The objective of this study was to evaluate the analgesic, sedative and muscle relaxation effects, as well as other side effects of medetomidine when used as caudal epidural agent in the horse. Ten healthy adult mixed breed horses (8 mare, 2 stallion) weighing 310±28 kg (mean ±SD) and 6-13 years of age were selected for this experiment. Medetomidine l5pg/kg diluted with normal saline and adjusted to 8 ml was injected in the first intercoccygeal epidural space. The onset and duration of sedation and analgesia recorded after injection. HR, RR, rectal temperature and an ECG were also recorded before and 10, 20, 30, and 60 minutes after injection. Assessment of analgesia was performed by pin pricking in the tail and perineal region. Data were analyzed using paired student t test and P<0.05 was considered significant. Medetomidine did not show good caudal or perineal analgesia in this study and although no surgery performed but it seemed the analgesia was not quite sufficient for surgery. Systemic sedative effects of medetomidine occurred after 7 to 10 minutes by drooping of the lower lip and decreasing head height. Mild ataxia was also observed in some animals by leaning hind limbs to the stock. Urination and relaxation of the penis was occurred in 2 horses. HR decreased significantly (P<0.05) from 42±10.1 bpm (base value) to 36±9, 25± 1.91, 25.5±0.45 and 24.75±0.37 at 10, 20, 30 and 60 minutes respectively. A second degree AV block was observed in one horse. No significant changes were observed in RR and rectal temperature. The results of this study showed that the cardio respiratory effects of caudal epidurally injected medetomidine (l5pg/kg) in the horse are minimal and in safe margins, but this injection alone could not provide surgical analgesia in perineal region.
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