B. W. Sykes, C. Underwood, R. Greer, C. M. McGowan, P. C. Mills

Conflicting data are presented in the current literature regarding the efficacy of omeprazole for suppressing gastric acidity in the horse. The objective of this study was to investigate the duration of intra-day acid suppression achieved with two doses of omeprazole under two different dietary conditions. A 4-way cross-over design. Six adult, Thoroughbred horses instrumented with percutaneous gastrotomy tubes were used. Intra-gastric pH was measured for continuous 23 hour periods (8.00 am - 7.00 am) for 6 consecutive days (days 0-5). Baseline data was recorded on day 0 and omeprazole was administered on days 1-5. Two doses (1 mg/kg and 4 mg/kg PO once daily) and two diets (a high grain/low fibre (HG/LF) and ad libitum hay (HAY) diet) were studied. Data for the percent time pH was above 4 (%tpH>4) and median intra-day pH was reported for two measurement locations and analysed using generalised estimating equations RESULTS: An effect of both diet and dose was evident with mean %tpH>4 and the mean of the median intra-day pHs typically higher at the higher (4 mg/kg) dose and in HG/LF diet. The overall efficacy of omeprazole in raising intra-gastric pH was good under the HG/LF conditions but relatively poor in the HAY diet. A cumulative effect of dosing, not previously reported in the horse, was observed. The overall efficacy of omeprazole in raising ventral gastric pH was less than previously reported. Both dose and diet may play a role in the efficacy of omeprazole in the horse. Therefore, the use of singular dosing recommendations that encompass all horse types and management conditions may not be appropriate and dosing recommendations that take into account the diet of the horse may be advantageous. This article is protected by copyright. All rights reserved.