This study was conducted to determine the effects of subanesthetic doses of ketamine given prior to premedication on the quality of anesthesia, recovery, and postoperative pain in horses. Eighteen horses were randomly recruited into three equal groups, S, LK, and HK, wherein saline, ketamine at 0.2 mg/kg body weight (bwt), and ketamine at 0.4 mg/kg bwt were given, respectively, i.v. for 30 min as a continuous rate infusion (CRI). Horses were premedicated with xylazine at 1 mg/kg bwt i.v. and butorphanol at 0.05 mg/kg bwt i.v. after 30 min. Anesthesia was induced using ketamine and midazolam and was maintained with ketamine at 2 mg/kg/h as CRI, and bolus doses of thiopental 5% solution was given i.v. whenever necessary. Preemptive ketamine infusion clinically enhanced the quality of sedation and enabled smooth induction with significantly (P