Studies of fertility in the thoroughbred mare. 2. Early post-partum oestrus (“foal heat”).

This article explores the phenomenon of early post-partum estrus (also known as “foal heat”) in thoroughbred mares compared to other domesticated animals like bovines, sows, and ewes. The study also provides evidence of successful conception rates when mares are mated during this period.

Post-Partum Estrus in Other Animals

• The research highlights the uniqueness of early post-partum estrus in equidae and bactrian camels among domesticated animals.
• For instance, cows generally undergo the first heat after calving over a variable longer period, usually over 40 days.
• Meanwhile, sows and ewes typically do not experience heat during lactation. In the case of sows, heat generally follows a week after the young have been weaned.
• The study further notes the occurrence of post-parturation heat in other species such as certain rodents, marsupials, and seals, emphasizing the unknown factors determining the presence or absence of this phenomenon within different species.

Early Post-Partum Estrus in Thoroughbred Mares

• In a thoroughbred mare specific study that observed 1,366 estrus cycles, heat after foaling is noted to occur between the 4th and the 17th day in equine species.
• The research illustrates that in 90 percent of the cases, this foal heat appeared between the 7th and 11th day post-partum, with the ninth day standing as the average onset day.
• Notably, the mating of mares was successful in just over half the cases, specifically between the 11th and 14th day after foaling.
• Other studies referenced indicate varying conception rates when mares were mated on different days post-partum, demonstrating the critical significance of precise timing for successful conception.
• The article finalizes the insight by presenting data from Trum’s study (1950) indicating the appearance of foal heat in 93 percent of mares within 5 to 18 days after foaling, showing varying frequencies depending on the exact day post-partum.