POSSIBILITIES AND PROBLEMS ASSOCIATED WIT H EMBRYO-TRANSFER IN HORSES.1. REVIEW

There is a substantial lack of knowledge in the Hungarian scientific l iterature on the possibilities of embryo transfer in horses. In these two articles the authors try to highlight this area of research both w ith a thorough review of the literature and with a report of the first successful embryo transfer in mares in Hungary. The review begins wit h a historical introduction of the most important steps in equine embr yo transfer then it is followed by a systematic description of the tec hnique. Emphasis should be put on the proper selection of both the don or and recipient mares. Recipients should be of 3 to 10 years of age w ith moderate condition and good fertility. The success of the transfer is depend on the synchrony between the donors and recipients. Recipie nt should ovulate either 1 day before or 3 days after the donors. In c ase of limited number of recipients the synchronisation can be carried out using progestins, PGR, and HCG. The flushings can be done on day 6-8 after ovulation using the so called gravitation technique with 1-3 litres of DPBS containing 1% fetal calf serum. The average recovery r ate is approximately 60-80% but major differences may occur depending on the reproductive background of the donors, the semen quality and th e time of flushings (day 6-day 8). Embryos are recovered either as mor ula (day 6, 150-200 mu m) or blastocyst (day 7-8, early, expanding, 40 0-800 mu m) and are morphologically scored on the 1 to 5 scale (1 exce llent, 5 degenerated). Transfers should be performed as soon as possib le after recovery either surgically or non surgically. In case of the surgical technique midline or flank approach can be used resulting in higher pregnancy rate than the non surgical way. The difference betwee n the two technique maybe the result of local inflammation and PGF(2 a lpha)-release owing to cervical dilation during the manipulation. Ther e is also intensive research on different methods to improve the effic iency of equine embryo transfer. Crude equine gonadotrophin can be use d for superovulation which result in elevated ovulation rate but has a negative effect on the recovery rate. The freezing of equine embryos can also be done successfully but large scale practical application ha s not been achieved yet.