Effect of season on estrous cycle of Yankasa sheep

An investigation was conducted to establish the effects of harmattan and hot-dry season on estrous cycle length, onset, and duration of estrus in Yankasa sheep indigenous to the Nigerian guinea savanna zone. Mean cycle lengths were 16.8 +/- 0.58 and 16.4 +/- 0.53 days during harmattan and hot-dry seasons, respectively; short cycles, 5-13 days, and long cycles, 21 to 30 days, were observed during both seasons. During the harmattan season, 57.1% of estrus began at night while 70% started at night during the hot-dry season. The duration of normal estrus observed during the harmattan, 33.6 +/- 5.87h, significantly decreased (P0.05) during the hot-dry season (24.0 +/- 5.45h). It is suggested that twice daily observation at 12-hour intervals will suffice to detect estrus in this breed of sheep.