Breeding Cents

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.

"Due to the increasing demand for the stallions, it is more difficult to schedule multiple breedings during the season," Bosh said. "Therefore, it is important to improve the efficiency in which we are getting the mares in foal."

To help them better understand how to do so, Bosh identified factors using studying data provided by the farms that directly affected the mare's pregnancy and live foal rates.

One major factor commonly affecting pregnancy, pregnancy loss, and live foal rates in both years was the mare's age. Bosh explained that as the age of the mare increased, the difficulty of getting that mare in foal and maintaining pregnancy also increases.

"Older mares are less effective at getting in foal, and less effective maintaining pregnancy," Bosh explained. The average live foal rate for study horses was 79%; however, live foal rates for mares over the age of 18 was 43.4%.

Large stallion book size, Regumate, (oral)/progesterone (IM) administration, and ovulation inducing drugs (hCG or Ovuplant) were positive factors affecting pregnancy rates 15 days post-breeding.

Pregnancy loss between Days 15 and 40 was related to the mare's age and status. It was generally the mares with suspected problems, as evidenced by administration of Trental.

Other factors that were associated with a higher live foal rate included the number of foals produced by the mare without a break and a foaling date prior to April 1. Factors related to a lower live foal rate included the number of times the mare was breed during the season and age of the mare.

Bosh explained, "By understanding the factors that affect reproductive efficiency, especially those that can easily be changed, you have the possibility of improving pregnancy overall."

About the Author

Chad Mendell

Chad Mendell is the former Managing Editor for .

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