As herds continue to expand, reproductive efficiency has decreased in the last decades in U.S. dairy operations. A combination of different factors can greatly influence reproductive performance. Inaccurate heat detection is costly, and often the weak link in a dairy’s breeding program. Research indicates that an average of 5 to 25 percent of cows are not in heat at the time of insemination.

Heat stress is a major factor contributing to low fertility that has been quantified and studied. A heat-stressed cow minimizes physical activity, thus signs of estrus become less pronounced. When the cow can no longer regulate her body temperature, feed intake declines, milk production reduces and reproduction is compromised.

Heat-stressed cattle expressed estrus for 4.5 hours less than non-stressed cattle. In addition, the frequency of mounting decreases during the hotter months of the year by nearly half. Lower pregnancy rates may result from reduced ability of the cow to support a viable embryo.

As a result of the temperature and blood variations in the uterus, the probability of early embryonic death increases. The use of embryo transfer in dairy cattle has shown beneficial outcomes in improving fertility, especially during heat stress periods. The transfer of an embryo could bypass certain causes of infertility (embryonic death, egg/sperm damage and fertilization problems).

Successful pregnancy depends upon the presence of a viable embryo in the uterine horn with a functional corpus luteum (CL), prior to the maternal recognition of pregnancy. Embryo transfer occurs 6 to 7 days after a recipient cow has been detected in standing estrus.

In a study conducted in Florida to prove that using embryo transfer rather than A.I. could improve summer reproductive performance, conception rates at Day 42 were higher for embryo transfer cows (A.I. at 21.4%, E.T. at 35%).

An embryo transfer program should be carried out during cool seasons. To be successful, donors must be producing consistent, quality eggs, technicians must be highly skilled, and recipients must be in good body condition with a proven reproductive record.

The use of an E.T. program can serve as a supplement to your regular A.I. program in order to maximize the reproductive performance of your herd.  EL

References omitted due to space but are available upon request.

	Dr. Carlos Tellez AltaPreg Specialist This e-mail address is being protected from spambots. You need JavaScript enabled to view it