Genetic Counseling for Cows

When UW-Madison hired Hasan Khatib as an assistant professor in 2002, his colleagues knew not to expect a typical dairy scientist. A student of human genetics, Khatib had spent three years after earning his doctorate counseling couples about their chances of passing on inherited disorders.

These days, he’s working with a different species—but he’s still doing essentially the same thing.

In his lab, Khatib studies the genes of newly fertilized cow embryos to understand the connections among traits passed down from their parents. For the past several years, he’s been focused on a major frustration for the dairy industry—the fact that today’s super-producing milk cows often have trouble getting pregnant. In fact, during the past 20 years, as milk yields have gone up, pregnancy rates have headed in the other direction, falling by 20 percent.

“A large portion of infertility is because embryos die early, in the first few days of pregnancy,” says Khatib. “That’s why we are focused on this stage of development, where we can identify genetic factors leading to better survivability of embryos, hence increasing fertility of cows.”

Khatib has discovered one reason why increased milk production and infertility go hand-in-hand. He located a gene variant that, when present in homozygous form—two copies, one from each parent—the embryo dies soon after conception. But in heterozygous form, where the cow carries one lethal and one non-lethal variant, the gene is associated with increased milk production.

Because breeders select for higher milk production, Khatib’s data suggests that 65 to 70 percent of Holsteins have that genotype. Breeding heterozygous bulls with heterozygous cows, however, increases the chance of passing on the lethal combination of genes. To avoid that situation, Khatib developed a set of markers that indicate the presence of the gene, which he has patented and licensed to a breeding firm.

“This is like genetic counseling for bulls,” he says. “It’s the same principle: How to use your genetic markers to improve the trait that you’re looking at.”