Male reproductive condition is the limiting factor of efficiency in the male effect during seasonal anestrus in female goats

Two experiments were conducted to determine whether the failure of males to induce sexual activity in goats during seasonal anestrus is due to unrespo nsiveness of females to male stimulus or insufficient stimulation from male s. In the first study, one group of males (sexually inactive, SI; n = 4) wa s kept under natural photoperiod while the other (sexually active, SA; n = 4) was subjected to 2.5 mo of long days (16L:8D) and received 2 s.c. implan ts of melatonin. Two mo later, 2 different flocks of anovulatory goats prev iously separated from bucks were exposed to either SI (n = 34) or SA (n = 4 0) bucks. Progesterone assays and estrous behavior were used to determine o varian and behavioral responses of the females to teasing. Of the goats exp osed to SI males, only 2 ovulated, and none showed estrous behavior during the 35 days of the study. In contrast, all females (40 of 40) in contact wi th SA males ovulated and showed at least one estrous behavior during the fi rst 11 days following male introduction (P < 0.001). Overall, 38 of 40 fema les stimulated with SA bucks were diagnosed pregnant at Day 35, according t o progesterone assay (versus 0 in SI-treated group: P < 0.001). To control for a possible difference of responsiveness between flocks, the experiment was repeated 1 yr later using a single flock of goats divided into 2 groups . Again, over the first 14 days, 1 of 33 goats showed estrous behavior in t he SI-treated group versus 27 of 33 in the SA-treated group (P < 0.001). Th erefore, treating bucks with long days and melatonin increased their teasin g capacity to induce sexual activity in females during anestrus. These resu lts indicate that the absence of response to teasing at this time of the ye ar is not due to female unresponsiveness, but to insufficient stimulation f rom the male.