Peer Reviewed

Nutrition

Nutrition and Feline Idiopathic Constipation

The mainstay of feline idiopathic constipation management is nutrition, including potential modifications to diet form and fiber intake.

December 14, 2021 |

Issue: January/February 2022

Lightspruch/shutterstock.com

Constipation is characterized by prolonged gastrointestinal (GI) transit, associated with dry stool and difficult or absent defecation.¹ Although cats of all ages and both sexes can be affected, middle-aged to older male cats are over-represented.^2-5 Constipation can occur secondary to local GI or systemic diseases (TABLE 1). After predisposing causes are excluded, the diagnosis for an estimated 60% to 70% of cats is idiopathic constipation.¹⁶ Cats with recurrent constipation require lifelong therapy; some with refractory disease need periodic hospitalization or surgical intervention. This article describes the diagnosis and medical management of feline idiopathic constipation, with a focus on nutritional strategies.

Etiology of Feline Constipation

The pathophysiology of feline idiopathic constipation is incompletely understood but is most likely multifactorial; contributing factors include dehydration, GI neuronal signaling, and GI-microbiome interactions. An in vitro study showed that the colonic contractile response to neurotransmitters (e.g., acetylcholine, cholecystokinin, substance P) is less in cats with end-stage disease (i.e., megacolon) than in healthy cats.¹⁷ Studying cats with megacolon limits the ability to interpret whether dysmotility is the underlying cause of disease or secondary to chronic distention. The same study found that decreased contractility was not related to decreased colonic muscle mass and that smooth muscle histopathology was normal.¹⁷

A recent study found that, in cats with constipation of varying severity, GI pacemaker cells (i.e., interstitial cells of Cajal) were decreased, numbers of myenteric neurons were decreased, and myenteric neurons were degenerate.⁴ Together, those findings suggest disordered enteric nervous system stimulation rather than a primary muscular disorder, which enables selection of therapies that could improve response to enteric nervous system signaling.

Additional evidence supports a self-perpetuating process, wherein retained feces become progressively dehydrated as a result of normal colonic water absorption.¹⁸ Recurrent constipation contributes to permanent distention and dysmotility.^2,10,19

Diagnosis of Feline Constipation

History

For cats presented with constipation, a thorough history is critical. History enables assessment of disease severity and identification of environmental and diet factors that can be targeted therapeutically. Key questions include duration of signs, frequency of constipation episodes, time of last defecation, and stool volume during defecation. Fecal scoring²⁰ can be used to define stool consistency at presentation and to gauge therapeutic response. BOX 1 lists clinical signs reported in cats with constipation as well as less common signs related to GI mucosal irritation or marked tenesmus (e.g., vomiting). Key environmental questions include litter box accessibility and hygiene, difficulty getting into the litter box, and water sources (e.g., types and accessibility). Diet history should include diet form (i.e., dry versus canned), amount fed, feeding frequency, specific diet (including protein and carbohydrate sources), recent diet changes, and any treats or supplements.

BOX 1 Clinical Signs of Idiopathic Constipation in Cats^{2,5,7,15,18,21}

Commonly Observed

Abdominal pain
Decreased to absent defecation
Hyporexia
Lethargy
Small, dry feces
Tenesmus

Less Commonly Observed

Hematochezia
Intermittent diarrhea
Vocalization during defecation
Vomiting

Examination

Abdominal palpation of constipated cats reliably detects a colon distended with firm feces. Other findings can include dehydration, abdominal pain, and weight loss associated with either decreased food intake or predisposing chronic disease.^2,21 Complete orthopedic and neurologic examinations are indicated to evaluate for pain, focal neurologic deficits, or generalized autonomic dysfunction. Digital rectal examination rules out rectal stricture and secondary perineal hernia but for most cats requires sedation or general anesthesia.

Diagnostic Tests for Feline Constipation

All cats with constipation should undergo abdominal radiography to determine severity and rule out predisposing anatomic factors. Radiographic constipation is defined as a maximum colonic diameter >1.3 times the length of the fifth lumbar vertebral body.²² Ratios of >1.48 have been associated with radiographic megacolon and >1.62 with medical management failure (i.e., need for subtotal colectomy).²² Note, however, that a single radiograph can diagnose only existing constipation, not clinical obstipation or megacolon. Clinical obstipation implies a loss of functional reserve, and diagnosis is based on lack of treatment response. Megacolon is a descriptive term for end-stage disease associated with permanent dilation and motility loss.^7,16 Treatment recommendations should be based on serial clinical observations.

Although a minimum database (complete blood count, serum chemistry profile, urinalysis) does not establish the diagnosis of constipation, one can be used to identify predisposing metabolic causes and objectively assess hydration status. When hypothyroidism is suspected, total thyroxine and thyroid-stimulating hormone concentrations should be measured.

Therapeutic Approaches for Feline Constipation

Immediate treatment of severe constipation is aimed at resolving dehydration and promoting evacuation of fecal material. Strategies include combinations of intravenous fluids, enteral (nasogastric) water or osmotic electrolyte solutions, lactulose, enemas, and manual deobstipation.^1,7,22 Before performing manual deobstipation, dehydration should be corrected and attempts should be made to aid fecal passage via enteral or enema-administered osmotic agents; most cats administered the aforementioned treatment will defecate without the need for manual deobstipation.^2,23 After the acute episode has been corrected, the next focus should be preventing recurrence, and the mainstay of management is nutrition.

Dietary Intervention/Management for Feline Constipation

Diet Form

Regardless of diet form, cats with recurrent constipation should have free-choice, unobstructed access to fresh water, and strategies should be used to increase water intake.²⁴ Historically, canned food has been recommended. However, a recent study found no difference in diet form between cats presented to an emergency room for constipation versus other diseases,² but that study did not control for other diet factors (e.g., macronutrient content, specifically fiber) or factors affecting hydration. Because many cats requiring in-hospital management of constipation are dehydrated and treatments for chronic feline constipation increase needed water intake, the author still recommends a canned diet. In cats unwilling to eat a canned diet, water can be added to kibble, which increases dietary water content and subsequently fecal water content.²⁵ It can also be helpful to try foods of different textures (e.g., paté versus morsels with gravy).

Fiber Content for Feline Constipation

The most common macronutrient manipulated in cats with idiopathic constipation is fiber. Broad recommendations tend to focus on high-fiber versus low-fiber diets; however, this approach is oversimplified. Different fibers play distinctive roles in constipation management. Unfortunately, few prospective studies have evaluated fiber type in cats with chronic constipation; therefore, most historical recommendations are based on expert opinion, in vivo studies in healthy cats, or extrapolated from in vitro effects on fecal material or intestinal mucosa of healthy cats or dogs. The different types of diets for cats with chronic constipation are those with low-solubility/insoluble nonfermentable fibers, moderate-to-high solubility fibers with varying fermentability, and low residue/low fiber.

Low-solubility to insoluble nonfermentable fibers (e.g., cellulose, wheat bran) act as bulking agents. Insoluble fiber promotes motility by direct colonic distention and may benefit cats with constipation but without clinical obstipation/megacolon. In cats with loss of colonic function, diets high in insoluble fiber may worsen clinical signs by increasing fecal content in those with ineffective peristalsis. Diets high in insoluble fiber also decrease fecal moisture;²⁶ therefore, it is crucial that cats fed these diets consume adequate water.
Moderate-to-high solubility fibers help retain water within the colon but may still increase bulk, depending on not only solubility but also fermentability. Fermentability describes the extent of fiber metabolization by GI bacteria to by-products, such as short-chain fatty acids (SCFAs).Psyllium is a soluble, nonfermentable fiber that forms a mucilaginous gel within the colon and is a common fiber source in commercial foods. Although fiber sources in this category increase fecal bulk and should be used cautiously in cats with severely decreased motility, they also promote colonic water retention, which helps mitigate absorptive water loss. One study showed that a psyllium-containing diet improved chronic constipation in cats, completely resolving clinical signs for 82% to 93%.²¹ However, the observed effect cannot be attributed to psyllium alone because the diet fed in that study contained other fiber sources (chicory pulp) and additives (fructooligosaccharides, mannan-oligosaccharides), which have been shown to affect fecal SCFAs.In vitro studies using soluble, fermentable fibers (e.g., many pectins, gums, inulin) have demonstrated increased fecal SCFAs^27-29 and support the role of SCFAs in promoting colonic motility in cats.³⁰ Highly fermentable fibers also increase fecal water content via osmotic pull.^28,31
Many commercial foods contain a mixture of insoluble and soluble, fermentable fibers (e.g., beet pulp). Findings of several in vitro studies suggest that a moderately soluble and fermentable fiber profile may result in the best fecal environment (e.g., pH, water content, SCFA profile).^27-29,32,33 A mixed-fiber profile increases fecal volume and water content. A study of cats with constipation but not clinical megacolon found that a mixed-fiber diet improved signs in all cats within 1 month.³⁴
Low-residue diets are low in fiber and contain highly digestible proteins, fats, and carbohydrates (>87% to 90%), leading to decreased fecal bulk. These diets may benefit cats with severely decreased colonic motility; however, prospective studies of low-residue diets in cats with clinical obstipation/megacolon are lacking.

In addition to being included in a commercial diet, fiber can be supplemented independently. For example, unflavored psyllium powder can be added to a low-residue diet at a recommended dose of 1 to 4 teaspoons twice daily.⁷ To the author’s knowledge, no studies have compared fiber-supplemented versus low-residue diets in cats with chronic constipation; multiple diet trials may be needed.

Supplements and Ancillary Medications for Feline Constipation

Treatment for feline idiopathic constipation is often multimodal, including many drugs and supplements (TABLE 2) in addition to dietary management. These supplements often target either improved (i.e., less firm) stool consistency or increased colonic contractility. For many cats, an osmotic laxative combined with a promotility medication with actions on colonic contractility can be effective. In vivo evidence supports efficacy of osmotic laxatives in cats with constipation.^35,36 Promotility drugs appear safe³⁸ and have in vivo efficacy for other GI motility disorders in cats³⁹ as well as in vitro evidence for stimulation of colonic motility.^17,37 These medications are typically added when rehydration and diet modification alone are not sufficient to control clinical signs. However, maintaining hydration is still critical when ancillary medications, particularly laxatives, are added. Although more studies are needed, newer therapies targeting the GI microbiome to achieve improved fecal consistency in healthy cats (e.g., prebiotics^28,29,32,33) and cats with chronic constipation (e.g., probiotics⁴) are promising. Because the effects of various prebiotics and probiotics are not interchangeable, evidence for use cannot be extrapolated to other bacterial strains or products.

Take-Home Points

Dietary management is key to long-term therapy in cats with chronic idiopathic constipation.
Fiber is the most promising macronutrient for improving chronic idiopathic constipation. Individual cats may benefit from different combinations of soluble versus insoluble and fermentable versus nonfermentable fibers.
Distinguishing between radiographic versus clinical obstipation/megacolon may affect choice of the most beneficial diet for an individual cat.
Because fiber supplementation and ancillary medications (e.g., osmotic laxatives) can increase water needs, adequate water intake should be ensured.
Treatment of chronic feline constipation requires an individualized approach, with periodic monitoring and adjustment of diet strategies and ancillary therapies, depending on the cat’s response.