Meet Cosmo, a Bull Calf Designed to Produce 75% Male Offspring

Scientists at the University of California, Davis, have successfully produced a bull calf, named Cosmo, who was genome-edited as an embryo so that he’ll produce more male offspring.

Using the genome-editing technology CRISPR, researchers can make targeted cuts to the genome or insert useful genes, which is called a gene knock-in.  In this case, scientists successfully inserted or knocked-in the cattle SRY gene, the gene that is responsible for initiating male development, into a bovine embryo. It’s the first demonstration of a targeted gene knock-in for large sequences of DNA via embryo-mediated genome editing in cattle.

“We anticipate Cosmo’s offspring that inherit this SRY gene will grow and look like males, regardless of whether they inherit a Y chromosome,” said Alison Van Eenennaam, animal geneticist with the UC Davis Department of Animal Science.

Van Eenennaam says part of the motivation to produce more male cattle is that male cattle are about 15 percent more efficient at converting feed into weight gain. They are more fuel-efficient than females. Additionally, they tend to be processed at a heavier weight. It could also be a win for the environment, with fewer cattle needed to produce the same amount of beef.

“It took two and a half years to develop the method to insert a gene into the developing embryo and another two years to successfully establish a pregnancy,” said Owen. But in April of 2020, a healthy 110-pound male calf was born.