A quantitative histological study of changes in the bovine testis and epididymis associated with age.

Quantitative histological studies were performed on the testis and epididymis of 80 normal bulls from beef herds in tropical Australia. Four age groups, ranging from nine months to over 10 years were established. Volumetric proportions of parenchymal and collagenous tissues, and tubular or duct surface to tissue volume ratios were determined at the dorsal, middle and ventral testicular regions and at the head, body and tail of the epididymis for each group. Detailed volumetric analyses of the relative volumes of particular parenchymal and stromal elements were made a the middle testicular region. Lymphoid and plasma cell populations were compared in all regions, including the efferent ducts. Differences in the distribution of testicular parenchyma and collagen were found; the dorsal region had more parenchyma and less collagen than the middle and ventral areas. Progressive intertubular fibrosis attributed to age was quantified; it was most marked ventrally. Reductions in the relative volumes of germinal cells, Sertoli cells, tubular cytoplasm and parenchyma, and in tubular surface to testis volume ratios with advancing age, indicated a decrease in the capacity per unit volume of testis to produce sperm. Increased immunocyte populations in the efferent duct region in young bulls were attributed to initial antigenic exposure. Increased antigenic exposure, in association with senile degenerative changes of the genitalia, might have caused the increased immunocyte populations seen in very old bulls.