BACKGROUND: Flunixin meglumine (FM) is commonly used in painful conditions in horses
however, it may contribute to equine gastric ulcer syndrome (EGUS). Some veterinarians combine omeprazole (OME) and FM to reduce EGUS risk. However, the efficacy and safety of this combination in Mongolian horses with chronic lameness remain unknown. OBJECTIVES: To investigate the changes in lameness and EGUS scores in Mongolian horses through the comparison of three treatment strategies: FM, FM + OME and placebo treated control (CON) and to assess the effects of these treatments on gastric fluid pH, serum total protein, albumin and oxidative stress markers (MPO, SOD, CAT). STUDY DESIGN: In vivo experiments. METHODS: Eighteen Mongolian horses with initial American Association of Equine Practitioners lameness scores ≥3 of 5 were selected and equally divided into the placebo (CON), FM (1.1 mg/kg IV q. 24 h) and FM + OME (4 mg/kg PO q. 24 h) treatment groups in a randomised block design. During 15 days of treatment, weekly gastroscopy and physiological and biochemical tests were performed. Stomach tissues were harvested from two horses from each group for histopathological examination with haematoxylin and eosin, Masson's trichrome and periodic acid-Schiff (PAS) staining. RESULTS: FM (median 1.0, interquartile range 0.0-1.0
p <
0.001) and FM + OME (1.0, 1.0-1.0
p <
0.001) significantly decreased lameness scores compared with CON (3.0, 3.0-4.0). Compared with CON (EGGD: 0.0, 0.0-1.0, p <
0.001
PG1: mean 231.9 ± standard deviation 25.2 ng/mL, p <
0.001) or FM + OME (EGGD: 0.8, 1.0-1.3, p = 0.003
PG1: 207.08 ± 34.85 ng/mL, p <
0.001), FM significantly increased equine gastric glandular disease (EGGD) grade (3.0, 2.0-3.3) and pepsinogen 1 (PG1) content (372.2 ± 33.2 ng/mL, p <
0.001). Compared with CON (total protein: 70.1 ± 2.9 g/L
albumin: 37.0 ± 3.0 g/L
Gastrin-17: 482.5 ± 48.1 pg/mL), FM significantly reduced total protein (62.8 ± 2.9 g/L, p = 0.003), albumin (31.5 ± 2.3 g/L, p = 0.01) and Gastrin-17 (GT-17) content (284.6 ± 57.2 pg/mL, p <
0.001). Compared with FM (EGGD: 3.0, 2.0-3.3
pH: 2.4 ± 0.3), FM + OME significantly decreased the EGGD grade (0.8, 1.0-1.3
p = 0.003) and significantly increased gastric fluid pH (7.4 ± 0.2
p <
0.001). FM + OME (207.1 ± 34.9 ng/mL) significantly decreased PG1 content compared with FM (372.24 ± 33.25 ng/mL
p <
0.001). Histopathology revealed that 15 days of FM treatment led to gastric lesions in horses, which were mitigated by combining with OME. MAIN LIMITATIONS: Individual differences among horses were large, but the sample size was small and sampling was infrequent. CONCLUSIONS: Compared with FM alone, use of FM + OME did not impact the reduction in lameness scores with therapy, but reduced the occurrence of EGGD in Mongolian horses. When used to manage chronic lameness, FM + OME might protect against FM-induced EGGD by increasing the gastric pH and decreasing serum PG1 content.