the strand, or a difference in how the gene functions,” she adds. “DNA from that organism, another of its species, or another species may also be introduced.” Van Eenennaam employed gene editing to make a bull calf with more than 50% male progeny.
The’slick coat gene’ was introduced into freshly fertilised eggs from cows lacking the gene by geneticists at the Roslin Institute (University of Edinburgh in Scotland). Modified embryos were implanted in surrogate mother cows, and calves with glossy coats (but no other alterations) were born.
The research believes that applying this gene change has a high potential for increasing cow herds that are better acclimated to heat stress across the globe, and that it would be particularly beneficial to small-holder farmers in tropical nations. They are currently collaborating with colleagues at Kenya’s International Livestock Research Institute on local cow breeds.
According to team member Dr. Appolinaire Djikeng, “we can do small edits in the genome that very quickly accomplish improvements that would otherwise take 20 generations.” “I am very excited about the potential application of this technology in Kenya, the United Kingdom, and other parts of the world.”
Another clever gene editing experiment
Meanwhile, a company in the United States called Recombinetics has utilised gene editing to create two beef calves with the smooth coat feature. The US Federal Drug Administration (FDA) issued its first verdict on gene-edited cattle pertaining to this gene modification in March 2022, calling it a ‘enforcement discretion determination.’ This implies that the FDA judged that the ‘risk’ connected with these calves and their gene edit was minimal, therefore they are exempt from the implementation of current US gene editing restrictions. The FDA now defines any genetic mutation to an animal by gene editing as a novel animal medication, and so US drug regulation standards apply. In the future, gene-edited animals in the United States may be governed by the US Department of Agriculture rather than the FDA, which now controls gene edits to plants that include the inactivation of a gene or any gene that may have been introduced via normal breeding.
Van Eenennaam speculates that “the FDA could consider a tiered system with risk levels.” And it will be shortly. We must keep in mind that postponing gene editing research and commercialization comes at a high cost.”
Other nations, like Brazil, Australia, and Argentina, see gene editing as regular breeding when a gene is knocked out and no new DNA is introduced.
Dr. Tad Sonstegard, President and CEO of Acceligen (owned by Recombinetics), said that the company would continue to work towards the commercialization of cows with the slick gene modification in the United States.
More heat with a black coat
Changes in coat colour are another method gene editing is being utilised to minimise heat stress in cattle. Unlike other light-colored dairy breeds such as Jersey, the Holstein cow has a black and white coat, with some of the breed having a lot of black – and dark colours absorb substantially more UV radiation than lighter.
A team of geneticists in New Zealand has previously done this with Holsteins, utilising a gene modification to eliminate the black coat hairs. The AgResearch, Ruakura Research Centre, University of Auckland, Auckland, Maurice Wilkins Centre for Molecular Biodiscovery, Massey University Manawatu, and the Livestock Improvement Corporation are all part of the team.
They explain in their research that they induced a deletion in Holsteins in “the pre-melanosomal protein 17 gene, which has been proposed as the causative variant for the semi-dominant colour dilution phenotype observed in Galloway and Highland cattle.” Calves born from cells with homozygous edits have a unique grey and white coat pattern.”
“While we have demonstrated it for a dairy breed, the strategy could easily be applied to beef breeds such as Black Angus,” they say. Overall, our research demonstrated and confirmed genome editing as a viable new strategy for rapidly adapting cattle to changing environmental circumstances.”
Other genes associated with heat
Meanwhile, experts at Agriculture Victoria in the Australian state of Victoria have found many genes highly connected with heat tolerance.
Since 2017, Dairy Australia and the country’s dairy industry have made genomic breeding values for heat tolerance accessible to dairy producers via DataGene, an independent entity administered by Dairy Australia and the dairy industry.
