How to Investigate Azoospermia in Stallions

1. Introduction
In a review of ejaculatory dysfunction, McDonnell1 reported that ~25% of stallions referred to a fertility clinic had evidence of ejaculatory problems. The vast majority of cases were anejaculatory (failure to ejaculate). Less than 1% of horses in that survey were truly azoospermic (i.e., ejaculated seminal fluids devoid of sperm). Failure to ejaculate sperm can be a troublesome problem that requires accurate diagnosis, determination of prognosis for correction (sometimes necessitating retirement as a breeding stallion), and arduous treatment and/or breeding management to correct.^2,3  Figure 1 represents an attempt at a schematic overview of an approach to diagnosis of lack of sperm in ejaculates.

2. Confirming Ejaculation
Clinical evaluation of stallions failing to produce sperm in ejaculates should begin with determining whether or not ejaculation is occurring. Lack of secondary signs of ejaculation (i.e., flagging of the tail, treading on hindlimbs, and presence of strong urethral pulsations) followed by dismount with the glans penis still partially engorged and an absence of sperm in seminal fluids suggest that the stallion did not ejaculate.³ A number of reports describe therapy indicated for ejaculation failure, but they are not the subject of this report. Briefly, they include breeding and/or pharmacological management to increase sexual stimulation before and during the breeding process, treatment and/or breeding management to minimize potential musculoskeletal pain that could interrupt the emission and ejaculatory process, and pharmacologic manipulation to lower the threshold to emission and ejaculation.^1–3 Techniques used to manage repeated ejaculatory failure can be arduous and time consuming, and they are reviewed by Varner et al.³ [...]