Can't have your cake and eat it, too - that's the lesson behind a newly discovered gene mutation in dairy cattle that simultaneously increases milk yield and decreases fertility.

For years now, Scandinavian dairy cattle have been enjoying a heyday in terms of milk production, the combined result of targeted breeding programs and modern breeding methods. Efforts to increase fertility have been far less successful, however, with rates largely remaining stagnant.

The deleted gene sequence, discovered by researchers from five different European institutions, appears partly to blame. The recessive mutation works by causing calf fetuses to die while still in the embryonic stage. They are then either aborted or the whole thing is registered as a failure to inseminate.

"Our study demonstrates that embryonic lethal mutations account for a non-negligible fraction of the decline in fertility of domestic cattle and that associated positive effects on milk yield may account for part of the negative genetic correlation," said Goutam Sahana, a co-author of the study from Aarhus University.

The mutation has become relatively common in Nordic Red cattle, probably in part because breeders have accidentally been passing it on in their efforts to breed cows with high milk yields. However, in other breeds, such as the Nordic Holstein and Danish Jersey populations, the mutation appears to be absent.

"The fact that the mutation is recessive means that both parents must carry it and pass the genes on to their calf for the calf to be affected," Sahana said. This fact, the researcher explained, could be used to open the door to increased fertility.

"The bulls carrying the deletion can be routinely identified in on-going genomic selection program and by avoiding carrier-by-carrier matings a quantum jump in fertility could be achieved in Nordic red breeds," he said.

The study was published in the journal PLOS Genetics.