Once a mare produces a top-performance foal, her value as a broodmare greatly increases. And if other of her foals also perform well, she is much-prized. If you use a mare in performance events, she may be 8-10 years old before having foals old enough to perform. So owners want older, proven broodmares. And that's the catch.
Older mares are less likely to have foals.
Data indicate that once mares become 16 years old, they're less likely to have a foal than younger mares. That's frustrating when your breeding program is based on promoting offspring of proven mares. Once mares have two or more proven offspring, they're usually in their early to mid-teen years. In other words, they're close to 16 years old and face and a reduction in their reproductive ability. At day 12, researchers used ultrasound to detect viable embryos in recipients.