Not all stallions are created equal and neither is the amount of sperm they produce. The most sought-after stud in the area, for instance, could produce minimal amounts of semen, while a less desirable horse might produce more than his breeders ever need. So what are the deciding factors when it comes to sperm production?

Ed Squires, MS, PhD, Dipl. ACT (hon.), reviewed some of those factors at the 2015 World Equine Veterinary Association Congress, held Oct. 8-10 in Guadalajara, Mexico. Squires is a professor at the University of Kentucky’s Gluck Equine Research Center, in Lexington.

“It is important for both veterinarians and stallion managers to know the factors that affect sperm output in stallions,” Squires said.

Those key factors include stallion age, season, testis size, ejaculation frequency, and sex drive