Factors Impacting Stallion Sperm Analysis

A stallion’s fertility can be assessed in part by evaluating both the motility and the shape of the individual sperm cells. Laboratories dedicated to this delicate task often use different staining methods to microscopically evaluate the structure of sperm cells. A recent study, however, shows that staining method and evaluator experience could impact the evaluator’s impression of sample quality, potentially resulting inaccurate evaluations.

“When assessing stallion spermatozoa, laboratory technicians typically consider three main regions of the cells: the tip of the sperm cell that penetrates the mare’s egg, called the acrosome; the main part of the sperm cell or head containing DNA; and the midpiece that connects the head and tail,” said Laura Petroski, B.V.M.S., staff veterinarian for Kentucky Equine Research (KER).

According to the research team, three different staining techniques can be used to assess spermatozoa morphology. Variability in staining technique, in addition to the individual evaluator’s experience or opinion, can introduce errors into the microscopic analysis of semen samples. To test these potential variances, samples were collected from 40 stallions of different ages and breeds. Each sample was subsequently analyzed using three different staining procedures (DiffQuick, eosin-nigrosin, and SpermBlue) and two different evaluators. One evaluator was deemed novice and the other experienced.

Although poor dye fixation was observed with SpermBlue, all three stains were equally useful in identifying morphologically normal spermatozoa. In contrast, the authors noted that “significant differences between evaluators were observed in the classification of some anomalies affecting mainly the midpiece and the tail.” In other words, the novice evaluator misjudged or misclassified certain morphological abnormalities.

“Many factors impact the quality of a stallion’s ejaculate, including season, age, and diet. Certain nutritional supplements also support and possibly enhance stallion fertility, including vitamins A and E and omega-3 fatty acids,” advised Petroski.

She added, “The supplement EO-3 is a rich source of DHA and EPA, and supports sperm concentration, motility, and viability.”

*Murcia-Robayo, R.Y., E. Jouanisson, G. Beauchamp, et al. Effects of staining method and clinician experience on the evaluation of stallion sperm morphology. Animal Reproduction Science. In press.