Flatulence: Causes and Management Options

Hill's Science and TechnologyCenterTopeka, Kansas

Philip Roudebush, DVM, DACVIM

ABSTRACT: Flatulence is defined as excessive formation of gases in the stomach or intestine. It is usually associated with noticeable flatus, belching, borborygmus, abdominal distention, or a combination of these signs. Excessive aerophagia is a risk factor for flatulence and is noted commonly in brachycephalic, working, and sporting breeds as well as in dogs with aggressive or competitive eating behaviors. The primary goal of dietary management of flatulence is to reduce the gas formation that results from bacterial fermentation of intestinal substrates.

Flatuience-excessive formation of gases in the stomach or intestine-is usually associated with noticeable flatus, belching, borborygmus, abdominal distention, or a combination of these signs. Flatus, rather than flatulence, is the term that should be used for gas expelled through the anus. Belching is the noisy voiding of gas from the stomach through the mouth, and borborygmus is a rumbling or gurgling noise caused by propulsion of gas through the intestines.

Excessive flatus is a chronic, objectionable problem that is common in dogs but less so in cats. Although belching, borborygmus, and abdominal distention are less common signs, pet owners may mention them if asked specifically about them. Flatus, belching, and borborygmus occur in healthy pets but may also develop as a consequence of gastric, small intestinal, or colonic disorders.

       Production Of Intestinal Gas

The tendency to treat flatus as a humorous topic has obscured appreciation of the complex physiology that underlies the formation of intestinal gas. The quanti­tatively important gases in the intestinal tract are nitrogen (N_Z), oxygen (O_Z), hydrogen (Hz), carbon dioxide (CO,), and methane (CH4).'-4 These odorless gases make up more than 99% of the intestinal gas volume in humans and pets (Table 1). The characteristic unpleasant odor of intestinal gas arises primarily from the trace gases that contain volatile sulfur compounds such as hydrogen sulfide, methanethiol, and dimethylsulfide. The noxious odor of flatus in both humans and dogs correlates most strongly with the concentration of hydrogen sulfide.

Gas occurs naturally in the gastrointestinal (GI) tract and primarily results from the following four events:

Gases can be removed from the gut through passage from the esophagus or anus, diffusion into the blood, or consumption by bacteria. The net of these processes near a given site in the GI tract determines the volume and composition of gas passing that site.

Gas in the digestive tract is believed to result primarily from aerophagia, during which air enters the stomach during swallowing of liquids or solids. Studies using ultrafast computed tomography in humans show that a mean of 17 ml of air accompanies the swallowing of 10 ml of water. Given the quantity of food and fluid ingested each day, large amounts of air may normally enter the stomach. If not belched, the N, component of swallowed air passes through the GI tract with minimal absorption and is then passed per rectum. Air can also be swallowed in the absence of food or water ingestion through the propulsion of a bolus of air into the pharynx. This can cause the excessive flatus commonly seen in many brachycephalic breeds. Vigorous exercise and rapid and competitive eating situations may exacerbate aerophagia. Intestinal transit time is considerably shorter for gases than for liquids or solids. Air introduced into the stomach can result in flatus within 15 to 35 minutes. It has been estimated that gases can move 10 cm/sec through the GI tract.

The interaction between hydrochloric acid and alkaline food, saliva, or bicarbonate secreted by the pancreas produces CO, in the stomach and intestines. CO, also enters the GI tract through diffusion from the blood. Belched gas is largely swallowed air plus variable quantities of CO.

A large amount of gas is formed from bacterial fermentation in the colon. Substrates for bacterial gas production include dietary substances (e.g., fiber, poorly digestible protein, carbohydrates) and endogenous sources (e.g., mucin, bile acids). Foods that contain large amounts of nonabsorbable oligosaccharides (e.g., raffinose, stachyose, verbacose) are likely to produce large amounts of intestinal gas. Dogs and cats lack the digestive enzymes needed to split these sugars into absorbable monosaccharides. Therefore, bacteria in the colon rapidly ferment these sugars, producing H, and CO, Soybeans, beans, peas, and other legumes contain large quantities of nonabsorbable oligosaccharides and are often associated with excessive flatus. Many fibers used in pet foods are fermented by colonic microflora and may contribute directly to flatus. Rapidly fermentable fibers in pet foods include pectins and most gums. Fiber­containing foods may contribute to flatus indirectly through reduced dry-matter digestibility Intestinal gas production is also increased by fresh or dried foods containing fructose, resistant starches, and fermentable fiber (e.g., apples, grapes, prunes, raisins, bananas).

Diseases that cause maldigestion or malabsorption are often associated with borborygmus, abdominal distention, and excessive flatus because large amounts of nonassimilated substrates are available for bacterial fermentation. Flatus is also common in adult dogs and cats fed excessive amounts of lactose-containing foods.

Sulfur-containing gases are the major malodorous components of human and canine flatus." Dietary sources of sulfur (sulfates and sulfur-containing amino acids) and endogenous sulfur-containing compounds (e.g., mucin, taurocholate) are converted by sulfate­reducing bacteria to the odoriferous compounds hydrogen sulfide, methanethiol, and dimethylsulfide." Onions, nuts, spices, cruciferous vegetables (e.g., broccoli, cabbage, cauliflower, brussels sprouts) and carrageenan contain high levels of sulfate and often increase production of malodorous gases; high-protein ingredients may also contribute to production of such gases.

Patient Assessment

Pet owners often express concerns with clinical manifestations of flatulence and may describe an increase in frequency of belching, flatus or borborygmus, objectionable odor of flatus, or abdominal distention. In one study, 47 of 110 dog owners (43%) reported flatus in their otherwise-healthy dogs and 14 owners (13%) reported objectionable odor associated with the flatus episodes. Dogs housed indoors and less active dogs were more likely to have evidence of flatus. Temperament, frequency of feeding, specific diet, eating habits, age, gender, and history of previous GI disease were not found to be risk factors for flatulence in this particular study.

A history of dietary change or dietary indiscretion may be associated with the flatulence. Specific foods, primary food ingredients, treats, supplements, and opportunities for dietary indiscretion should be evaluated. A thorough assessment should also include verification of the current feeding method. Factors to consider include feeding frequency, amount fed, how food is offered, access to other food, relationship of feeding to exercise, and who feeds the animal.

There is widespread belief that some individuals are consistently more flatulent than others. Studies in humans have shown great variability in the frequency of flatus, and such variation probably occurs in animals as well.  Rectal gas excretion rates in humans range from 400 to 1500 ml/day (mean 705 ml/day). Humans, eating their usual diet, passed gas per rectum an average of 8 to 10 times per day with an upper normal limit of 20 times per day. In general, frequency of flatus correlates with the volume of intestinal gas; thus increases and decreases in episodes of flatus can be used to obtain a relative idea of changes in intestinal gas volume. Studies of rectal gas excretion rates in pets whose owners complain of flatus have not been conducted.

Occasionally, belching, abdominal distention, and flatus develop in conjunction with other GI signs, including weight loss, diarrhea, and steatorrhea. This history is very suggestive of an underlying small intestinal disorder. Examples of chronic intestinal disorders often associated with flatulence include exocrine pancreatic insufficiency, inflammatory bowel disease, small intestinal bacterial overgrowth, wheat­sensitive enteropathy, food sensitivity, and lymphang­iectasia. In one study, 18 of 70 cats (26%) with chronic diarrhea and/or vomiting had flatus and 8 cats (11 %) had abdominal distention.` Cats with clinical evidence of flatulence should always be closely evaluated for underlying chronic GI problems such as inflammatory bowel disease or food sensitivity.

Excessive aerophagia is a risk factor for flatulence and is seen with brachycephalic, working, and sporting dogs as well as those with aggressive and competitive eating

behaviors. Dietary indiscretion and ingestion of certain pet food ingredients may be risk factors for some individual animals. Excessive belching, rapid eating, and aerophagia have also been identified as risk factors for gastric dilatation-volvulus and should be considered important clinical findings in dogs at risk for this disorder.

In most cases, physical examination findings in dogs and cats with flatulence are unremarkable. Intestinal gas can often be detected during abdominal palpation, but assessing the quantity of gas from palpation alone is difficult. Laboratory testing is usually not indicated. Animals may be in poor body condition if objectionable flatus is secondary to an underlying GI condition. Further evaluation is in order if vomiting, diarrhea, or weight loss are also present.

Feeding Plans For Patients With Flatulence

Dietary management of flatulence is primarily concerned with decreasing the intestinal gas that results from bacterial fermentation of undigested food (Table 2). Animals with excessive or objectionable flatus generally benefit from highly digestible foods (dry­matter digestibility >90%) offered in small, frequent meals. This protocol reduces the food residues available for bacterial fermentation in the large intestine and should reduce gas production.

Certain protein, carbohydrate, and fiber ingredients or levels may affect flatus production in individual animals. Of the numerous foods alleged to enhance flatus in humans, baked beans are the only natural food that has been carefully studied. A diet deriving half of its calories from baked beans increased flatus in humans from a basal level of 15 to 176 ml/hour. Flatulent animals may benefit from eating foods that do not contain sources of legumes (e.g., soybean meal, soybean mill run, soy hulls, peas, pea fiber, pinto beans).

Changing the source of dietary protein or carbohy­drates may benefit some flatulent animals. In general, aerophagia and dietary carbohydrate are the primary contributors to the volume of intestinal gas, whereas dietary protein contributes to the odoriferous gases. Reports have confirmed that a diet in which all carbohydrates are supplied by white rice reduces intestinal gas formation in humans.^2°2' Studies²²²¹ in dogs also suggest that less intestinal gas is produced when the primary source of carbohydrates is rice than when it is other sources of carbohydrate such as wheat or corn (Figure 1).²³ Therefore, suggesting the use of commercial or homemade foods containing rice as the primary or only source of carbohydrate for flatulent dogs and cats is a prudent recommendation (Table 3).

For example, changing from a commercial dry food that contains corn, chicken meal, and soybean meal to a dry food that contains lamb meal, rice, and barley may be helpful.

Vegetable-based foods containing strongly flavored, sulfur-containing vegetables or legumes should be avoided in flatulent patients. In some cases, reducing dietary protein content alleviates odoriferous flatus. In

most cases, vitamin-mineral supplements should be avoided because these products can alter intestinal microbial activity. Because lactose in food and treats (e.g., cheese, ice cream, milk) may contribute to flatulence in adult animals, foods containing lactose should be eliminated from the diet. Foods that are high in fructose, resistant starch, and/or fermentable fiber should also be avoided. A series of dietary trials is often

successful in finding a food that reduces excessive flatulence or objectionable flatus in individual pets.

Reducing aerophagia is important to control flatulence in dogs, especially brachycephalic breeds. Several small meals should be given daily to discourage rapid eating and gulping of air. Feeding in a quiet, isolated location eliminates competitive eating and reduces aerophagia. These same feeding methods plus feeding a mixture of moist and dry foods may be helpful in reducing the risk of gastric dilatation-volvulus in dogs. Surgical correction of stenotic nares and overlong soft palates may help reduce aerophagia in some brachycephalic dogs.

Simple changes to feeding routines may also reduce objectionable flatus. If possible, dogs should be walked outdoors within 30 minutes of meals. This encourages defecation and elimination of intestinal gas. Less active dogs are at higher risk for objectionable flatus.

MEDICAL THERAPY

Carminatives are medicines or preparations that relieve flatulence. Various herbal and botanical preparations have been used for thousands of years as carminatives. More recently, commercial products have been introduced that claim to reduce or control flatulence. Such products include activated charcoal, bismuth subsalicylate, zinc acetate, simethicone, Yucca schidigera preparations, a-galactosidase, and pancreatic enzyme supplements; these products can be used in conjunction with an altered feeding plan. Nonabsorbable antibiotics, such as neomycin, have also been shown to reduce flatulence and the number of flatus episodes in healthy humans and dogs. However, routine use of nonabsorbable antibiotics in otherwise-healthy pet animals with flatulence is not indicated.

Dry activated charcoal adsorbs virtually all odoriferous gases when mixed directly with human feces and flatus gas. However, ingestion of activated charcoal in humans has not been effective in reducing the number of flatus events, volume of released intestinal gas, fecal odor, or breath H_Z excretion after bean ingestion.  In vitro studies suggest that ingested charcoal fails to reduce liberation of volatile sulfur compounds because of saturation of charcoal binding sites during passage through the gut. Wetting activated charcoal can slow uptake of sulfur-containing gases considerably. Activated charcoal is found in several commercial canine treats purported to control flatulence.

Bismuth subsalicylate (BSS) reduces the odor of feces and flatus in humans when taken frequently (four times daily). Bismuth is the active ingredient and avidly adsorbs hydrogen sulfide, forming insoluble bismuth sulfide. Bismuth sulfide imparts a charac­teristic black color to feces. Bismuth also has antibac­terial activity, which may account for some of the effects. BSS contains 50% bismuth by weight and is found in various commercial veterinary antidiarrheal­adsorbent products as well as in over-the-counter antidiarrheal products for human use (e.g., Pepto­Bismol^°, Procter and Gamble, Cincinnati, OH). There appears to be a striking dose-dependent response with BSS: 400 mg/ 100 g of dry food completely suppresses cecal hydrogen sulfide release in rats, whereas one fifth of this concentration has no demonstrable effect . This agent may be effective in controlling objectionable flatus in pets but probably needs to be given several times per day, which precludes practical, long-term use. It should be used with caution in cats because of concerns with salicylate toxicosis.

Similar to bismuth, zinc acetate binds sulfhydryl compounds and has also been shown to reduce volatile sulfur compounds when exposed directly to gas from

human flatus. Adding zinc acetate to food (1% total diet) decreased fecal hydrogen sulfide concentrations and improved flatus odor in rats .21 One report showed that an oral treat containing zinc acetate, activated charcoal, and Y. schidigera extract reduced highly odoriferous episodes of flatus in dogs.

Simethicone (dimethylpolysiloxane) is an antifoaming agent that reduces surface tension of gas bubbles and is found in commercial veterinary products and over-the­counter products for human use. The mechanism of effect of simethicone in flatulent patients has not been determined-perhaps the altered gas bubbles are more effectively eliminated. A few controlled trials of simethicone treatment have been conducted in humans. In general, simethicone had no effect on total daily flatus volume, number of flatus episodes, or average volume per flatus event. Simethicone may help reduce gastric accumulation of gas and alleviate upper GI signs. The effectiveness of simethicone in controlling flatulence in pets is unknown, and it would not be expected to control objectionable flatus odors.

Extracts of the Y. schidigera plant have been used to control malodorous feces in animal-waste lagoon systems. The mechanisms of action are poorly understood and may include "binding" of ammonia or alterations in microbial activity. In the United States, yucca preparations are approved only as flavoring agents in pet foods and it is unknown whether they effectively control flatulence or objectionable flatus odors when ingested by pet animals. An oral treat containing Y. schidigera extract, activated charcoal, and zinc acetate reduced highly odoriferous episodes of flatus in dogs."

Products containing a-galactosidase are available as human (Beano^°, AkPharma, Pleasantville, NJ) and veterinary (CurTail", AkPharma) products. These products reduce flatus volume by improving digestion of the nonabsorbable oligosaccharides found in soybeans, beans, peas, and other legumes."' These products would not be expected to improve excessive flatus resulting from other causes (e.g., aerophagia) or to reduce the odor of flatus. Anecdotal reports suggest that these products may be beneficial in some animals.

Pancreatic enzyme supplementation has been shown to decrease abnormal intestinal gas production in dogs with exocrine pancreatic insufficiency. Pancreatic enzyme preparations have also been widely used for bloating and abdominal distention in humans. Because ingestion of these preparations should add little to the enzyme output of the pancreas in otherwise-normal individuals, no solid rationale exists for their use in flatulent patients without pancreatic disease. Nevertheless, a recent study showed that a microencap­sulated pancreatic enzyme preparation significantly reduced postprandial symptoms of bloating and abdominal distention in healthy humans ingesting a high-calorie, high-fat meal. This finding suggests that pancreatic enzyme supplements might benefit some patients with flatulence.

More than 30 herbal and botanical preparations have been listed as carminatives. Grape seed extract containing proanthocyanidins is one botanical preparation that has been shown to alter GI microflora and decrease fecal release of volatile sulfur compounds in human patients. The dosage, safety, and efficacy of this and other botanical preparations in pets with flatulence have not been established.

To date, the best evidence exists for short-term use of BSS, zinc acetate, and nonabsorbable antibiotics as carminatives. Less evidence exists for use of activated charcoal, simethicone, digestive enzyme preparations, yucca extract, and grape seed extract. Changing the feeding plan (food and feeding method), rather than using carminatives, offers the best opportunity for successful long-term management of flatulence in pets.

MONITORING PATIENTS WITH FLATULENCE

Patients should be evaluated for evidence of malassimilation if the feeding methods and ancillary therapy outlined here are not successful in reducing or controlling flatulence. Relapse in animals that have been previously asymptomatic often indicates dietary indiscretion. The prognosis for control of flatulence is good in most cases. However, pet owners should be educated about normal intestinal gas production and not expect complete cessation of flatulence, especially in pets with excessive aerophagia. In some cases, the following advice may still be necessary.After trying empirical therapy for pets with chronic flatulence, sound advice for the client is to always stand upwind from the patient.