Abstract
The present study addresses a comparison of various estrous cycle control protocols and the effect of season in the northern temperate zone on the superovulatory response in Boer goats. Four groups of 12 does each were treated in February, May, August and November, respectively. Does were provided with progestogen containing intravaginal pessaries to synchronize estrus. Half the does of each group received sponges impregnated with 20 mg fluorogestone acetate (“Cronolone”), the other half “Eazy-Breed” CIDRs containing 0.3 mg progesterone. Pessaries remained in place for 7 days. Within each subgroup half the does were treated with PGF2α (“Dinoprost”) at pessary insertion, the other half at pessary withdrawal. Beginning 48 h before pessaries were removed does received i.m. injections of 4, 4, 2, 2, 2 and 2 Armour Units (AU) FSH, supplemented with 40% LH, at 12 h intervals. Estrus detection was conducted at 8 h intervals and ovarian activity was monitored by daily transrectal ultrasonography. Does were mated and 7 days later non-surgical embryo collection was conducted. It transpired that the type of intravaginal pessary had no effect on the time passing between pessary withdrawal and onset of estrus (sponge: 40.7 h vs. CIDR: 35.2 h), number of ovulations/doe assessed by echographic counting of collapsed large follicles (7.2 vs. 7.6) or corpora lutea (7.1 vs. 9.8), embryo recovery rate (39% vs. 41%) and proportion of transferable embryos (66% vs. 65%). The number of collapsed large follicles was significantly higher than that of corpora lutea on the day before embryo collection (7.4 vs. 8.5; P < 0.05), the correlation between the two being r = 0.55 (P < 0.05). The effect of PGF2α administration at the onset or at the end of progestogen treatment and the effect of season were not significant, except for a shorter interval between pessary removal and onset of estrus in August in comparison to the other months (29.3 vs. 39.4, 40.6 and 42.1 h; P < 0.05). In conclusion, Boer goats, although being seasonal breeders in the northern temperate zone, will respond to superovulatory treatment and produce embryos of high quality year round regardless of type of pessary and time of PGF2α administration.
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