INDUCTION OF ESTRUS IN SAANEN GOATS AT EARLY BREEDING-SEASON BY INTRAVAGINAL PROGESTERONE SPONGES (MAP) OR BY PROSTAGLANDIN-F-2-ALPHA INJECTIONS - EFFECT ON DIFFERENT AGE-GROUPS

Twenty-one maiden and 20 pluriparous milking Ankara Saanen goats received either two i.m. injections of PGF2.alpha. (n = 25) or intravaginal MAP sponges (n = 25) early in November at the start of the breeding season. About twice as many pluriparous goats as maiden goats exhibited estrus after either treatment (87% vs. 47%). Breeding after this induced estrus caused pregnancies in 62% of the pluriparous goats, but only in 24% of the maiden animals. Maximal concentrations of progesterone were reached 11 days after the start of the MAP treatment. Progesterone declined to basal levels two to four days after sponge withdrawal. A significant slower progesterone increase also resulting in lower maximal concentrations could be observed in maiden goats. Luteolysis was evident in all animals within 24 h after PGF2.alpha. injection. Nine goats (six maiden and three pluriparous) did not exhibit heat after the second injection and showed only a slow increase of progesterone. It seems that noncyclic animals are less sensitive to MAP treatment than to the first PGF2.alpha. injection. Goats at the beginning of the breeding season may react after a premature interruption of corpus luteum function (after second PGF2.alpha. injection) with delayed or inadequate follicular function.