Daughters born to a bull that was himself born in 1962 produced so much milk that this bull, called Pawnee Farm Arlinda Chief, has millions of descendants, but along with that increase in milk production came a hidden lethal mutation, the Atlantic reports. Still, it notes that though spontaneous abortions of some of the Chief's descendants cost the dairy industry $420 million in losses, using his sperm led to an increase of $30 billion dollars in milk production.
About 10 years ago, dairy farmers and the US Department of Agriculture began to combine genetic marker and milk production data to gauge whether a young bull might have wanted characteristics. (GenomeWeb wrote about this use of SNP chips in dairy cow breeding a few months back, here.) The Atlantic notes that during this time, USDA researchers noticed that when two descendants of the Chief were crossed, there was one marker that their offspring never had two of.
By sequencing the Chief and one of his sons, University of California, Davis's Harris Lewin and his team found that this marker was near the Apaf1 gene, which, when mutated in mice, leads to out-of-control growth of brain cells in utero and embryonic death. It's now being screened for among dairy cows, the Atlantic notes, and its frequency has fallen.
"Genetics has transformed breeding in the dairy industry, making it easier to spot patterns like Apaf1's lurking in the genetic pool," the Atlantic adds. "And dairy cows will become better and better optimized milk-making machines."