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Frequent Breeding of Stallions Does Not Affect Live Foal RateBy Kentucky Equine Research Staff · September 23, 2011
Much concern has been expressed among horse industry professionals during the last decade that large books of stallions reduce live foal rate through too frequent breeding.
Researchers at the University of Kentucky set out to establish factors, including book size, that affect live foal rates of Thoroughbred stallions in Kentucky. The researchers chose to use stallions in a tight geographic region to limit the effects of various environmental and management differences.
Thoroughbred stallions standing in Kentucky over a four-year period (2006-2009) were placed in one of four groups according to book size: small (11-50 mares/year), medium (50-100 mares/year), large (100-150 mares/year), and very large (more than 150 mares/year). Stallions with less than 10 mares/year were not included in the study. Age of stallion, stud fee, and farm size were collected for each stallion to determine if these factors were related to live foal rates.
To establish the relationship between stud fee and live foal rate, stallions in 2007, 2008, and 2009 were separated into four groups: stud fees less than $10,000, $10,000-$49,000, $50,000-$99,999, and $100,000 or more. To assess the effect of farm size, data from 2007, 2008, and 2009 farms were divided into three groups: farms with less than five stallions, farms with five to nine stallions, and farms with 10 or more stallions.
Researchers concluded that large book sizes do not negatively influence live foal rates for Thoroughbred stallions standing in Kentucky. From the data collected for this study, it seems stallions in greater demand have increased live foal rates compared to those with smaller books (11-50 mares/year). This refutes the common belief that large books decrease live foal rates. Also, stallions residing on farms with 10 or more stallions had greater live foal rates than those standing at farms with fewer stallions.
This study was presented at the 2011 Equine Science Society Symposium in Murfreesboro, Tenn. The proceedings from this symposium are available from the Journal of Equine Veterinary Science.
