Background ' Nonsteroidal antiinflammatory drugs (NSAIDs) may contribute to the development of40 gastric ulceration by compromising mucosal protective mechanisms. Newer agents that more selectively41 target the induced isoform of the cyclooxygenase enzyme (COX2) may reduce adverse effects while42 preserving therapeutic benefits of these drugs.4344 Objectives ' Sucrose absorption was used as an objective measure of gastric mucosal permeability to45 compare the effect of oral administration of multiple dose rates of meloxicam and phenylbutazone on46 gastric mucosal integrity in horses.4748 Methods ' Twenty-five lightbreed horses were randomly assigned to five treatment groups, receiving49 placebo, phenylbutazone or three dose rates of meloxicam for 14 days.Sucrose permeability testing was50 performed on Day 0 (prior to treatment) and on Day 13. Horses were monitored by clinical examination,51 clinical pathology, gastroscopy and abdominal ultrasound. All personnel involved with data collection or52 analysis were blinded to treatment.5354 Results ' Phenylbutazone at the manufacturer's recommended dose rate for 14 days was associated55 with a significant increase in gastric permeability to sucrose, suggesting that treatment compromised 56 gastric mucosal permeability. Changes were not observed in other treatment groups.Treatment was not 57 associated with significant differences between groups with respect to ulceration of the squamous or58 glandular mucosa. Peak sucrose concentrations were not correlated with serum total protein or albumin59 concentrations, despite significant decreases in horses receiving phenylbutazone or high doses of60 meloxicam.62 Conclusion and clinical importance ' Phenylbutazone was associated with greater compromise to gastric63 mucosal integrity than meloxicam, suggesting that selective COX2 inhibitors may be safer than no n64 selective agents in horses.