Covering broodmares during the first month postpartum, often on the first postpartum estrus (termed "foal heat"), is routine practice at many dedicated breeding operations to ensure mares foal at roughly the same time each year. A mare that fails to conceive shortly after foaling continues to have subsequently later foaling dates, eventually missing a breeding season altogether and creating a financial setback for the farm. Generally breeders have a three- to four-week window of opportunity to achieve pregnancy after foaling to still maintain yearly foaling intervals, but a team of researchers recently set out to evaluate the impact of postpartum breeding date on pregnancy rates, pregnancy loss rates, and foaling rates.

Texas A&M University researchers analyzed data for the breeding cycles of 2,003 foaling mares over a three-year time frame at a Kentucky Thoroughbred breeding farm to determine the relation between postpartum breeding day and fertility outcome (producing a live foal). 

“Use of multiple logistic regression (a statistical technique utilizing several explanatory variables) to control for factors influencing fertility outcomes and a fairly large database allowed us to examine influence of each specific day postpartum at breeding,” explained Texas A&M’s Terry Blanchard, DVM, MS, Dipl. ACT. “Looking at each day postpartum is novel, rather than picking an arbitrary cut-point