IN-DEPTH INTERACTIVE: REPRODUCTIVE DISORDERS – PATHOLOGY TO TREATMENT


permanent, as is the case with age-related testicular degeneration, where reduced spermatogenic effi- ciency is an early change in the progression of the disorder.34 It is can be coincident with a reduction in the percentages of morphologically normal and progressively motile sperm. Total sperm number is determined as the product


of gel-free semen volume and sperm concentration. To maximize sperm contained in the gel-free semen, semen should be collected in a receptacle that is fitted with a nylon-micromesh filter, as this type of filter will effectively separate gel from gel-free se- men, and will reduce loss of sperm within the filter. The most accurate method of estimating semen vol- ume is by weight (1 g  1 mL). Sperm concentra- tion is typically determined with a hemacytometer counting chamber, spectrophotometrically, or with a semiautomated fluorescence-based sperm counter. Reduced sperm motility can imply a reduction in


the percentage of motile sperm, the percentage of progressively motile sperm, or the average sperm velocity. For objectivity, this analysis is best per- formed using a computerized sperm motility ana- lyzer. If unavailable, a phase-contrast microscope equipped with a warming stage can be used for subjective analysis, with the magnification set at 200–400. For most accurate assessment of pro- gressive motility, the sample should be diluted with extender sufficiently (i.e., to 30  106 sperm/mL) so that one can more critically assess motion charac- teristics of individual sperm. As an adjunct to as- sessment of sperm motility, examination of sperm membrane intactness (a measure of sperm viability) can yield valuable information regarding sperm function.35,36 One study revealed that sperm “via- bility” may be a more accurate predictor of the fer- tility of cool-stored semen than sperm motility.37 Automated analysis of equine sperm morphology


is unreliable, in the author’s experience, but vivid images of sperm can be viewed using differential interference contrast microscopy at magnification of 1000–1500. Such specimens are examined as a wet mount after fixation of sperm in buffered formol saline.38 Phase contrast microscopy can be used if differential interference contrast optics are unavail- able. The authors consider either method to be superior to microscopic examination of stained dry- mounted specimens. A minimum of 100 sperm are evaluated, and the incidence of each type of morpho- logic defect is recorded. The sperm defects that are the most significant predictors of fertility are normal sperm (positively correlated with fertility) and ab- normally shaped heads, detached heads, general mid-piece abnormalities, coiled tails, and premature germ cells (negatively correlated with fertility).39 The etiology of oligospermia, necrozoospermia,


and/or teratozoospermia is variable. Testicular dysfunction is a leading cause of these clinical find- ings. Although testicular dysfunction can be ge- netic, environmental causes are possible and include those associated with various medications and con-


260 2015  Vol. 61  AAEP PROCEEDINGS


ditions that cause an increase in scrotal tempera- ture (including an increase in body temperature). Age-related testicular dysfunction also results in a progression of reproductive changes, beginning with a reduction in spermatogenic efficiency and the number of morphologically normal, progressively motile sperm in ejaculates. These clinical changes generally occur prior to a marked decline in testic- ular volume in association with age-related testicu- lar dysfunction.34 One relatively common cause of oligospermia, necrozoospermia, and teratozoospermia is a condi- tion called spermiostasis, or plugged ampullae. These stallions are sometimes referred to as sperm accumulators. With this pathologic state, sperm tend to accumulate in the extragonadal ducts, pri- marily in the ductus deferens and glandular ampul- lae in the terminal segments of the ductus deferens. The condition occurs following extended periods of sexual abstinence, and can affect sexually mature stallions of any age. Stallions with the condition are more likely than the general stallion population to have issues with recurrence. Although spermiostasis can result in necrozoospermia and teratozoosper- mia, in the presence of extraordinarily high sperm output, ductal blockage oftentimes results in con- current oligospermia, or occasionally, azoosper- mia (no sperm in ejaculates). A pathognomonic finding of severe cases is a high percentage of detached heads (tailless heads) in the ejaculate. High percentages of hairpin bent tails and/or distal protoplasmic droplets are oftentimes indicative of stagnant sperm in the extragonadal ducts and repre- sent a propensity for more pronounced clinical signs such as oligospermia, a high incidence of detached heads, or even complete ductal blockage if the stallion is not subjected to increased breeding frequency. Diagnosis is based on assessment of the ejaculate, in combination with transrectal palpation/ultrasono- graphic evaluation of the ampullar regions.40–42 Degenerating sperm may be ejaculated in numerous clumps (or casts). These can be missed if an in-line gel filter is discarded before its contents are exam- ined. Palpation per rectum may reveal enlarged, turgid ampullae. Ultrasonographic examination will oftentimes disclose dilated ampullar luminae. The diameter of the ampullae in reproductively nor- mal stallions is quite variable (16.3  3.6 mm) and the lumen can contain a small amount of echolucent fluid.43 The luminal diameter can increase fol- lowing sexual stimulation,44 but dilated ampullar luminae in a nonsexually stimulated stallion are highly suggestive of spermiostasis involving the ampullar regions. Sperm-occluded ampullae are occasionally associated with cystic remnants of the Mu


¨ llerian ducts, which can be visualized ul-


trasonographically at the terminations of the am- pullae within the colliculus seminalis.45 Treatment strategies for reduced semen quality


are dependent on the underlying causes and the rules and regulations of the breed registry involved.


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