Increasing pregnancies following synchronization of bovine recipients
Anim Reprod, vol.9, n3, p.312-317, 2012
The success of a commercial embryo transfer program depends on the production of high numbers of viable embryos from donor cows that result in high numbers of calves born when the embryos are transferred to suitable recipients. In recent years, a great deal of effort has been devoted to the development of treatment protocols that permit the efficient use of recipients and result in high pregnancy per recipient synchronized, especially in recipients managed on pasture. One of the most successful alternatives to increase the number of recipients utilized in embryo transfer programs is the use of protocols that allow for embryo transfer without the need for estrus detection, usually called fixed-time embryo transfer (FTET). Pregnancies to FTET have been reported to be similar to those after detection of estrus, but the overall proportion of recipients pregnant over those synchronized are higher because these treatments have increased the proportion of recipients that receive embryos. Treatments that increase progesterone concentrations and pregnancies per embryo transfer have also been investigated in recent years. Most of these treatments have resulted in increased pregnancy per embryo transfer in recipients with Bos indicus influence, while benefit were not so obvious in Bos taurus recipients managed under more optimal conditions. While factors such as the reproductive history of the recipients and the stage and quality of embryos may affect pregnancy per embryo transfer, other factors such as estrus detection and the time interval from thawing to transfer do not seem to affect the proportion of recipients pregnant with embryos frozen in ethylene glycol and transferred at a fixed-time.
eCG, fixed-time embryo transfer, GnRH, hCG progesterone