SEASONALITY OF ESTRUS AND OVULATION IS NOT MODIFIED BY SUBJECTING FEMALE ALPINE GOATS TO A TROPICAL PHOTOPERIOD

In order to determine whether seasonality of estrus and ovulatory activities was maintained in Alpine goats, when subjected to tropical photoperiodic variations, two groups of 9-month-old females (n = 13 each) were used. After October, one group was kept for 33 consecutive months under a yearly photoperiodic cycle which simulated a temperate photoperiodic cycle (TE: 8 to 16 h of light per day) and the other group was kept under a tropical photoperiod (TR: 11 to 13 h of light per day) for the same duration. Estrus was monitored twice daily and ovulatory activity determined twice weekly by blood progesterone assays; during the last breeding season, ovulation rate was assessed at each cycle by laparoscopy. Seasonality of estrus and ovulatory activities appeared in both groups; the seasonal anestrus occurred during the same period under the TE and TR photoperiodic cycles (February to September for anestrus and March to September for anovulations). Females exposed to the TR photoperiodic cycle began their breeding season significantly earlier and with more variability than those exposed to the TE photoperiodic cycle, especially during the second season (37 and 17 days earlier for estrus and ovulations, respectively). The difference was attenuated at the beginning of the third season. The second breeding season was of significantly longer duration in group TR than in TE (49 and 31 days longer for estrus and ovulations, respectively). Duration of the third breeding season was not significantly different between groups. Durations of estrous behavior and ovulation rate were not different between groups. Estrus without associated ovulation and estrous cycles of short duration ( < 17 days) appeared more frequently in group TR than in group TE, during the second, but not during the third season. It was concluded that seasonality in estrus and ovulatory activities of Alpine goats was not modified when females were exposed to a simulated tropical photoperiod.