Modern dairy cows have been bred for maximum milk production. But their higher metabolism also makes it difficult for them to rid themselves of excess heat. And high body temperatures make successful reproduction extremely difficult. First, heat-stressed cows do not display signs of estrus, so farmers have no way of knowing when to artificially inseminate them. And even if the cow is successfully inseminated, heat stress more than likely will result in an unsuccessful pregnancy.
Embryo transfer involves implanting an in vitro embryo into a cow.
The in vitro embryos have been produced in the lab and protected from heat during the critical first week of growth. Thatcher and Dr. Maarten Drost, in the College of Veterinary Medicine's large animal clinical sciences department, have shown that transferring embryos during the summer increases pregnancy rates. However, frozen embryos have a low survival rate, so freshly fertilized embryos must be used. That drives the cost up. Antioxidants may offer another approach to increasing pregnancy rates in the summer.