The effects of xylazine, detomidine, acepromazine and butorphanol on equine solid phase gastric emptying rate

Abstract

The aim of this study was to measure the effects of specific commonly used sedative protocols on equine solid phase gastric emptying rate, using the C-13-octanoic acid breath test (C13-OABT). The gastric emptying of a standard C-13-labelled test meal was measured once weekly in 8 mature horses over two 4 week treatment periods. Each horse acted as its own control. In treatment Period 1, saline (2 ml i.v.), xylazine (0.5 mg/kg i.v.), detomidine (0.01 mg/kg i.v.) or detomidine/butorphanol combination (0.01/0.02 mg/kg i.v.) was administered in randomised order after ingestion of the test meal. During treatment Period 2, test meal consumption was followed by saline, xylazine (1.0 mg/kg i.v.), or detomidine (0.03 mg/kg i.v.) administration, or preceded by acepromazine (0.05 mg/kg i.m.) in randomised order. The C-13:C-12 ratio of sequential expiratory breath samples was determined by isotope ratio mass spectrometry, and used to measure the gastric half-emptying time, t(1/2), and duration of the lag phase, t(lag), for each of the 64 tests. In treatment Period 1, detomidine/butorphanol prolonged both t(1/2) and t(lag) with respect to xylazine 0.5 mg/kg and the saline control (P<0.05). In Period 2, detomidine 0.03 mg/kg delayed each parameter with respect to saline, acepromazine and xylazine 1.0 mg/kg (P<0.001). Xylazine 1.0 mg/kg also lengthened t(lag) relative to the saline control (P = 0.0004), but did not cause a significant change in t(1/2). Comparison of treatment periods showed that the inhibitory effect of detomidine on gastric emptying rate was dose related (P<0.05). These findings may have clinical significance for case selection when these agents are used for purposes of sedation and/or analgesia.