CRISPR genome editing has been used to create a cow with grey patches instead of black, meaning it will absorb less heat. The aim is to reduce heat stress in the animals due to global warming聽鈥� which, ironically, is in no small part due to emissions and deforestation from cattle ranching.
鈥淕enome editing is a promising approach to rapidly improve and adapt livestock to changing environmental conditions,鈥� says Goetz Laible at AgResearch in New Zealand. 鈥淥n a global scale, even modest improvements in productivity from colour-diluted cattle would translate into substantial environmental benefits.鈥�
New Zealand dairy cows already become heat stressed for nearly 20 per cent of the time they are being milked, which can halve yields. Heat also reduces fertility, says Alison Van Eenennaam at the University of California, Davis. 鈥淚t鈥檚 hard to get them pregnant during the heat.鈥� Dairy cows also need to have a calf every year or so to maintain milk production.
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Cattle with black or mostly black coats, like Holstein Friesian dairy cows, are thought to suffer more from heat stress. So Laible and his colleagues decided to find out if they could benefit from lighter coats like those of some Highland beef cattle, caused by a tiny change in a gene involved in pigmentation called PMEL.
Using standard breeding techniques to cross beef cattle with dairy cattle would result in offspring that weren鈥檛 ideal for producing either milk or meat. Instead, Laible鈥檚 team used CRISPR to change the PMEL gene in fetal skin cells from a male Holstein Friesian that were growing in a dish.
The researchers then used cloning to generate embryos for implantation. Two聽calves were born, with dramatic changes in coloration (pictured above).
One calf had to be put down after birth and the other died of an infection when it was four weeks old. These health issues are thought to be result of the cloning process, rather than the genetic editing.聽Cloning isn鈥檛 necessary to produce CRISPR-edited cows, so the team will avoid it when they create more calves with this edit, says Laible.
Peter Hansen at the University of Florida and his colleagues have shown that predominantly white cattle regulate body temperature better and have a lower reduction in milk yield than predominantly black cattle. So the New Zealand team鈥檚 approach could work, he says. 鈥淏ut, at least for cows with access to shade, the effect might be small.鈥�
Other teams are creating more heat-tolerant cattle by introducing a gene variant for shorter hair. The 鈥淪lick mutation鈥� has already been introduced into some Holstein cows via normal breeding.
A US company called Recombinetics has also gene-edited this trait into Angus beef cattle. The first calf, called Genzel, was born in Brazil on 14 July 2018.
Angus beef cattle produce twice as much meat as the Nelore breed popular in Brazil, but can鈥檛 cope with tropical heat. In theory, heat-tolerant Angus cattle could double Brazil鈥檚 beef production without increasing the environmental impact.
The world鈥檚 1.5 billion cattle are experiencing more heat stress because of global warming, but they are also a major cause of climate change, with livestock farming聽producing about 18 per cent of global greenhouse gas emissions. Rising demand for milk and beef in places like China is also driving deforestation to clear land for cattle ranches or farms to grow cattle feed.
Itzhak Mizrahi at Ben-Gurion University of the Negev in Beersheba, Israel, and his colleagues have shown that some cattle have more efficient microbiomes that turn more food into useable compounds rather than methane. 鈥淵ou get more from each bite of the cow,鈥� he says.
His group and many others hope to reduce methane emissions both through cattle breeding and by manipulating their microbiomes. Reducing demand for meat and milk would be the simple solution, says Mizrahi, but with global demand still rising, it is important to try to reduce the environmental impact.
Reference: bioRxiv, DOI: 10.1101/2020.09.15.298950
