Researchers at the university of wisconsin have found a gene that causes embryonic death in cattle around the fifth day of pregnancy. And they believe this lethal gene may help explain why pregnancy rates have dropped significantly over the past 20 years.

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. Research data show the frequency of the gene in heterozygous form — where a cow carries both the lethal variant and the non-lethal variant — is as high as 50 percent among Holsteins.

Additional research is under way to better understand the gene, and also to develop testing procedures that will help prevent undesirable matings.