Age-Related Changes in the Leydig Cell Population, Seminiferous Tubules, and Sperm Production in Stallions

TLDR: The Leydig cell population increased with age by replacing the noncellular components of the interstitium and did not alter the proportion of the testis occupied by blood vessels, lymph vessels, or seminiferous tubules.

Abstract: Age-related changes in the Leydig cell population of horses between 2 and 20 years old were characterized by a twofold increase in Leydig cell number per gram parenchyma, a threefold increase in Leydig cell number per testis, a threefold increase in Leydig cell volume per gram parenchyma, and a fivefold increase in Leydig cell volume per testis. Due to the increased volume of Leydig cells per gram of testicular parenchyma and the increased size and accumulation of lipofuscin granules in individual cells, the gross appearance of the parenchyma became darker with age. The Leydig cell population increased with age by replacing the noncellular components of the interstitium and did not alter the proportion of the testis occupied by blood vessels, lymph vessels, or seminiferous tubules. Both the diameter and length of seminiferous tubules increased with age. Daily sperm production per testis increased between postpuberty and adulthood yet did not increase significantly beyond adulthood. However, the number of Leydig cells per testis continued to increase in the aging horse. Other significant changes included increases in testicular weight, volume of Leydig cells per testis, seminiferous tubular length per testis, and daily sperm production per testis in April-May compared with February-March.