Understanding the role of diet and enteric bacteria in the development of feline diarrhea (Sponsored by Nestle Purina)


This paper reviews what is known about feline inflammatory bowel disease, with particular focus on the role of commensal and pathogenic intestinal bacteria as well as diet in the management of the disease.

Feline inflammatory bowel disease (IBD) applies to a number of poorly understood enteropathies characterized by the infiltration of inflammatory cells into the gastrointestinal (GI) mucosa. The cellular infiltrate is composed of variable populations of lymphocytes, plasma cells, eosinophils, and neutrophils that can be distributed throughout the GI tract.1-3 In severely affected cats, this infiltrate may be accompanied by changes in the mucosal architecture, including villus atrophy, fusion, fibrosis, and lymphangiectasia.

Although IBD appears to be a common clinical problem in cats, little is known about the etiopathogenesis or the local and systemic consequences of the disease, including the development of lymphoma and nutritional deficiencies.4 In addition, the nature of inflammation associated with IBD is just beginning to be characterized beyond the visible changes in gross histopathology that have been described.5-11

Feline IBD is characterized by persistent clinical signs consistent with GI disease (e.g. vomiting, anorexia, weight loss, diarrhea) that occur concurrently with histologic evidence of mucosal inflammation.12 Many cats with IBD have concurrent inflammation of the liver and pancreas—a phenomenon called triaditis.13 The median age of cats presenting with IBD is around 7 years, and most cats present with a history of these signs occurring intermittently for weeks to years. Purebred cats, such as the Siamese and Abyssinian, may be overrepresented, but definitive breed predilections have not been reported. There is no reported predilection based on sex.

This paper reviews what is known about feline IBD, with particular focus on the role of commensal and pathogenic intestinal bacteria as well as diet in the management of the disease.

The role of bacteria

In humans and experimental animals, recent studies indicate a strong association between the development of IBD and a breakdown of normal tolerance mechanisms, host susceptibility, and enteric microflora.14-17 It is likely that these same factors are important in feline IBD. (See "Are Bacteria a Key Component?" on page 4) It is clear that modulation of the enteric microenvironment in humans with IBD has been shown to reduce proinflammatory cytokines in the mucosa and, therefore, decrease the inflammatory response.18 In humans, IBD therapy has included antibiotics with immune-modulating capacity, prebiotics, probiotics, and immunosuppressants as well as other drugs that modify cytokine release.17,19

Unfortunately, studies assessing modulation of enteric flora (using probiotics, prebiotics, or other specific therapy for cytokines) in cats with IBD are only in the early stages. Nevertheless, few studies have shown that intestinal microbiota in cats with IBD are clearly different from those in normal cats and often the difference is a decrease in normal commensals (e.g. bifidobacteria, lactobacilli) and an increase in pathogenic species.6,9 At this time, therapy for IBD in cats continues to include inflammatory suppression and antibiotic therapy. The most effective IBD therapies include corticosteroids (i.e. prednisolone or methylprednisolone, 1 to 2 mg/kg PO Q 12 H) or other drugs that interrupt the proinflammatory pathways active in the gut. In cats that are intolerant of corticosteroids, budesonide therapy may be a reasonable choice.

Alternatively, in cats in which corticosteroids are no longer effective or are causing morbidity (e.g. diabetes), immunosuppressive therapy may be necessary and is often effective. The two drugs most commonly recommended and effective for cats in this setting are cyclosporine and chlorambucil.

Antibiotic therapy with 5 to 10 mg/kg PO Q 12 H of metronidazole has been effective for a number of years and continues to be recommended as initial therapy for IBD.12,20 There is also a widely held belief that metronidazole is effective not only because of its antibacterial properties but because of concurrent immune-modulating properties. Some data support these ideas, but the specific role of metronidazole as treatment for IBD is still not completely known. Because metronidazole may be poorly tolerated and has potential for serious adverse effects, it should not be given indefinitely. Another antibiotic that may be useful in cats with presumed IBD is tylosin at a dose of 10 to 20 mg/kg PO Q 12 H; however, less is known about the effects of tylosin in cats when used long-term.21,22

Finally, data in humans with IBD are increasingly showing that probiotics and antioxidant prebiotic nutraceuticals may be important components of therapy.19 At this time, it is difficult to make specific recommendations concerning the probiotic or nutraceutical therapy with the greatest benefit because of the paucity of studies in cats with IBD and the species-specific nature of probiotics and their effects. However, probiotics that provide an immune-modulating effect or that increase the number of beneficial species while competing against pathogens might be expected to be helpful. In several studies in kittens, probiotics containing Enterococcus faecium (SF68) appeared to improve immune function and had better responses to therapy when exposed to enteric protozoa.23 Furthermore, whereas probiotic therapy alone would not be expected to produce clinical remission, cats undergoing long-term therapy for IBD may benefit from the addition of probiotics to their treatment regimen.

The role of dietary management

The use of diet to help manage GI disease is not a new concept, but the type of diet to use has become an increasingly complex issue. In many, if not most, cats with mild IBD, especially those without significant infiltrate of inflammatory cells (mild to moderate infiltrate) or without significant weight loss or other morbidity, the best approach is to feed a highly digestible diet or to change the diet to one with fewer additives, flavorings, or other substances that may be associated with food intolerance. Many cats (nearly two-thirds in one study) with chronic diarrhea have complete resolution of clinical signs when fed a highly digestible diet.24,25

Highly digestible diets are not defined in a regulatory sense but generally indicate a product with protein digestibility of greater than 85% (typical diets are 78% to 81%) and fat digestibility of greater than 90% (typical diets are 77% to 85%). These diets are designed to provide food that is easy to digest because it has moderate to low fat, moderate to increased protein, and moderate to decreased carbohydrates; may have additives to improve intestinal health, such as soluble fibers, omega-3 fatty acids, and increased antioxidant vitamins; and contain no gluten, lactose, food coloring, preservatives, and similar additives. Many different brands fall under the category of "highly digestible," but they are not all alike.

The protein digestibility of a diet is one of the key factors that can determine its success in cats with IBD. In general, meat-source proteins and diets containing meat meals are more digestible than plant-source proteins, and animal proteins are more digestible than meat by-products. In addition, to increase digestibility of foods in cats, the number and amount of carbohydrates in the food are decreased—a single-source carbohydrate food is better than foods with many different sources, and highly digestible carbohydrate sources are better than complex plant source carbohydrates. Therefore, when one diet from this category is not accepted or seems to make the diarrhea worse, it cannot be assumed that all diets in this category will be ineffective and unaccepted. Diets from different manufacturers have various formulations. (See "Diets Designed to Promote GI Health" on page 5)

Novel antigen or elimination diets

Allergens and intolerance are the most common adverse reactions cats have to food. Food allergy or hypersensitivity is an adverse reaction to a food or food additive with a proven immunologic basis. In contrast, food intolerance is a nonimmunologic abnormal physiologic response to a food or food additive. Food poisoning, food idiosyncrasy, and pharmacologic reactions to foods also fall under the category of food intolerance.

The specific food allergens that cause problems in cats have been poorly documented, with only 10 studies describing the clinical lesions associated with adverse reactions.24,26,27 In these reports, more than 80% of cases were attributed to beef, dairy products, or fish.

The incidence of food allergy in cats remains unknown but is estimated to be only 15% to 20% of all food-related causes of diarrhea.27 However, food intolerance is believed to contribute to 60% to 65% of feline diarrhea cases. In two separate studies, a majority of cats responded to dietary therapy with a highly digestible diet.25,28

The causes of dietary intolerance that need to be carefully considered in feline diets are primarily protein and carbohydrates—both sources and amounts. The diagnosis of both food allergy and intolerance is based on a dietary elimination trial. The major difference between these two types of adverse food reactions is the length of time on the diet required to achieve a response. Cats with food allergy may require six to 12 weeks on the elimination diet before an improvement will be seen. Most authors report that one to two weeks are required to rule out intolerance.

Various commercial and homemade elimination diets, as well as diets formulated with hydrolyzed proteins, may be used in cats with suspected food allergy or intolerance. The key is to select a diet that has a novel protein source based on a careful dietary history and is balanced and nutritionally adequate (commercial diets are best for this); however, a homemade elimination diet may be necessary to find an appropriate test diet. If a homemade diet must be used for long-term therapy, a complete and balanced diet containing the necessary protein sources should be formulated by a nutritionist. For most cats with food allergy, avoiding the offending food is most effective and can result in complete resolution of signs. However, short-term steroid therapy can decrease the concurrent intestinal inflammation until the appropriate food sources can be identified.

GI disease may decrease the availability of a number of micronutrients, such as vitamins and minerals, thereby having important consequences on the pathogenesis, diagnosis, and treatment of the disease. The diagnostic utility of measuring the serum concentrations of cobalamin and folate in cats with suspected intestinal disease has recently been established. Although the impact of deficiencies in cobalamin and folate are not completely known, the role of cobalamin in normal function of the GI tract and in many other aspects of metabolism is well documented. (See "Cobalamin Homeostasis" on page 5) Furthermore, because cats are obligate carnivores that consume much higher amounts of protein in their diet, the importance of cobalamin and other B vitamins in maintaining protein metabolism cannot be overstated. Therefore, evaluation of all cats with GI disease, not just cats with IBD, is an important part of not only the diagnostic process but also the management of these diseases.

Although other vitamin or mineral deficiencies may occur with longstanding or severe IBD, they are less likely (because of storage of fat-soluble vitamins and some minerals), and supplementation without documentation of a deficiency can be dangerous. Thus supplementation of fat-soluble vitamins is not generally recommended unless signs of deficiency, such as bleeding from vitamin K deficiency, are occurring or tissue or blood levels of the vitamin are determined.

Closing remarks

In conclusion, much remains to be learned about the complex interplay between GI microflora, dietary antigens, the epithelium, immune effector cells, and soluble mediators in the feline GI tract in health and disease. The development of feline-specific reagents together with the growing realization of the nutritional consequences of IBD have precipitated a shift beyond reliance on qualitative histology, holding promise for improved understanding, therapy, and prevention in the future.

Debra L. Zoran, DVM, PhD, DACVIM-SAIM

College of Veterinary Medicine and Biomedical Sciences

Texas A&M University

College Station, Texas


1. Dennis JS, Kruger JM, Mullaney TP. Lymphocytic plasmacytic gastroenteritis in cats: 14 cases (1985-1990). JAVMA 1992;200:1712-1718.

2. Hart JR, Shaker E, Patnaik AK, et al. Lymphocytic plasmacytic enterocolitis in cats: 60 cases (1988-1990). JAAHA 1994;30:505-514.

3. Jergens AE, Moore FM, Hayness JS, et al. Idiopathic inflammatory bowel disease in dogs and cats: 84 cases (1987-1990). JAVMA 1992;200:1603-1608.

4. Simpson KW, Fyfe J, Cornetta A, et al. Subnormal concentrations of serum cobalamin (vitamin B12) in cats with gastrointestinal disease. J Vet Intern Med 2001;15:26-32.

5. Day MJ, Bilzer T, Mansell J, et al. Histopathological standards for the diagnosis of gastrointestinal inflammation in endoscopic biopsy samples of the dog and cat: A report from the World Small Animal Veterinary Association Gastrointestinal Standardization Group. J Comp Pathol 2008;138:1-43.

6. Ritchie L. Molecular characterization of intestinal bacteria in healthy cats and cats with IBD. MS dissertation. Texas A&M University, 2008.

7. Goldstein RE, Greiter-Wilke A, McDonough SP, Simpson KW. Quantitative evaluation of inflammatory and immune responses in cats with inflammatory bowel disease. Am Coll Vet Intern Med Proc, 2003.

8. Waly NE, Stokes CR, Gruffydd-Jones TJ, et al. Immune cell populations in the duodenal mucosa of cats with inflammatory bowel disease. J Vet Intern Med 2004;18:113-122.

9. Inness VL, McCartney AL, Khoo C, et al.Molecular characterisation of the gut microflora of healthy and inflammatory bowel disease cats using fluorescence in situ hybridisation with special reference to Desulfovibrio spp. J Anim Phys Anim Nutr 2006;91:48-53.

10. Van Nguyen N, Tagliner K, Helps CR, et al. Measurement of cytokine mRNA expression in intestinal biopsies of cats with inflammatory enteropathy using quantitative real-time RT-PCR. Vet Immunol Immunopathol 2006;113:404-414.

11. Janeczko S, Atwater D, Bogel E, et al. The relationship of mucosal bacteria to duodenal histopathology, cytokine mRNA, and clinical disease activity in cats with inflammatory bowel disease. Vet Microbiol 2008;128:178-193.

12. Jergens AE. Inflammatory bowel disease. Current perspectives. Vet Clin North Am Small Anim Pract 1999;29:501-521.

13. Weiss DJ, Gagne JM, Armstrong PJ. Relationship between inflammatory hepatic disease and inflammatory bowel disease, pancreatitis and nephritis in cats. JAVMA 1996;209:114-116.

14. Banks C, Bateman A, Payne R, et al. Chemokine expression in IBD: Mucosal chemokine expression is unselectively increased in both ulcerative colitis and Crohn's disease. J Pathol 2003;199:28-35.

15. Cario E. Bacterial interactions with cells of the intestinal mucosa: Tolllike receptors and NOD2. Gut 2005;54:1182-1193.

16. Elson CO, Cong Y, McCracken VJ, et al. Experimental models of inflammatory bowel disease reveal innate, adaptive, and regulatory mechanisms of host dialogue with the microbiota. Immunol Rev 2005;206:260-276.

17. Hanauer SB. Inflammatory bowel disease: Epidemiology, pathogenesis, and therapeutic opportunities. Inflam Bowel Dis 2006;12(Suppl 1):S3-S9.

18. Haller D, Holt L, Parlesak A, et al. Differential effect of immune cells on non-pathogenic gram-negative bacteria-induced nuclear factor-kappaB activation and pro-inflammatory gene expression in intestinal epithelial cells. Immunology 2004;112:310–320.

19. Guarner F. Probiotics in gastrointestinal diseases. In Versalovic J, Wilson M (eds): Therapeutic Microbiology: Probiotics and Related Strategies —Washington, DC: ASM Press, 2008, pp 255-271.

20. Trepanier L. Idiopathic inflammatory bowel disease in cats: Rational treatment selection. J Feline Med Surg 2009;11:32- 38.

21. German AJ. Inflammatory bowel disease. In Bonagura J, Twedt D (eds): Kirk's Current Veterinary Therapy XIV—St. Louis, MO: Saunders/Elsevier, 2008, pp 501-506.

22. Westermarch E. Tylosin responsive diarrhea. In Bonagura J, Twedt D (eds): Kirk's Current Veterinary Therapy XIV—St. Louis, MO: Saunders/Elsevier, 2008, pp 507-509.

23. Veir JK, Knorr R, Cavadini C, et al. Effect of supplementation with Enterococcus faecium (SF68) on immune functions in cats. Vet Ther 2007;8:229-238.

24. Guilford WG, Strombeck DR, Rogers Q, et al. Food sensitivity in cats with chronic idiopathic gastrointestinal problems. J Vet Intern Med 2001;15:7-13.

25. Guilford WG, Center SA, Strombeck DR, et al. Dietary therapy of feline diarrhea. NZ Vet 2003;51:262-265.

26. Roudebush P. Adverse reactions to foods: Allergies versus intolerance. In Ettinger SJ, Feldman EC (eds): Textbook of Veterinary Internal Medicine, ed 6—St. Louis, MO: Elsevier, 2005, p 153.

27. Verlinden A, Hesta M, Millet S, et al.Food allergy in dogs and cats: A review. Crit Rev Food Sci Nutr 2006;46:259-273.

28. Laflamme DP, Martineau B, Jones W, et al. Evaluation of two diets in the nutritional management of cats with naturally occurring chronic diarrhea. Vet Ther 2004;5:43-51.

Are Bacteria a Key Component?

One group of investigators1 is seeking to determine the effect of mucosal bacteria and their relationship to cytokine responses and inflammation in the bowels of cats. Intestinal biopsies were collected from 17 cats undergoing diagnostic investigation of signs of GI disease and from 10 healthy controls.1 Subjective duodenal histopathology ranged from normal (10) to mild (6) to moderate (8) to severe (3) IBD. The mucosal response was evaluated by objective histopathology and cytokine mRNA levels in duodenal biopsies. The number of mucosa-associated Enterobacteriaceae was higher in cats with signs of GI disease than in healthy cats. These pathogens, including Escherichia coli and Clostridium species, were associated with significant changes in mucosal architecture, principally atrophy and fusion; up-regulation of cytokines, particularly IL-8; and the number of clinical signs exhibited by affected cats.

The study findings indicate that an abnormal mucosa-associated flora is associated with the presence and severity of duodenal inflammation and clinical disease activity in cats. The observations provide a rational basis for future investigations to address the potential causal involvement of mucosa-associated bacteria. They are perhaps most consistent with a model proposed for the mucosal response to gram-negative bacteria, whereby proinflammatory cytokines (e.g. IL-1, IL-8, IL-12) produced by epithelial cells in response to such stimuli as gram-negative bacteria are modulated by macrophage production of IL-10. Support for this concept in the canine GI tract is provided by studies of the small intestines of dogs in which expression of IL-10 and IFN-β mRNA by lamina propria cells and the intestinal epithelium was observed in the face of a luminal bacterial flora that was more numerous than that of control dogs.2

Additional evidence that bacteria are a key component of IBD in cats has been collaborated by Inness and coworkers,3 who characterized the gut microflora of both healthy cats and cats with colonic IBD. Cats with IBD were found to have significantly higher populations of Desulfovibrio (a genus of bacteria that produce toxic sulfides) compared with normal cats, which had higher populations of bifidobacteria and bacteroides (normal flora). These authors proposed that modulation of intestinal flora with probiotics and dietary intervention to decrease the production of pathogenic bacteria were likely important in treating cats with IBD.

Finally, another study4 found that the expression of cytokines in biopsy specimens from the intestines of cats with IBD represented greater transcription of genes encoding IL-6, IL-10, IL-12, TNF-α, and TGF-β than from those of cats with normal intestines. These results also suggested that, in cats with IBD, both proinflammatory and immune dysregulation features were present.

IBD = inflammatory bowel disease; IFN = interferon; IL = interleukin; TGF = transforming growth factor; TNF = tumor necrosis factor


1. Janeczko S, Atwater D, Bogel E, et al. The relationship of mucosal bacteria to duodenal histopathology, cytokine mRNA, and clinical disease activity in cats with inflammatory bowel disease. Vet Microbiol 2008;128:178-193.

2. Jergens AE, Sonea IM, Kauffman LK, et al. Intestinal cytokine mRNA expression in canine inflammatory bowel disease: A meta-analysis with critical appraisal. Comp Med 2009;59:153-162.

3. Inness VL, McCartney AL, Khoo C, et al. Molecular characterisation of the gut microflora of healthy and inflammatory bowel disease cats using fluorescence in situ hybridisation with special reference to Desulfovibrio spp. J Anim Phys Anim Nutr 2006;91:48-53.

4. Tagliner K, Helps CR, et al. Measurement of cytokine mRNA expression in intestinal biopsies of cats with inflammatory enteropathy using quantitative real-time RT-PCR. Van Nguyen N, Vet Immunol Immunopathol 2006;113:404-414.

Diets Designed to Promote GI Health

The highly digestible diets from different pet food manufacturers have a variety of formulations—different protein and carbohydrate sources, different levels of fat, and various additives designed to promote intestinal health (e.g. fructooligosaccharide [FOS], mannondigosaccharide [MOS], omega-3 fatty acids, antioxidant vitamins, soluble fiber). If one type of highly digestible diet has been fed for at least two weeks with minimal response, then it is entirely reasonable to try another diet from a different source or try an entirely different dietary strategy (e.g. high-protein/low-carbohydrate, novel antigen, hydrolyzed diet). In addition, diarrhea may be attributed to carbohydrate intolerance or bacterial changes resulting from dietary changes. Thus, the addition of probiotics or prebiotics to help influence microflora is a reasonable therapeutic option as well as the addition of either metronidazole or tylosin.

Cobalamin Homeostasis

Cobalamin homeostasis is a complex, multistep process that involves participation of the stomach, pancreas, intestines, and liver. Following ingestion, cobalamin is released from food in the stomach. It is then bound to a nonspecific cobalamin-binding protein of salivary and gastric origin called haptocorrin. IF, a cobalamin-binding protein that promotes cobalamin absorption in the ileum, is produced by the stomach and pancreas in dogs and the pancreas but not the stomach in cats.1

The affinity of cobalamin for haptocorrin is higher at acid pH than that for IF, so most is bound to haptocorrin in the stomach. After entering the duodenum, haptocorrin is degraded by pancreatic proteases and cobalamin is transferred from haptocorrin to IF.1

A portion of cobalamin taken up by hepatocytes is rapidly re-excreted in bile bound to haptocorrin. This rapid turnover means that cats with cobalamin malabsorption can totally deplete their body cobalamin stores within one to two months.1

Recent studies indicate that subnormal cobalamin concentrations are common in cats with GI disease or exocrine pancreatic insufficiency.2 Investigation of the relationship of subnormal serum cobalamin concentrations to cobalamin deficiency and the effect of cobalamin deficiency on cats has revealed the clinical significance of cobalamin deficiency in cats.2

Serum MMA concentrations (median; range) decreased after cobalamin supplementation. Serum homocysteine concentrations were not significantly altered, whereas cysteine concentrations increased significantly. Mean body weight increased significantly after cobalamin therapy, and the average body weight gain was 8.2%. Significant linear relationships were observed between alterations in serum MMA and fTLI concentrations and the percentage of body weight change.

There is also emerging evidence that cobalamin supplementation may result in clinical improvement of cats with IBD without recourse to immunosuppressive therapy.3 In this respect, it is interesting to note that cobalamin deficiency is associated with altered immunoglobulin production and cytokine levels in mice. The impact of cobalamin deficiency on the immune environment of cats remains to be established.

fTLI = feline trypsin-like immunoreactivity; IF = intrinsic factor; MMA = methylmalonic acid


1. Ruaux CG, Steiner JM, Williams DA.Early biochemical and clinical responses to cobalamin supplementation in cats with signs of gastrointestinal disease and severe hypocobalaminemia. J Vet Intern Med 2005;19(2):155-160.

2. Subnormal concentrations of serum cobalamin (vitamin B12) in cats with gastrointestinal disease. Simpson KW, Fyfe J, Cornetta A, et al. J Vet Intern Med 2001;15:26-32.

3. Steiner JM. Diagnosis of pancreatitis. Vet Clin North Am Small Anim Pract 2003;33:1181-1195.

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