equis - Articles
Testis: hypoplasia
Introduction
- Failure of the testis to develop to normal size, accompanied by failure of the epididymis to reach normal size.
- Normally evidenced by failure of pre-pubertal testes to develop at puberty. Sometimes even pre-pubertal testes may be noticeably underdeveloped.
- Can be unilateral or bilateral.
- Relatively common pathologic entity in stallions. A number of authors state that hypoplastic testes are predisposed to testicular degeneration.
- Specific breed predilections have not been studied critically.
- Causes: suspected causes include abnormal karyotype; in-utero infection or toxins; zinc deficiency; hormonal insufficiency; disrupted testicular descent; vascular disturbances.
- Signs: one or both testes can be involved with varying degrees of hypoplasia due to reduction in the quantity of seminiferous epithelium. Changes evident on semen evaluation.
- Diagnosis: full clinical examination; ultrasonography; +/- testicular biopsy; cytogenetic studies may be indicated if chromosomal abnormality suspected.
- Treatment: none.
Presenting signs
Either In association with cryptorchidism Testis: cryptorchidism (both intersex and idiopathic forms). Or As an unexplainable phenomenon of intrascrotal testes, 3% of 1,000 stallions in one report.- Can be mild to severe.
- Can involve one or both testes. If both testes involved, fertility impaired / infertile.
Age predisposition
- Diagnosis cannot be made until after puberty (3 years+).
Breed/Species predisposition
- Testes of male equine hybrids (mules Mule or hinnies) are typically hypoplastic.
Cost considerations
- Loss of potential stallion (infertile) or decreased fertility.
- Investigation costs.
Pathogenesis
Etiology
- Probably a multifactorial disease.
- Can result from primarily congenital aberrations Reproduction: gonadal dysgenesis.
- Suspected causes include abnormal karyotype; in-utero infection or toxins; zinc deficiency; hormonal insufficiency; disrupted testicular descent; vascular disturbances.
External influences
- Infections.
- Intoxications.
- Malnutrition.
- Endocrinologic disturbances.
- Irradiation.
- Impaired thermoregulation.
- Male equine hybrids (mules or hinnies).
- Abdominal or inguinal cryptorchidism Testis: cryptorchidism.
- Congenitally short cremaster muscles or excessive intrascrotal fat.
Pathophysiology
- Characterized by incomplete gonadal development.
- Accelerated development of testis into a sexually functional organ does not normally begin until puberty → derangement of numerous prepubertal events can result in testicular hypoplasia.
Abnormal primordial germ cell activity during fetal life
- May be caused by:
- Inadequate proliferation in the yolk sac.
- Improper migration en route to the fetal gonad.
- Insufficient multiplication/inordinate degeneration after arrival at the gonad.
Post-natal disruption of the germinal epithelium
- Mild forms of testicular hypoplasia, most affected seminiferous tubules exhibit active spermatogenesis that progresses to the primary spermatocyte stage or beyond.
- Isolated tubules remain completely hypoplastic.
- Resulting fertility is determined by the degree of hypoplasia.
- Severe hypoplasia is characterized by a pre-ponderance of completely hypoplastic seminiferous tubules.
Diagnosis
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Treatment
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Prevention
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Outcomes
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Further Reading
Publications
Refereed papers
- Recent references from PubMed and VetMedResource.
- Pozor M et al (2017) Relationship between echotextural and histomorphometric characteristics of stallion testes. Theriogenology 99, 134-145 PubMed.
- Pozor M (2005) Diagnostic applications of ultrasonography to stallion's reproductive tract. Theriogenology 64 (3), 505-9 PubMed.
- Faber N F & Roser J F (2000) Testicular biopsy in stallions: diagnostic potential and effects on prospective fertility. J Reprod Fertil Suppl (56), 31-42 PubMed.
- Strong M et al (1997) Monorchidism in two horses. Aust Vet J 75 (5), 333-335 PubMed.
- Parks A H et al (1989) Monorchidism in the horse. Equine Vet J 21 (3), 215-217 PubMed.
- Santchi E M et al (1989) Monorchidism in three colts. JAVMA 194 (2), 265-266 PubMed.
Other sources of information
- Arighi M (2011) Developmental abnormalities of the male reproductive tract. In: Equine Reproduction. 2nd edn. Eds: McKinnon A O, Squires E L, Vaala W E & Varner D D. Wiley Blackwell. pp 1109-1111.
- Johnson L, Griffin C E & Martin M T (2011) Spermatogenesis. In: Equine Reproduction. 2nd edn. Eds: McKinnon A O, Squires E L, Vaala W E & Varner D D. Wiley Blackwell. pp 1026-1052.