Evaluating Semen Quality
Keep all equipment used in semen evaluation at 37°C and free of any spermicidal agents. Evaluate each ejaculate to assure the maximum number of normal, progressively motile spermatozoa. The following criteria are used to determine semen quality, total sperm output and insemination dose: volume, concentration, motility and morphology.
Volume is simply the total amount of gel-free semen in a single ejaculate and is usually measured in milliliters.
Concentration is determined by using a hemocytometer or spectrophotometer. Concentration is important because it influences total sperm output and insemination dose if artificially inseminating. Most stallions will ejaculate approximately 7 billion spermatozoa.
Motility should be determined as soon after collection as possible. To do so, put a drop of semen on a warm slide, covering it with a warm cover slip and estimating the percent of normal progressively motile spermatozoa using a microscope. Progressively motile spermatozoa is defined as those sperm cells that are swimming straight across the microscope screen and having normal morphology. Sixty percent progressively motile spermatozoa is considered good; anything below 60% is questionable.
Sperm morphology can be determined by microscopic evaluation of stained smears or, preferably, phase-contrast microscopy. Note any abnormalities such as bent tails, no heads, no tails, macrocephalus, double heads and immature sperm cells and record the number. Total sperm output is determined by multiplying volume and concentration. Calculate the total number of progressively motile spermatozoa by multiplying total sperm output by the percentage of progressively motile sperm cells. If artificially inseminating, mares should be inseminated with 500 million normal progressively motile sperm cells. All these characteristics combine to determine the quality of a stallion’s semen. Evaluating a stallion as a potential breeder encompasses many aspects of his conformation and anatomy. As stallion owners or potential owners, we must be critical of the stallions we use for breeding, taking into account their physical conformation, reproductive anatomy and semen quality so that we continue to introduce and produce the highest quality horses. All of the examinations and parts mentioned may not be used or examined by the person conducting the examination. This article provides information for the type of exams that could be conducted. The situation and circumstances of the purchase will dictate which ones you actually use.
Kathy Anderson, Extension Horse Specialist, University of Nebraska