In the U.S., just two Y chromosomes exist within a population of 9 million Holsteins. Researchers want to know what traits have been lost over time.

There are more than 9 million dairy cows in the United States and the vast majority of them are Holsteins. Researchers at the Pennsylvania State University looked closely at the male lines and  they discovered 99 percent of them traced back to one of two bulls, both born in the 1960s. That means among all male Holsteins in the country, there are just two Y chromosomes. If Holsteins were wild animals, that would put them in the category of critically endangered species. “It’s pretty much one big inbred family,” says Leslie B. Hansen, professor at the University of Minnesota. Genetic homogeneity isn’t good in the long term, which increases risk of inherited disorders. There is so much genetic similarity among them. “If we limit long term genetic diversity of the breed,” Chad Dechow says, “we limit how much genetic change can be made over time.” The females haven’t fared much better. “What we’ve done is really narrowed down the genetic pool,” says Dechow. The biggest change has been in the way cows are bred. Long ago, farmers would bring in bulls from other farms to get their cows pregnant — a way of ensuring genetic diversity as Hansen says. In 1940s, they began to use artificial insemination. Soon, technology allowed semen to be frozen. In 2009, new technology came along: big data and genomic selection determined by computer which called lifetime net merit. It represents the average amount of money farmer can expect to earn over the offspring’s life by choosing this bull over another one. The process also led to even higher rates of inbreeding. Fertility rates are affected by inbreeding and already Holstein fertility has dropped significantly. Pregnancy rates in the 1960s were 35 to 40 percent, but by 2000 had dropped to 24 percent.“Something needs to change,” Hansen says. What had been lost with all this inbreeding? That required digging into the archives of the National Animal Germplasm Program and began searching out some of those old genes. Dechow’s team found two samples that weren’t related to Chief or Elevation and created embryos. Dechow can already see a difference on the ground in the way these cattle look. Dechow is still hopeful that there will be more to gain from this research once the cattle mature.This article was originally published on Undark. Read the original article.