Alpha2 Agonist Sedation and Yohimbine Reversal in Stallions: Effects on Seminal Parameters in a Controlled Crossover Study.

BACKGROUND: Transrectal ultrasonography during stallion andrological examinations often requires sedation, yet the effects of alpha2-agonist protocols and their pharmacological reversal on ejaculate characteristics remain unknown. OBJECTIVES: This study aimed to evaluate whether sedation with xylazine and detomidine followed by yohimbine reversal alters macroscopic, kinetic, or flow-cytometric seminal parameters in stallions. It was hypothesized that the sedation-reversal protocol would not impair seminal quality. METHODS: Five healthy stallions were assessed in a three-period crossover design, totaling 15 ejaculates per treatment. Subjects received three treatments: CONTROL (saline/saline), GROUP 1 (xylazine + detomidine/yohimbine), and GROUP 2 (saline/yohimbine). Yohimbine alone increased gel-inclusive and gel-free ejaculate volumes (P < 0.05) and reduced sperm concentration per milliliter (P < 0.05), while total sperm count remained unchanged. Sperm kinetics did not differ among treatments. RESULTS: Flow cytometric analyses revealed reductions in plasma membrane stability and mitochondrial membrane potential in GROUP 2 (P < 0.05), whereas mitochondrial superoxide anion generation was unaffected. Post-hoc power analysis indicated power ≥ 80% for flow cytometric variables, but limited power for sperm concentration parameters. Sedation with xylazine and detomidine followed by yohimbine reversal did not alter seminal quality under these conditions. CONCLUSION: These findings support that sedation with xylazine and detomidine followed by yohimbine reversal did not alter seminal quality under the conditions of this exploratory study, although larger trials are required to evaluate fertility outcomes.