A NEW METHOD FOR CONTROLLING THE PRECISE TIME OF OCCURRENCE OF THE PREOVULATORY GONADOTROPIN SURGE IN SUPEROVULATED GOATS

In goats treated to induce superovulation, insemination at a predeterm ined time after the end of progestagen treatment leads to a low fertil ization rate. To solve this problem we developed a new treatment based on the control of the occurrence of the endogenous LH peak with a GnR H antagonist (Antarelix (R)). The first experiment was designed to det ermine the dose of LH required to mimic a spontaneous LH preovulatory discharge; the injection of 3 mg, i.v. of pLH induced a peak of the sa me amplitude and duration as the spontaneous peak. Subsequently, in th e second experiment, we compared 2 doses of Antarelix (R) (0.5 and 1 m g, sc) administered 12 h after sponge removal (9 goats/treatment group ). The dose of 0.5 mg was selected for further experiments because it was effective in the inhibition of the endogenous LH peak and had no d etrimental effect on the quality of embryos. In the final experiment, 48 goats received the new treatment and were inseminated (intrauterine ) only once 16 h after LH injection; 41 were flushed and produced 5.3 +/- 4.5 (m +/- SD) transferable embryos. The developmental stage and t he number of cells/embryo were within the range that has been reported for embryos produced with conventional treatments. In conclusion, wit h the described method, it is possible to inseminate goats at a predet ermined time without decreasing the number of transferable embryos. Th is technique will encourage the development of embryo transfer within genetic programs, and it will be a valuable tool for the production of zygotes for gene transfer.