By Dr. Juan C. Samper, DVM, PHD, DIPL. ACT
Q: I can only feel one testicle on my yearling stud colt. Is it possible his other testicle could descend later or could he be a cryptorchid? If he is a cryptorchid, will he still be suitable for breeding?
A: If the colt was born with two testicles, chances are that the second one will descend. Colts can drop their testicles with no detrimental effects to their testicular development until the age of two, when they go through puberty. If the testicle is retained after that, then chances are that that testicle will be smaller even if dropped.
It is important to determine where the testicle is. If it is in the inguinal area, there is a high possibility that it will drop, but if it is in the abdomen, it will almost always be retained, so a careful examination is critical.
Males of any species only need one testicle to be able to get females pregnant. Stallions are no different, but cryptorchidism (having one or both testicles undescended) is considered a heritable and undesirable trait, and therefore many organizations and breed registries will not accept a stallion that does not have two descended testicles of similar size for breeding. Cryptorchids are also known to be tougher to handle than normal stallions and certainly more difficult than geldings.
Dr. Juan Samper, MSc, PhD, Diplomat ACT, operated JCS Veterinary Reproductive Services in Langley, BC, from 1993-2017. He has consulted with breeders and veterinarians in over 25 countries. He served as the Associate Dean Clinical Affairs at Ross University School of Veterinary Medicine from 2014 to 2017, and is presently the Associate Dean of Students and the University of Florida College of Veterinary Medicine.
This article was originally published in the April 2011 issue of Canadian Horse Journal.