Sperm Abnormalities
Teratospermia
Basic Information 
Clinical Presentation
History, Chief Complaint
• Most stallions present with a reduction in fertility or complete infertility. These stallions often were previously fertile and have either acutely or gradually failed to achieve pregnancies. A complete review of the stallion’s breeding records is helpful in determining when the problem or initial insult occurred.
• Some stallions have perpetual infertility. These stallions are usually affected by low sperm quality and increased teratospermia that may have begun at puberty.
Etiology And Pathophysiology
• Genetic factors: The exact genetic factors that lead to teratospermia are not well defined and may overlap with environmental factors.
• Environmental factors: These are the most common causes and result from an insult to the testicle disrupting spermatogenesis. Environmental factors may be any of the following:
• Aging: As stallions age, the efficiency of spermatogenesis may decrease. Older stallions often have a higher number of abnormally shaped sperm.
Diagnosis 
Differential Diagnosis
• Elevated scrotal temperature (pyrexia, elevated ambient temperature, scrotal inflammation, scrotal insulation)
• Incomplete testicular descent (partial cryptorchid, “high flanker”)
• Spermiostasis (plugged ampullae) (see “Ejaculatory Dysfunction” and “Sperm Abnormalities: Azoospermia” in this section)
Initial Database
• CBC and serum chemistry may be beneficial in assessing the stallion for systemic disease or inflammation that may be affecting the scrotal temperature. If orchitis is present, the stallion may exhibit leukocytosis and hyperfibrinogenemia.
• A complete semen evaluation is critical in any case of reduced fertility. A morphologic analysis should be performed every time a fertility problem is diagnosed. The morphology of the sperm is less often affected by artifactual changes (examiner mishandling) than is sperm motility. Morphology should be performed using oil immersion and a good-quality microscope. If using a wet mount, the cells should be examined by phase contrast or differential interference contrast (DIC) microscopy. In practice, most veterinarians will use eosin-nigrosin stain. The stain can also be used to determine the viability of the sperm cells. A normal, viable cell will stain as a white sperm cell on a dark background. If the membrane of the sperm is damaged, the stain will penetrate the cell, causing the spermatozoal head to appear pink.
• All defects—such as abnormal heads, abnormal acrosomes, abnormal midpieces, proximal and distal cytoplasmic droplets, detached or tailless heads, tail defects, and premature germ cells—should be recorded. One hundred cells should be counted and the specific type of defect present recorded. If multiple defects are present on the same sperm cell, they should be counted simultaneously. This gives the examiner a more accurate representation of the frequency of the specific abnormalities present.
• Ultrasound of the testicles should be performed to evaluate the parenchyma for abnormalities such as neoplasia or hyperechoic or hypoechoic areas.
• If defects indicating a problem with transport during ejaculation are present (detached heads, bent tails), palpation and ultrasound of the accessory sex glands should be performed.
• Hormonal assay: Levels of hormones will vary considerably in normal and subfertile stallions; therefore hormonal analysis may be of little value for diagnosis. With severe cases of testicular degeneration, levels of follicle-stimulating hormone and luteinizing hormone may be elevated and estradiol may be low. Elevated levels of exogenous androgens will lead to a disruption of spermatogenesis. If no other specific causes for teratospermia are found, a hormonal assay should be performed.
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