Age-related changes in the testes of horses.
Authors: Fukuda T, Kikuchi M, Kurotaki T, Oyamada T, Yoshikawa H, Yoshikawa T
Journal: Equine veterinary journal
Summary
# Age-Related Testicular Changes in Horses: Structural Decline and Fertility Implications Testicular atrophy and fibrosis are common findings in aged stallions, yet the cellular mechanisms underlying these changes remain poorly understood. Fukuda and colleagues examined histological, ultrastructural, and immunohistochemical changes in testicular tissue from eight Thoroughbred stallions ranging from 4 to 24 years of age, comparing younger horses (4–20 years) with two very aged animals (23–24 years). The oldest horses demonstrated significantly elevated collagen deposition in both the seminiferous tubule lamina propria and testicular interstitium (P<0.001), alongside marked thickening of the basal lamina and aberrant changes in myoid cells—the contractile cells supporting sperm production. Rather than simply atrophying passively, myoid cells underwent phenotypic transformation into myofibroblasts, characterised by reduced cytoplasmic actin filaments, altered morphology, and increased secretion of matrix metalloproteinase-2, driving progressive fibrosis. These structural alterations substantially compromise the integrity of the blood-testis barrier and the supportive microenvironment essential for spermatogenesis, providing a biological explanation for the documented decline in fertility and semen quality observed in aged stallions. For practitioners managing breeding stallions or evaluating reproductive function in mature horses, these findings underscore the importance of monitoring testicular ultrasonography and semen parameters from mid-life onwards, as the progressive nature of these changes suggests that early intervention strategies may help preserve reproductive longevity.
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Practical Takeaways
- •Stallions aged 23+ years show progressive testicular fibrosis and structural changes that may compromise fertility and semen quality
- •Age-related testicular degeneration involves transformation of myoid cells into myofibroblasts, which may be a target for future therapeutic interventions
- •Breeding soundness examinations in aged stallions should account for age-related histological changes that may not be apparent on clinical inspection alone
Key Findings
- •Horses aged 23-24 years showed statistically significant increases in collagen fibres in seminiferous tubule lamina propria and testicular interstitium compared to younger horses (P<0.001)
- •Myoid cells in aged horses transformed into myofibroblasts with decreased cytoplasmic actin filaments and secretion of matrix metalloproteinase-2
- •Basal lamina thickening occurred with decreased collagen type IV reactivity in aged horses
- •Myoid cell morphological changes and fibrosis progression suggest functional decline of the blood-testis barrier with advancing age