The influence of mare numbers, ejaculation frequency and month on the fertility of Thoroughbred stallions

Abstract

This survey has identified wide differences between the per mating pregnancy rate in TB stallions. Identification of the factors involved through more comprehensive surveys would provide useful information for mare and stallion owners.

Key Factors Affecting Reproductive Success of Thoroughbred Mares and Stallions on a Commercial Stud Farm

“…Work conducted by Sanderson and Allen () reported only 3.3% of all coverings in February. More recent studies report higher frequency of coverings in February; almost 12% of coverings in this study occurred in February, similar to recent UK data (10%; Allen and Wilsher ) and USA data (14%; Bosh et al. ).…”

“…Only 6.5% of all coverings were categorized as high usage where a stallion had been used for more than 21 coverings in the week preceding the mating in question. Unlike the UK study (Allen and Wilsher ), per cycle pregnancy rates were lowered (p < 0.01) where stallions were classified as overused: 60% for coverings using high usage stallions compared with 68% for coverings with normal usage stallions. There was no effect of individual stallion, age of stallion, time (year or month of cover), shuttling, and usage per day on pregnancy rate or pregnancy loss rate after accounting for all factors and interactions.…”

“…Blanchard et al. () and Allen and Wilsher () demonstrated an effect of month with mares covered later in the season experiencing lowered pregnancy rates; although numerically lower in this study, it was not significant using logistic regression modelling.…”

“…), month of breeding (Blanchard et al. ; Allen and Wilsher ) and breeding at foal heat (Blanchard et al. ) contribute to reproductive success.…”

The 50 year veterinary revolution in equine stud management

“…This increase, combined with the common practise of "shuttling" stallions between the northern and southern hemispheres, means that some horses now cover 300 or more mares in a calendar year. This is an incredible number when considering that the stallion, if "living in the wild", would impregnate a harem of only some 5-15 mares annually and it is surprising that relatively few Thoroughbred stallions show definite signs of reduced fertility as a result of overuse (Bosh et al 2009, Allen andWilsher 2011).…”