Pre-emptive epidural injection of xylazine or amitraz, in horses: clinical and behavioral effects

Xylazine is the alpha(2)-adrenergic agonist more employed by epidural route in horses and it is known that amitraz acts on these receptors. So, clinical and behavioral effects caused by epidural injection of 0.17mg kg(-1) xylazine (GX) or 0.1mg. kg(-1) amitraz diluted in lipidic emulsion (GA) were evaluated in 12 horses. Heart rate and height of the head didn't change; respiratory rate increased from T105 to T360 in GX; rectal temperature increased from T120 to T720 in GA and from T360 to T720 in GX. There is no difference in latency to urine or defecate in both groups. Concerning behavioral changes, amitraz promoted sedation (50%), lip (33.4%) and eye (16.6%) dropping, while xylazine caused ataxia (50%), perineal sweating (33.4%), eye dropping (16.6%) and anal sphincter relaxation (16.6%). So, epidural injection of xylazine or amitraz was considered safe because the clinical and behavioral changes observed are subtle and don't limit its application.