Sperm Accumulation in a Stallion

             A 4yo Standardbred stallion was examined for breeding soundness.  The stallion was classified as an Unsatisfactory Prospective Breeder based on <5% total motile, 0% progressively motile, and <30% morphologically normal sperm that persisted over several days of intermittent semen collections.^1,2  Additionally, 92% of the sperm were nonviable.  Palpation and ultrasonography of the genital tract revealed no abnormalities. Specifically, the testicles and ampullae were normal.

             Sperm accumulation was suspected.  Frequent semen collections, ampullary massage, and intravenous oxytocin were initiated to clear accumulated sperm.³  Following five days of 3-4 x daily semen collections, progressive motility improved to over 50%.  The percentage of normal sperm remained low due predominately to midpiece abnormalities.  The improvement in sperm motility resulted in each ejaculate containing at least one minimum insemination dose. 

             Occasional episodes of flank-biting, bucking, and kicking, previously attributed to stallion-like behavior, were mentioned upon admission.  Behavioral analysis of continuous video surveillance samples suggested acute caudal abdominal pain.  Transabdominal ultrasonography revealed a 5cm nephrolith in the left kidney.  The nephrolith was removed laparoscopically, allowing the stallion to rapidly return to acceptable fertility.

             Although this stallion did not possess the classically cited signs of sperm accumulation (e.g., high percentage of detached heads, distended ampullae),^4,5 the poor sperm motility, variable sperm numbers, and high percentage of nonviable sperm in the face of apparently normal testicles suggested the problem.^6,7  Accurate diagnosis is critical since this condition is typically reversible and affected stallions may return to acceptable fertility.

             Additionally, this case demonstrates the importance of careful evaluation of behavior.  This behavior had historically been incorrectly interpreted as normal stallion-like aggression.  Objective evaluation identified a significant physical abnormality.  Because nephroliths can cause intermittent fevers, removal may result in improvements to sperm morphology and so may further improve fertility.

1.         Kenney RM, Hurtgen JP, Pierson RH, et al.  Clinical fertility evaluation of the stallion.  J Soc Therio 1983;9:7-62.

2.         Little, TV, Woods GL.  Ultrasonography of accessory sex glands in the stallion.  J Reprod Fertil, Suppl 1987;35:87-94.

3.         Love CC, Riera FL, Turner RMO.  Sperm occluded (plugged) ampullae in the stallion.  In: Proceedings of the Annual Meeting of the Society for Theriogenology 1992;117-127.

4.         Sullivan JJ, Pickett BW.  Influence of ejaculation frequency of stallions on characteristics of semen and output of spermatozoa.  J Reprod Fertil, Suppl 1975;23:29-34.

5.         Weber JA, et al. Changes in accessory sex glands of stallions after sexual preparation and ejaculation.  JAVMA 1990;196:1084-1089.

6.         Youngquist RS.  Examination of the male reproductive tract:  Evaluation of potential breeding soundness.  In:  Current Therapy in Large Animal Theriogenology
            1997;12-15.