With breeding season fast approaching, stallions should undergo breeding soundness exams before starting to breed mares, whether via artificial insemination or live cover.

Because overall health is critical to a stallion's reproductive success, a stallion must be in good physical condition and not overweight at the start of the season. Stallions carrying too much extra weight might show decreased sperm quality. Like all horses, they need exercise to maintain mental sharpness and a healthy body condition.

"It's not good for the stallion to be fat," said Ed Squires, PhD, Dipl. ACT (hon.), director of University of Kentucky (UK) Ag Equine Programs and executive director of the UK Gluck Equine Research Foundation. "The problem ... is that fat in the scrotum insulates the testicles, which increases the temperature which, in turn, affects sperm production and quality."

Squires points out that in the Thoroughbred industry, stallions are rarely fat. They generally are turned out in a paddock, able to exercise freely, or they are in a sophisticated exercise program. But in the show horse industry, more stallions are overweight. Part of this is management: The non-Thoroughbred world doesn't always have access to the same type of housing and turnout as the Thoroughbred world; they rely on alternatives such as hot walkers and hand walking.

For an artificial insemination program, semen should be collected several days in a row to stabilize sperm output collection. Then a reproductive specialist should conduct a breeding soundness exam on the horse.

"It's important to look at semen, usually by January, to assess the horse's semen parameters going into the breeding season," Squires recommended. "Breeding soundness is an indication of where the horse is in terms of quality and sperm production, and those factors will determine how many mares he can handle. Additionally, once the stallion reaches his 'teenage' years, it's important to check sperm regularly so you have a baseline for his sperm count and quality in case changes occur dramatically."

A breeding soundness exam measures:

Motility. Progressive motility, or sperm "quality"--an important parameter--measures how many sperm move in a straight line across a field. Owners should look for a range of 60 to 70% of the sperm being progressively motile with below 50% being a problem.

Total number of sperm in the ejaculate. This will vary according to testicle size, season, and age of the horse. Look for sperm count in the 10 to 20 billion per ejaculate range. For a breeding evaluation, two collections can be taken one hour apart. There should be half the sperm in the second ejaculate as in the first.

Testicle size. Testicles can be measured either with ultrasound to measure volume or plastic calipers to measure width. This should be done several times a year to measure relative changes in size.

Bacterial shedding. A horse can be physically healthy and still shed bacteria, so take swabs from the urethra, semen, and prepuce for bacterial cultures.

Morphology. Generally more than 50% of the sperm should be morphologically normal.

According to Squires, a breeding soundness exam before the season begins helps owners determine how many mares the stallion can likely handle. It will answer the following questions:

  • Is the stallion fit, not fat?
  • Has he changed from the previous year?
  • Is his semen healthy in terms of sperm count morphology and motility?

Karin Pekarchik is an editorial officer in UK's Agricultural Communications Services.


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More information on Gluck Equine Research Center and UK's Equine Initiative.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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