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Abstract
John Brinkerhoff

Fellow – John Brinkerhoff

Mentor – Charles Love

Project – Influence of mare age, pre-breeding mare status, breeding method, and stallion fertility on first cycle pregnancy rates within a commercial situation

Objective – The relationship between stallion (sperm quality), mare (age and pre-breeding status), and management (fresh semen, embryo transfer, and cooled/shipped semen) factors has not been studied. Most studies are limited by a small mare population and a single evaluation of the male to represent seasonal fertility; however, this study utilized a large mare population and all ejaculates (n=845) from commercial breeding stallions.

Animals or Sample Population – Privately owned mares (n=1203) were bred to commercial breeding stallions (n=18) standing during the 2008 breeding season.

Procedure – Stallion factors included fresh and extended semen cooled for 24 hours evaluated for motility, morphology, and DNA quality. Mare factors included age and pre-breeding status (maiden, foaling, barren, unknown). Management factors included the method of breeding. The method of odds ratio was used to test the binomial nature (pregnant vs. non-pregnant) of each recorded parameter, and used to determine the degree that each variable contributed to fertility.

Results – Mare age and breeding method were the only two factors that affected the fertility odds ratio outcome. When sperm quality parameters were added to the initial model, all odds ratios included 1.

Conclusions and Clinical Relevance – The results suggest that when fertile stallions are bred by experienced personnel, mare age and breeding method are critical fertility modulators, regardless of the pre-breeding status of the mare. Mare age and breeding method should be considered primary factors when reduced fertility is encountered in the face of normal sperm quality.