Low Daily Sperm Output Per Ml of Testis as a Diagnostic Criteria for Testicular Degeneration in Stallions

Abstract

SUMMARY Testicular degeneration is a major cause of poor fertility in stallions. Palpation and measurement of the testes are common methods used to diagnose testicular degeneration. When small testes of abnormal consistency (usually soft) are detected, a diagnosis of testicular degeneration can be confirmed. However, since testicular degeneration varies greatly in severity, many stallions with testicular degeneration will not have small, soft testes. In fact, less severe cases of testicular degeneration cannot be detected by palpation and measurement of testes, and require histologic confirmation (e.g., testicular biopsy) of the diagnosis. Since testicular degeneration results in fewer sperm being produced during spermatogenesis, non-invasive procedures for estimating spermatogenic efficiency (i.e., number of sperm produced per unit of testis) can be used to diagnose testicular degeneration. Specifically, we propose that once extragonadal sperm reserves are stabilized, the number of sperm in ejaculates per ml of testis is a useful non-invasive method for the practitioner to determine whether testicular degeneration is present. To support our contention that a non-invasive method of estimating spermatogenic efficiency (i.e., calculation of daily sperm output per ml of testis) is a useful criteria for diagnosing testicular degeneration, we used data from 3 trials to characterize the relationship between degeneration of germ cells, spermatogenic efficiency and output of normal sperm in ejaculates. In the first trial, the relationship between testicular germ cell degeneration rates and efficiency of sperm production was investigated by performing histomorphometric analyses on testes obtained from 88 mature stallions during the breeding and nonbreeding seasons. A negative correlation existed between germ cell degeneration rate and spermatogenic efficiency at the level of the testes (expressed as daily sperm production per ml of testis; DSP/ml) (r = - 0.87; P