Characteristics of the estrous cycle of the swamp buffalo under temperate conditions.

Estrous cycle, duration of estrus and time of ovulation of eight cyclic buffaloes were examined during a period of one year. Animals were kept under loose-housing conditions and fed according to the Japanese Feeding Standards for dairy cattle. All the animals were observed for the occurrence of estrus twice daily by using a vasectomized bull, and ovarian cycles of each animal were monitored by weekly rectal palpation. Duration of estrus and time of ovulation were determined in 32 estrous periods from eight animals. Animals came in estrus throughout the year. The estrous cycles corresponding to single ovarian cycles ranged from 11 to 38 days with a mode interval of 20 days, averaged 21.5+/-4.7 days. Percentage of the cycles within a range of a mean+/-1 SD (17-26 days) was 79.2%, whereas that of cycles shorter or longer than the expected range was 9.4% and 11.4%, respectively. Estrus took place regardless of the time of day and lasted 9 to 27 hr (19.9+/-4.4 hr). Ovulation occurred 6 to 21 hr (13.9+/-3.4 hr) after the end of estrus, with a mode interval of 12 hr. There were no significant seasonal variations in the estrus characteristics studied.