Cosmo the Bull Calf Has Been Genetically Engineered to Produce 75% Male Offspring

The bull was genome-edited as an embryo using CRISPR technology in a scary kind of experiment.
Loukia Papadopoulos

Genetic engineering can produce some pretty scary results. Just recently, scientists at the University of California, Davis, developed a bull calf, named Cosmo, who is capable of producing 75% male (or at least male-looking) offspring.


The bull was genome-edited as an embryo using CRISPR technology. This method allows researchers to make targeted cuts to the genome or insert useful genes. 

In Cosmo's case, scientists successfully inserted the cattle with the SRY gene. This gene controls the development of male features. The experiment marks the first demonstration of a targeted gene insertion for large sequences of DNA via embryo-mediated genome editing in cattle and it is made to produce cattle that look like males.

“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.

As scary as the procedure may be, it could prove beneficial for the environment. Male cattle are about 15% more efficient at converting feed into weight gain, making them more fuel-efficient than females.

“Ranchers could produce some females as replacements and direct a higher proportion of male cattle for market,” said Joey Owen, a postdoctoral researcher in animal science who is leading the project with Van Eenennaam.

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The project took two and a half years to develop the method to insert a gene into the developing embryo. It then saw another two years dedicated to successfully establishing a pregnancy.

And it is just the beginning of the researchers' work. When Cosmo reaches sexual maturity in a year, he will be bred to study if the experiment was indeed successful in producing offspring that will grow to look like males.

Cosmo and his offspring, however, will never enter the food supply. This is because the Food and Drug Administration regulates gene-editing of animals as if they were drugs.

What do you think of this initiative? Can it lead to a more environmentally friendly production of beef or is it a scary development in genetic engineering?

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