In 2003, the horse industry directly contributed $10.7 billion to the U.S. economy; $2.2 billion of that was from the breeding industry alone, according to a study published in 2005. It’s no wonder that Karin Bosh’s July 11 graduate defense seminar at University of Kentucky’s Gluck Equine Research Center–which identified factors such as the mare’s age and stallion book size that affect mare pregnancy and live foal rates–was well attended.

Bosh followed 1,983 Thoroughbred mares from thirteen Central Kentucky farms through the 2004/2005 breeding seasons and the 2005/2006 foaling seasons in an effort to identify common factors associated with mare pregnancy and live foal rates.

Bosh said the basics of mare management boils down to two things: Does the mare get in foal each year, and how many breeding cycles does it take to achieve this? The latter is especially important as top stallions’ books grow larger; limiting the opportunity to cover a mare multiple times.

“In 1992, on average, nine mares were bred to a single stallion, whereas in 2005, 17 mares are being bred to a single stallion,” Bosh said. Kentucky-based stallions breed 58 mares on average during each 150-day season (that equates to covering one mare every two to three days), and that’s only an average. When you look at a horse such as Lion Heart, with a book of 233 mares, there’s very little time for rebreeds