Superovulation and Embryo Transfer in Cattle

By

Dr. Daniel Ryan, Reprodoc Limited,

Cullenagh, Fermoy, Co. Cork. 
 

Superovulation and embryo transfer arose from the need to harvest genetics from superior females. The cost of the technology also dictates that that it is used with genetically superior stock. Superovulation and embryo transfer offers the client an opportunity to increase the number of progeny born from one female from one to above five annually, with repeated superovulatory procedures.  

The art of superovulation in cattle was developed forty years ago, whereby exogenous pregnant mare serum gonadotropin (PMSG) was administered to cows during the middle of their cycle. This induced follicular growth. Removal of endogenous progesterone by administration of prostaglandin induces heat. Multiple ovulations arise from this heat. Seven days after this heat, the embryos are recovered from the uterus. 

In the early development stages of the technique, embryos were recovered either surgically, or by laparoscopy, or by transvaginal insertion of a catheter into the uterus. Further development resulted in a technique involving trans-cervical insertion of a three way catheter into the uterus, uterine lavage using a flush medium to recover the embryos. 

The initial use of PMSG resulted in a superovulatory response, but the half-life of the drug could not be controlled successfully. This resulted in a large variation in embryo development stages and quality. Further issues arose because of luterization of unovulated follicles. 

Administration of purified follicle stimulating hormone on a repeated basis (twice daily) over 4 days during the dioestrous phase of the oestrous cycle results in a more defined superovulatory response. 

Embryos are evaluated under a microscope to assess suitability for direct transfer, to a surrogate female or cryopreservation from subsequent transfer. 

Surrogate females have to be on day 6 to 8 of the oestrous cycle for the purpose of embryo transfer from the superovulated donor cow. 

The art of embryo transfer today involves trans-cervical transfer of the embryo to the ipsilateral horn of the surrogate female. Pregnancy rates from fresh transfer of embryos are similar to conventional AI, whereas pregnancy rates following transfer of frozen-thawed embryos are 5 to 10% lower.