Researchers at the University of Wisconsin have found a gene that causes embryonic death in cattle around the fifth day of pregnancy.

In the last 20 years, there has been a 20 percent drop in pregnancy rates in Holstein dairy cattle, says Hasan Khatib, assistant dairy science professor at the University of Wisconsin. “Based on our preliminary data for in-vitro fertilization experiments, we believe these problems can be attributed to this gene.”

The gene is only lethal when it’s homozygous — that is when both parents contribute the lethal gene variant to their offspring.  However, the gene is fairly common in non-lethal combinations. Khatib’s data show the frequency of the gene in it heterozygous form — where a cow carries both the lethal variant and the non-lethal variant — is as high as 50 percent among Holsteins.

The gene is common for a reason. It also increases milk production and milk fat and protein content.

“We don’t want to eliminate the lethal variant because it is linked with milk production traits, but we want to eliminate the homozygous effect that causes early embryonic death,” says Khatib.

Since this condition only occurs if both parents carry the gene (in that case, the odds of getting a homozygous embryo are 25 percent) the solution is to avoid breeding heterozygous cows to heterozygous bulls.

Additional research is underway to better understand the gene. And develop testing procedures to prevent undesirable matings.

University of Wisconsin