Five hundred and forty nine foaling thoroughbred mares, were observed to analyze the conception rate, duration and fertility of the foal heat, foaling rate in the forthcoming year and its relation with the age of the mare during the 2nd semester comprised between July, 1983 and December, 1994. Conception and foaling rates decreased after the age of the 13th. The first estrus appeared 12.3 (± 10.9) days post-partum and, when its duration was between 8 and 14 days, the first estrus was significantly more fertile than out of these limits. The conception rate of the second post-partum estrus was significantly higher than the first.
Mare; Post-partum estrus; Fertility; Age
