Preliminary results of a collaborative effort between researchers at Oklahoma State University and Texas A&M University were recently presented at the American Association of Veterinary Laboratory Diagnosticians in San Diego, Calif. These researchers compared antibiotic properties of common equine semen extenders with four different strains of bacteria, including Taylorella equigenitalis, the causative organism for contagious equine metritis (CEM).

Unique to this study were the comparisons of how these extenders and bacteria affect semen quality and longevity.

Equine semen that is packaged and cool-shipped for artificial insemination (AI) is almost always extended with a skim milk- or egg yolk-based semen extender. There are multiple types of these extenders available on the market, but results on their benefits and detriments are not definitive.

In equids, they are utilized for their ability to maintain plasma membrane integrity while protecting spermatozoa from cold shock, detrimental seminal plasma proteins, and toxic byproducts produced by the sperm cells. Most extenders used today also contain antibiotics to decrease bacterial growth in semen; however, additional antimicrobial supplementation of extender is also accepted