The prevalence of EGUS in domestic horses is high.1–3 Multiple factors are associated with or have been proposed to contribute to formation of gastric ulcers; these include changes in the production of stomach acid, alterations in the exposure of stomach mucosa to stomach acid, impairment of gastric mucosal blood flow, and bacterial colonization.3,4 The PPI omeprazole is available in a proprietary oral paste formulation, which is the current treatment and preventative of choice owing to its efficacy in reducing acid secretion and ulceration scores, convenient daily dosing, and high margin of safety.5–7 In addition to reducing physical damage to the mucosa, reduction of acidity in the stomach has been proposed to alter gastrointestinal microbiota.8–11 Alterations in gastric microbiota, including decreases in Helicobacter spp, are additional positive effects of PPIs in people and dogs.9,12 However, changes in gastrointestinal microbiota may also contribute to the association between PPI use and increased incidence of gastrointestinal, respiratory, and hematogenous infectious complications in human patients.8,13,14 One study15 of hospitalized foals found an increased incidence of diarrhea and sepsis in association with the use of antiulcer medication, suggesting the potential for infectious complications or dysbiosis as a result of PPI use in horses as well.
The microbiome of the gastrointestinal tract in healthy horses16,17 and microbiota changes associated with management, antimicrobial treatment, and anesthesia of horses18–20 have been previously described. However, to the authors’ knowledge, the potential effects of omeprazole on equine gastrointestinal microbiota have not been investigated. Given the microbiota changes reported following PPI administration in other species and the potential therapeutic and adverse effects associated with these changes, it is important to address this gap in knowledge regarding equine health. The objective of the study reported here was to determine the effects of administration of omeprazole on the fecal and gastric microbiota of healthy adult horses. We hypothesized that oral administration of commercially available omeprazole paste at a dosage of 4 mg/kg, PO, for 28 days would result in a decrease in diversity and shift in composition of the gastric and fecal microbiota of horses during the administration period and that the changes in gastric and fecal microbiota diversity and composition would be reversed 28 days after omeprazole paste administration was discontinued.
Funded by the For the Love of the Horse Research Endowment Fund through University of Georgia Equine Programs. The product used in this study was provided without cost by Merial Ltd. The provider was not involved in study procedures, data analysis, or writing of the manuscript.
The authors thank Londa Berghaus, Lorelai Branch, and Zac Turner for project support.
Analysis of similarity
Equine gastric ulcer syndrome
Operational taxonomic unit
Principle coordinates analysis
Proton pump inhibitor
MedCalc, version 18.5, MedCalc SoftwareBVBA, Ostend, Belgium.
STATA, version 12.1, STATA Corp, College Station, Tex.
GastroGard, Merial Ltd, Duluth, Ga.
QIAmp Fast DNA Stool Mini Kit, Qiagen, Hilden, Germany.
InhibitEX buffer, Qiagen, Hilden, Germany.
Mini-Beadbeater-24, BioSpec Products Inc, Bartlesville, Okla.
MiSeq, Illumina, San Diego, Calif.
QIIME (Quantitative Insights Into Microbial Ecology), version 1.9, version 3.0. Available at: qiime.org. Accessed Jan 7, 2017.
UCHIME, version 4.2, Edgar RC, Haas BJ. Available at: drive5.com/uchime/uchime_download.html. Accessed Jan 7, 2017.
Greengenes database, version gg_13_8, The Greengenes Database Consortium. Available at: greengenes.secondgenome.com. Accessed Jan 7, 2017.
R: A language and environment for statistical computing, version 3.4.0, R Foundation for Statistical Computing, Vienna, Austria. Available at: cran.r-project.org/. Accessed Jan 7, 2017.
nlme, Linear and nonlinear mixed effects models, R package, version 3.1-122, Pinheiro J, Bates D, DebRoy S, et al. Available at: CRAN.R-project.org/package=nlme. Accessed Jan 7, 2017.
Phyloseq, Handling and analysis of high-throughput microbiome census data, R package, version 1.23.1, McMurdie PJ, Holmes S. Available at: bioconductor.org/packages/release/bioc/html/phyloseq.html. Accessed Jan 7, 2017.
edgeR, Empirical analysis of digital gene expression data in R, R package, version 3.18.1, Chen Y, Lun A, McCarthy D, et al. Available at: bioconductor.org/packages/release/bioc/html/edgeR.html. Accessed Jan 7, 2017.
DESeq2, Differential gene expression analysis based on the negative binomial distribution, R package, version 3.6, Love M, Anders S, Huber W. Available at: bioconductor.org/packages/release/bioc/html/DESeq2.html. Accessed Jan 7, 2017.
ggplot2, Create elegant data visualisations using the grammar of graphics, R package, version 2.2.1, Wickham H, Chang W, RStudio. Available at: CRAN.R-project.org/package=ggplot2. Accessed Jan 7, 2017.
ape, Analysis of phylogenetics and evolution, R package, version 5.1, Paradis E, Blomberg S, Bolker B, et al. Available at: CRAN.R-project.org/package=ape. Accessed Jan 7, 2017.
1. Vatistas NJ, Snyder JR, Carlson G, et al. Cross-sectional study of gastric ulcers of the squamous mucosa in Thoroughbred racehorses. Equine Vet J Suppl 1999;29:34–39.
4. Camacho-Luna P, Andrews FM. Equine gastric ulcer syndrome. In: Sprayberry KA, Robinson NE, eds. Robinson's current therapy in equine medicine. 7th ed. St Louis; Saunders-Elsevier, 2015;280–284.
5. Daurio CP, Holste JE, Andrews FM, et al. Effect of omeprazole paste on gastric acid secretion in horses. Equine Vet J Suppl 1999;29:59–62.
6. Andrews FM, Sifferman RL, Bernard W, et al. Efficacy of omeprazole paste in the treatment and prevention of gastric ulcers in horses. Equine Vet J Suppl 1999;29:81–86.
8. Bavishi C, Dupont HL. Systematic review: the use of proton pump inhibitors and increased susceptibility to enteric infection. Aliment Pharmacol Ther 2011;34:1269–1281.
9. Freedberg DE, Lebwohl B, Abrams JA. The impact of proton pump inhibitors on the human gastrointestinal microbiome. Clin Lab Med 2014;34:771–785.
10. Seto CT, Jeraldo P, Orenstein R, et al. Prolonged use of a proton pump inhibitor reduces microbial diversity: implications for Clostridium difficile susceptibility (Erratum published in Microbiome 2016;4:10). Microbiome 2014;2:42.
12. Garcia-Mazcorro JF, Suchodolski JS, Jones KR, et al. Effect of the proton pump inhibitor omeprazole on the gastrointestinal bacterial microbiota of healthy dogs. FEMS Microbiol Ecol 2012;80:624–636.
13. Laheij RJ, Sturkenboom MC, Hassing RJ, et al. Risk of community-acquired pneumonia and use of gastric acid-suppressive drugs. JAMA 2004;292:1955–1960.
14. Graham PL III, Begg MD, Larson E, et al. Risk factors for late onset gram-negative sepsis in low birth weight infants hospitalized in the neonatal intensive care unit. Pediatr Infect Dis J 2006;25:113–117.
15. Furr M, Cohen ND, Axon JE, et al. Treatment with histamine-type 2 receptor antagonists and omeprazole increase the risk of diarrhoea in neonatal foals treated in intensive care units. Equine Vet J Suppl 2012;41:80–86.
16. Proudman CJ, Hunter JO, Darby AC, et al. Characterisation of the faecal metabolome and microbiome of Thoroughbred racehorses. Equine Vet J 2015;47:580–586.
17. Costa MC, Silva G, Ramos RV, et al. Characterization and comparison of the bacterial microbiota in different gastrointestinal tract compartments in horses. Vet J 2015;205:74–80.
18. Schoster A, Mosing M, Jalali M, et al. Effects of transport, fasting and anesthesia on the faecal microbiota of healthy adult horses. Equine Vet J 2016;48:595–602.
19. Daly K, Proudman CJ, Duncan SH, et al. Alterations in microbiota and fermentation products in equine large intestine in response to dietary variation and intestinal disease. Br J Nutr 2012;107:989–995.
20. Harlow BE, Lawrence LM, Flythe MD. Diarrhea-associated pathogens, lactobacilli and cellulolytic bacteria in equine feces: responses to antibiotic challenge. Vet Microbiol 2013;166:225–232.
21. Costa MC, Stampfli HR, Arroyo LG, et al. Changes in the equine fecal microbiota associated with the use of systemic antimicrobial drugs. BMC Vet Res 2015;11:19.
22. Whitfield-Cargile CM, Cohen ND, Suchodolski J, et al. Composition and diversity of the fecal microbiome and inferred fecal metagenome does not predict subsequent pneumonia caused by Rhodococcus equi in foals. PLoS One 2015;10:e0136586.
23. Whitfield-Cargile CM, Cohen ND, Chapkin RS, et al. The microbiota-derived metabolite indole decreases mucosal inflammation and injury in a murine model of NSAID enteropathy. Gut Microbes 2016;7:246–261.
24. Caporaso JG, Kuczynski J, Stombaugh J, et al. QIIME allows analysis of high-throughput community sequencing data. Nat Methods 2010;7:335–336.
26. Edgar RC, Haas BJ, Clemente JC, et al. UCHIME improves sensitivity and speed of chimera detection. Bioinformatics 2011;27:2194–2200.
27. DeSantis TZ, Hugenholtz P, Larsen N, et al. Greengenes, a chimera-checked 16S rRNA gene database and workbench compatible with ARB. Appl Environ Microbiol 2006;72:5069–5072.
29. McMurdie PJ, Holmes S. phyloseq: an R package for reproducible interactive analysis and graphics of microbiome census data. PLoS One 2013;8:e61217.
30. Robinson MD, McCarthy DJ, Smyth GK. edgeR: a bioconductor package for differential expression analysis of digital gene expression data. Bioinformatics 2010;26:139–140.
32. Perkins GA, den Bakker HC, Burton AJ, et al. Equine stomachs harbor an abundant and diverse mucosal microbiota. Appl Environ Microbiol 2012;78:2522–2532.
33. Sung J, Kim N, Kim J, et al. Comparison of gastric microbiota between gastric juice and mucosa by next generation sequencing method. J Cancer Prev 2016;21:60–65.
35. Schoster A, Staempfli HR, Guardabassi LG, et al. Comparison of the fecal bacterial microbiota of healthy and diarrheic foals at two and four weeks of life. BMC Vet Res 2017;13:144.
36. Weese JS, Holcombe SJ, Embertson RM, et al. Changes in the faecal microbiota of mares precede the development of post partum colic. Equine Vet J 2015;47:641–649.
38. Kuhl J, Winterhoff N, Wulf M, et al. Changes in faecal bacteria and metabolic parameters in foals during the first six weeks of life. Vet Microbiol 2011;151:321–328.
39. Harlow BE, Lawrence LM, Hayes SH, et al. Effect of dietary starch source and concentration on equine fecal microbiota. PLoS One 2016;11:e0154037.
40. Bordin AI, Suchodolski JS, Market ME, et al. Effects of administration of live or inactivated virulent Rhodococccus equi and age on the fecal microbiome of neonatal foals. PLoS One 2013;8:e66640.
41. Bond SL, Timsit E, Workentine M, et al. Upper and lower respiratory tract microbiota in horses: bacterial communities associated with health and mild asthma (inflammatory airway disease) and effects of dexamethasone. BMC Microbiol 2017;17:184.