Sperm Abnormalities
Azoospermia
Basic Information 
Clinical Presentation
Disease Forms/Subtypes
• Nonobstructive azoospermia: Occurs when there is a problem with spermatogenesis such as with testicular hypoplasia or degeneration.
• Obstructive oligozoospermia: Occurs when spermatogenesis is normal but sperm cannot be ejaculated because of a physical blockage anywhere between the testicle and the urethra.
History, Chief Complaint
• A complete absence of spermatozoa in the ejaculate, infertility.
• A complete breeding history aids the examiner in narrowing down the differential list. Often, the owners will have records of previous ejaculates, mare records, and seasonal or per cycle pregnancy rate. Stallions may present for acute onset or gradual infertility.
• Typical history for specific causes:
Physical Exam Findings
• General physical examination findings unremarkable unless concurrent systemic disease is present. A complete reproductive examination is necessary and can narrow down the differential list.
• Testicular or epididymal hypoplasia: Young or maiden stallion; small, soft testes on external palpation. May be either unilateral or bilateral cryptorchid.
• Plugged ampullae: Distended or enlarged ampullae on transrectal palpation and ultrasonography. Ampullae may contain hyperechoic areas and a prominent lumen, indicating accumulation of sperm. The tail of the epididymis may be enlarged and turgid.
• Testicular degeneration: Testes may be soft on palpation.
• Ejaculatory failure: Evidence of musculoskeletal or neurologic condition.
Etiology and Pathophysiology
• Testicular hypoplasia: Most often a congenital condition linked to a genetic abnormality or segmental aplasia of the efferent tubules. An intersex condition may be present.
• Plugged ampullae: Physical obstruction in one or both ampullae of unknown cause. This condition may recur after periods of sexual rest in certain stallions.
• Testicular degeneration: Intrinsic factors include defects in the germ cells or supporting cells that may be heritable. Extrinsic factors include temperature changes, endocrine imbalances, vascular insults, toxins, infectious disease, and excessive androgen exposure.
• Ejaculatory failure: Often a result of musculoskeletal pain either before or during ejaculation. Neurologic diseases also cause ejaculatory failure depending on the affected nerve pathway. Behavioral or equipment problems may lead to ejaculatory failure, and these must be evaluated completely in the absence of other clinical signs.
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