Dairy owners want to get the most out of their cows, so they do their best to breed cows that will provide the most milk. This leads managers to select breeding material from bulls with offspring that generate a lot of milk.
But that’s created an issue. Almost every dairy owner selects breeding material from just two bulls that lived decades ago.
Chad Dechow, a geneticist at Pennsylvania State University who studies dairy cows, and some of his colleagues at Penn State made a discovery that shocked a lot of people. All the Holstein bulls that farmers were using could trace their lineage back to one of just two male ancestors.
“Everything goes back to two bulls born in the 1950s and 1960s. Their names were Round Oak Rag Apple Elevation and Pawnee Farm Arlinda Chief.”
The breeding material, semen, for these two bulls comes from Select Sires, one of the few companies to traffic in such an item.
Dairy farmers go online, look through the list of bull material available and how much produce, or milk, on average comes from their daughters. It seems obvious that dairy farmers would overwhelmingly choose the most productive ones, so they end up with the same bulls.
This doesn’t mean most diary cows are the same because they have many different mothers. But they do share 50% of genetic material, which has weeded out some traits that existed in bulls in years past.