Effect of xylazine, detomidine, and a combination of xylazine and butorphanol on equine duodenal motility

Abstract

Objective - To evaluate the effect on equine duodenal motility of some analgesic agents commonly used to treat colic. Animals - 4 healthy adult healthy horses - 2 mares and 2 geldings - which were carrying an indwelling gastric cannula made of silastic rubber. One horse also carried 2 long-term indwelling bipolar electrodes that had been sutured onto the doudenum and jejunum. Procedure - To ensure an empty stomach, solid food was withheld from horses for around 20 hours prior to an experiment. Using videoendoscopic guidance, an 8-F catheter with 3 small, discrete pressure sensors was passed through the gastric cannula and directed into the proximal portion of the duodenum. Deflection of the recording pen, to which the catheter was attached, indicated a motile event in that section. Drugs (treatment) were given into the jugular vein in a randomized block design, 1 treatment/experiment, after a 1-hour baseline recording. Treatments were: 2 ml of 0.9% NaCl, xylazine (XYL, 0.5 mg/kg of body weight), detomidine (DET, 0.0125 mg/kg), or a xylazine/butorphanol combination (XYB, 0.5/0.5 mg/kg). Each horse received each treatment twice. All positive pressure peaks > 5 mm of Hg recorded from the most proximal sensor on the catheter were counted in 15-minute blocks. Each mean 15-minute posttreatment value was compared with the baseline value for that specific treatment. Results - There was no significant difference between baseline values. All treatments significantly (P < 0.05) reduced frequency of pressure peaks below their respective pretreatment values, but to variable degrees and durations. Comparatively, XYL had the least effect, with mild, though significant, reduction for only the first 30 posttreatment minutes; DET and XYB caused a significant marked reduction for 1 hour after treatment. Conclusions - The profound suppressive effect of a routine dose of detomidine or xylazine/butorphanol combination on equine duodenal motility must be considered when using these agents for management of colic, especially when encouragement of intestinal motility is desirable.