Breeding Soundness Evaluation for Stallions

By Heather Smith Thomas

Dr. Ryan Coy, Royal Vista Southwest, Purcell, Oklahoma, specializes in equine reproduction and tells owners that stallions should have a breeding soundness evaluation prior to the breeding season. “Before we focus on collection to see if the stallion has enough sperm cells, we assess the whole horse, including behavior and musculoskeletal soundness. If he is sore in the hocks or the back, for instance, he won’t want to mount a mare or phantom. If there are any soundness issues we can try to get them corrected or under control before breeding season,” he says.

There are several steps involved in evaluating semen. “First we need to collect the horse to clean out his epididymal reserves. The testicles continually produce sperm cells and they are stored in the epididymis until ejaculated. If the sperm cells have been in storage awhile, they deteriorate and are not as viable as younger cells. The longer they are stored, the poorer the semen quality,” explains Coy.

“For this reason, we collect the horse at least 3 times—once a day for 3 days or every other day for 3 days. Multiple collections clear out the old, stored sperm cells before the actual evaluation.”

Twenty-four hours after that third collection the stallion should be collected again for semen evaluation. This will give a better idea about he will be producing during breeding season. “The semen will be evaluated for motility, velocity, total numbers, and any major sperm defects that significantly affect fertility. In a typical breeding soundness exam we collect the stallion, and then an hour later collect him again. The second collection numbers usually drop about half if you’ve cleaned out the epididymis with the previous three collections. This gives an idea what his daily sperm output will be.”

This helps you estimate how many mares the stallion will be able to breed or provide semen for in a day. “This might be 50 mares or 200 mares, depending on fertility of the stallion,” he says.

“After we collect the horse and his testicles are down and scrotum is relaxed, we palpate and measure the testicles. We palpate to determine their consistency and size–whether average, above or below. We check the consistency of the testicles and measure them with ultrasound to determine total mass and make a prediction of potential total sperm production,” Coy explains.

“We palpate both testicles and assess uniformity. Any abnormalities such as drastic disparity of size, a soft or too-hard texture often correlates with poor sperm quality and/or lower than expected sperm numbers. Position of the tail of the epididymis should be noted. Normal position is a caudal orientation (toward the rear of the horse), but it is not uncommon to find a 180-degree rotation with no ill effects, due to a twisted spermatic cord. Semen collections give us an opportunity to evaluate his behavior, and evaluate the penis for normal function and conformation.”

“We culture the semen (to check for potential infection) and process it, just like we were going to ship it. We need to dilute it or extend it and cool some samples so we can evaluate it at 24 and 48 hours (regarding motility, etc.) to see how well his semen ships,” explains Coy.

During or after the breeding soundness exam, if any major issues arise, these can be pursued with further evaluation. “This may require a reproductive specialist who has the training, knowledge and equipment for this,” he says.