Pharmacologically Induced Ejaculation in Stallions

Since Drs. McDonnell and Love pioneered research into Pharmacologically Induced Ejaculation in Stallions in the 1990s1, “chemical collection” has been a tool in many advanced stallion manager’s and veterinarian’s collection tool box. The original research produced a tried-and-tested protocol involving Imipramine and Xylazine, and ultimately was considered successful in about 70% of stallions, 70% of the time, so around half the time when the two statistics were combined. Newer combinations have been tried since then, and this research looks at the results seen with some of those protocols.

Pharmacologically Induced Ejaculation in Stallions - chemical collection - drug bottles on counterBackground:

  • Pharmacologically induced ejaculation provides an alternative semen collection method for stallions with physical or behavioral conditions preventing normal mounting or copulation
  • Multiple protocols exist with variable outcomes; active area of research

Study Design:

  • 8 healthy stallions, mean age 8.7 years (range 5–22); 2-day intervals between treatments
  • Eight protocols tested, with and without 10-minute sexual pre-stimulation via estrous mare teasing:
    • Xylazine + Butorphanol — without pre-stimulation
    • Detomidine + Butorphanol — without pre-stimulation
    • Detomidine + Butorphanol + Oxytocin — without pre-stimulation
    • Xylazine + Detomidine + Butorphanol + Oxytocin — without pre-stimulation
    • Imipramine (oral) → Xylazine + Butorphanol — sequential administration
    • Imipramine (oral) → Detomidine + Butorphanol + Oxytocin — sequential administration
    • Xylazine + Butorphanol — with pre-stimulation
    • Detomidine + Butorphanol + Oxytocin — with pre-stimulation

Key Results:

  • Highest ejaculation rates: Imipramine + Xylazine + Butorphanol (62.5%) and Imipramine + Detomidine + Butorphanol + Oxytocin (50%)
  • No ejaculations in Detomidine + Butorphanol alone or Xylazine + Detomidine + Butorphanol + Oxytocin groups
  • No significant difference in time to ejaculation across protocols
  • Sexual pre-stimulation only increased ejaculate volume in the Xylazine + Butorphanol group
  • Highest sperm concentrations achieved with Detomidine- and Imipramine-containing protocols

Conclusions:

  • No single protocol for pharmacologically induced ejaculation (“chemical collection”) in stallions is universally effective; multiple sequential trials are recommended upon initial failure
  • Imipramine-based combinations show most promise for ejaculation induction

(Garza J, Del Angel S, Gallelli MF, Miragaya M. 2025. Pharmacologically induced ex copula ejaculation in stallions: assessment of new combined protocols. JEVS 145:105288 – Presented in Association with and by Permission of the International Society for Equine Reproduction)

References:

1: McDonnell SM, Love CC. 1991. Xylazine-induced ex copula ejaculation in stallions. Theriogenology. 36:73–6