In other words, it’s an accelerated form of selective breeding – and some in the field hope it will be a game changer. They argue that gene-edited animals with mutations swapped around within their own species are less risky than traditional transgenic animals and therefore should not have to clear the same regulatory hurdles. Some even argue that they should not be regulated at all.

One thing is clear: such debates remain theoretical until researchers come up with a more compelling case than fast-growing salmon. “We need to produce animals with real and distinct benefits that can’t be produced any other way,” says Whitelaw, “then we can ask society, ‘Do you want it?’”

Whitelaw is using genome-editing tools to make European domestic pigs resistant to a deadly viral disease called African swine fever, for which there is no vaccine. Wild pigs in Africa are resistant to the disease but they cannot be crossbred with European domestic pigs. So Whitelaw and his colleagues pinpointed a tiny genetic variation that they think bestows resistance – a mutation in a single base pair among three billion – and precisely replicated it in the fertilised eggs of a European domestic pig. In October 2013, Whitelaw’s team announced the birth of five pigs carrying the mutation. It remains to be seen how these GM pigs cope when infected with the virus. But if they are resistant, the benefits are clear. “It would be good news for the animals and good news for producers,” says Whitelaw.

Tweaking the genomes



Across the Atlantic, Scott Fahrenkrug is betting that hornless cattle can serve up a similar win-win situation that will finally push a GM animal into mainstream farming. In 2010, Fahrenkrug, a molecular geneticist then at the University of Minnesota, saw a TV news story about how farmhands use hot irons to burn off horns from dairy cows. The practice is necessary to stop the animals from injuring their handlers and each other, but it’s also painful for cows and expensive for farmers. “It’s a pretty nasty practice and everyone wants to get rid of it,” says Fahrenkrug. But it would take decades to produce hornless dairy cattle with conventional selective breeding methods.

Instead, Fahrenkrug’s St Paul, Minnesota-based startup Recombinetics is tweaking a few letters in the genomes of dairy cattle to render them hornless, while maintaining cherished milk-production qualities. They precisely edit the DNA of cells from Holstein bulls – prized for producing huge amounts of milk – to replicate the letters that make Red Angus cattle – a breed prized for beef – hornless. The researchers then use cloning to transform edited cattle cells into embryos, or direct embryo editing, to produce hornless calves.