An experiment was carried out at Bahia Blanca (38°44' S, 62°10' W) to estimate the seasonal variation in ovulation rate and its components shown by Lincoln ewes of constant live weight.
Twenty-three 5-year-old ewes were subjected to nine 17-day observation periods which were evenly spaced within 405 days.
Percentage of ewes showing oestrus and ovulation, incidence of multiple ovulations and ovulation rate were estimated for each period by using vasectomized rams and performing iaparoscopies.
Traits showed a similar seasonality which was presumably induced by the natural light regime to which the ewes became exposed before and during each observation period.
A significant and periodic relationship was found between each trait and the number of days elapsed from the longest day.
The predicted maximum values for each parameter were reached about 40 days before the shortest day. Prior to and after this date both the percentage of ewes showing oestrus and ovulation and the incidence of multiple ovulations declined so that the expected ovulation rate values became zero for a period of about 3 months before the longest day.