Reengineering Life is a series from Future Human about the astonishing ways genetic technology is changing humanity and the world around us.
If we want to survive as the planet gets hotter, the animals we rely on for food will need to adapt to climate change. Some scientists think they can speed up that adaptation using gene editing.
One problem that farmers face is heat stress in dairy cattle, which happens when cows are exposed to high temperatures for too long. Cows that are heat stressed eat less, make less milk, and have a hard time conceiving. In hot temperatures with high humidity, heat stress can even cause death. In the United States, heat stress costs the dairy industry $900 million a year or more, and in the developing world, where small farmers rely on just a few animals for their livelihood, the impact can be devastating. As temperatures rise globally, heat stress is likely to only get worse.
“This is not only markedly reducing milk production but also affects the cows’ well-being and fertility,” Goetz Laible, PhD, an animal scientist at New Zealand’s AgResearch, a government-owned company that conducts research to benefit the country, tells Future Human. “Rising temperatures and predicted longer and more intense periods of warm weather can only mean that the problems with heat stress and fertility will increase.”
Laible and his colleagues recently took a unique approach to addressing this issue: They tried to change the color of cows’ coats using genetic engineering.
Because darker-colored animals absorb more heat from sunlight, they’re thought to be more affected by warmer temperatures than lighter-colored animals. As Laible and his colleagues describe in a paper recently posted to the preprint server bioRxiv, they sought to lighten the coats of Holstein-Friesian cattle — the quintessential dairy cows known for their white coats with patches of black — to make them more resilient to our changing climate.
Using the gene-editing tool CRISPR, the researchers altered a pigmentation gene called PMEL in cattle embryos in a lab. The genetic variant they created exists naturally in some beef cattle breeds like Galloway and Highland cattle and gives their coats a silvery gray color instead of black or brown.
The researchers then cloned the embryos before implanting them into surrogate mother cows. Cloning is used in agriculture to make copies of the best animals, which improves the overall quality of animal herds, but it’s risky. Cloned animals can be born with defects and have long-lasting health problems.
The scientists transferred 22 edited embryos into surrogate mother cows, and three became pregnant. Two of them gave birth to calves with markedly lighter coats with silvery gray spots instead of jet black. Unfortunately, the two calves didn’t live long enough for researchers to determine whether the lighter coats would be more protective against heat stress. One of the calves had to be put down shortly after birth because of health complications, and the second was healthy at birth but died at four weeks due to an infection.
Laible says the health issues are “well-known complications” associated with cloning technology and likely not due to the editing. This DNA alteration doesn’t cause health issues in cows that naturally have it, he says. For that reason, it shouldn’t affect the milk these cows produce.
One concern over using CRISPR in embryos is the potential for editing mistakes, including “off-target” effects — unintended edits that happen at other places in the genome. Laible says his team didn’t find any evidence of off-target edits in the DNA of the two calves that were born.
Coat color is just one biological contributor to heat stress in cattle. Hair length also plays a role. One company, Minnesota-based Acceligen, is using gene editing to instill a different mutation called the “slick” trait to make cattle more heat resistant. This naturally occurring genetic variant is responsible for short, sleek hair in cattle that helps keep them cool in subtropical heat.
Acceligen’s CEO Tad Sonstegard, PhD, tells Future Human that the company has used gene editing to produce two cows with this slick trait and has several pregnant surrogates carrying genetically altered fetal cows. The company has received funding from the Bill & Melinda Gates Foundation to eventually bring these cows to farmers in sub-Saharan Africa, where cattle herds are less productive because they haven’t benefited from the kind of selective breeding that’s done elsewhere. The company also has plans to introduce these cows in South America and eventually the United States.
Sonstegard says in some cattle species naturally adapted to heat, like Zebu cows that originated in South Asia, many genes appear to be linked to the adaptation.
Bhanu Telugu, PhD, an animal scientist at the University of Maryland and president of the animal biotech company RenOVAte Biosciences, tells Future Human that one edit is a good first step, but additional edits may be able to boost heat tolerance even more.
“My expectation is that, going forward, there would be a host of two or three edits that would be stacked on to make ‘super calves,’ so to speak,” Telugu, who wasn’t involved in the New Zealand study. “As temperatures keep increasing, these animals are under increasing stress, so being able to bring those traits into these animals, either by breeding or by genetic engineering methods, would be extremely important.”
Next, Laible plans to work on introducing genetic variants from tropical cattle that have been associated with heat tolerance and resilience to disease.
Critics of genetically modifying animals may be quick to point out that reducing heat stress in animals can be done without the need for gene editing. Shade, proper ventilation, and access to clean water are all currently used to prevent heat stress.
And of course, cows themselves generate greenhouse gas emissions, which are driving climate change. While humans are unlikely to end their reliance on cow milk anytime soon, gene editing could potentially help cattle be more productive in the future, helping us raise fewer animals for the same amount of milk.