Ejaculatory failure in a halter stallion due to dorsal displacement of soft palate

Exercise-induced dorsal displacement of soft palate (DDSP) commonly occurs in racehorses, characterized by decreased performance; 1 however, it has not been identified as a cause for failure of ejaculation. In May 2019, a 5 year old maiden American Quarter Horse halter stallion was presented for failure of ejaculation. During breeding soundness examination, stallion demonstrated normal libido and mounting behavior during repeated mounts on phantom, but never ejaculated. While mounted, stallion expressed labored breathing that owner had noticed during previous breeding attempts. Manual palpation of scrotum, accessory sex glands, and penis were normal. An echocardiogram and chemistry analysis for lactic acid, alkaline phosphatase, and creatine kinase were normal. Static endoscopy of larynx was normal, but dynamic endoscopy during stallion’s mount on phantom revealed 50 - 70% of airway became blocked by DDSP. To correct this condition, a laryngeal tie-forward procedure was performed. Following 2-week postoperative recovery under owner’s supervision, stallion was able to ejaculate normally and repeatedly. Ejaculation disorders in stallions were attributed to physical, musculoskeletal, psychogenic, or neurologic causes; 2 apparently, DDSP has not been reported before as a cause. Halter-type stallions with ejaculatory dysfunction have been observed to exhibit labored breathing during and following breeding and was assumed to be a “common” breed characteristic. Occurrence of DDSP is associated with exercise intolerance; however, exact etiology is unknown. 1 In this stallion, increased activity was associated with breeding-induced displacement of soft palate above epiglottis. As a result, stallion was unable to complete ejaculation, due to blockage of airway. Following surgical correction, stallion was able to ejaculate. Ejaculatory dysfunction in stallions can be difficult to assess; therefore, DDSP should be considered as an underlying cause, especially when abnormal respiratory sounds are heard during breeding.

Keywords: Halter stallion, ejaculatory failure, DDSP

References

1. Cercone M, Olsen E, Perkins JD, et al: Investigation into pathophysiology of naturally occurring palatal instability and intermittent dorsal displacement of the soft palate (DDSP) in racehorses: Thyro-hyoid muscles fatigue during exercise. PLoS ONE 2019;14(10): e0224524.
2. McDonnel SM: Ejaculation. Physiology and dysfunction. Vet Clin N Am-Equine 1992;8:57-70.

This manuscript was originally published in the journal Clinical Theriogenology Vol 12(3) Sept 2020.  Clinical Theriogenology is the official journal of the Society for Theriogenology (SFT) and the American College of Theriogenologists (ACT).  This content has been reproduced on the IVIS website with the explicit permission of the SFT/ACT.