SYNCHRONIZATION OF ESTRUS IN GOATS - THE RELATIONSHIP BETWEEN ECG BINDING IN PLASMA TIME OF OCCURRENCE OF ESTRUS AND FERTILITY FOLLOWING ARTIFICIAL-INSEMINATION

Radioimmunoassay (RIA) was used to measure plasma eCG binding in dairy goats (n=524) at the beginning of a progestagen/eCG treatment and 25 d after eCG administration. The eCG binding was not dependent on the a ge of the females but increased with the number of treatments they had previously received (3.4 % +/- 4.8, n = 47 vs 9.6 % +/- 13.2, n = 249 ; mean +/- SD; P < 0.01 for goats treated 0 and 1 time vs those treate d 2 to 5 times, respectively). The synchronization treatment led to an increase in the binding of eCG (7.1 % +/- 10.9 before vs 28.3 +/- 24. 5 after treatment; P < 0.01). When eCG binding before treatment was hi gher than 5 % the onset of estrus was delayed : 37.9 % of goats came i nto estrus more than 30 h after sponge removal vs 7.4 % when eCG bindi ng was lower than 5 % (P < 0.01). Fertility was significantly decrease d when eCG binding was higher than 10 %. These results show that the r epetition of treatment with eCG to induce estrus in goats increases eC G binding. This could explain the lowered efficiency of the hormonal t reatment to synchronize estrus and the associated decrease in fertilit y when goats are inseminated at a predetermined time.