Diarrhea... the frequent and repeated passage of watery stool, is always a medical concern when it is present in dogs and cats.  Particularly in small breeds such as the  Schnauzer, Pekingese, Dachshund and Chihuahua where there is little body fluid reserves, and in cats for the same reason, diarrhea calls for immediate veterinary medical assistance.  When vomiting is also present the resulting dehydration, electrolyte (minerals such as sodium, potassium, calcium, etc.) imbalance, blood sugar depletion and increased density of the blood can create circulatory collapse and death.  Infectious agents - bacterial, viral, fungal, protozoal, parasitic infections and drugs and toxins all can be culprits in the creation of diarrhea in dogs and cats. Intussusception (telescoping of the bowel on itself), obstructions and intolerance of materials in the diet are known to cause diarrhea. Pancreatitis...both inflammatory and insufficiency (degeneration) creates a persistent diarrhea.

A Partial List of Causes of Diarrhea In Dogs and Cats Click on a topic below to jump down to it
changes in  food	viruses	antibiotics	garbage	enzyme deficiency
intestinal  parasites	bacteria	toxins	foreign material	neurogenic
	Click on an image below  to view large version in a new window
Diarrhea due to hemorrhagic enteritis	Grass and foreign material in stool	See a normal pancreas and compare to the case below	Mixed feces from a cat	Mixed consistency to dog feces
On the right... is the canine patient described below suffering from pancreatic insufficiency	20 pounds underweight! Normal weight after 2 months of treatment			Some dogs require very specific dietary sources to aid in the control of loose stool.  Soft stool may actually be normal for some dogs.  Diarrhea... the frequent passage of watery stool is never "normal" and can have a wide range of causes.

What is diarrhea and how can it be treated and prevented in dogs and cats?  The topic of canine and feline diarrhea could fill a text book!  All kinds of variables impact intestinal health.  To get started we need to know the proper definition of diarrhea, which is the excessive and frequent evacuation of watery feces, usually indicating gastrointestinal distress or disorder.  The bacterial flora of the bowel is a very complex issue partly because hundreds of different species of bacteria can reside within the intestinal tract.  Simply put, there are two main groups... disease causing bacteria (pathogenic) and beneficial bacteria (non-pathogenic).

Definitions...
Diarrhea... Excessive and frequent evacuation of watery feces, usually indicating gastrointestinal distress or disorder.

Loose Stool... Refers to watery feces with no solid form.  (Loose stool would be classified as "diarrhea" if the passage of stool was frequent or excessive in volume.)

Tenesmus...  A painfully urgent but ineffectual attempt to urinate or defecate.

Constipation...  Difficult, incomplete, or infrequent evacuation of dry hardened feces from the bowels.

Obstipation...  Severe constipation caused by intestinal obstruction.

GI or GIT... Gastro-intestinal or gastro-intestinal tract.  Gastric refers to the stomach and intestinal refers to the entire bowel (both small intestine and large intestine).

Flora...  The bacteria and other microorganisms that normally inhabit a body organ or part.

Foreign Material
Grazing on the grass!   Nearly all dogs will occasionally consume grass.  I disagree with the popular notion that “the dog knows he should vomit so he eats grass to make it happen”.   It’s more likely that when dogs have a stomach or intestinal upset, or a sore or irritated throat, they will seek out grass, leaves, sticks and other fibrous material and consume them apparently out of frustration with that unending throat irritation or stomach ache.  Once ingested, grass and the like are so irritating they can cause bleeding along the entire intestinal tract. You’d vomit, too, if you ate a swath of grass!  Normal dogs eat grass simply because they enjoy the texture, odor and taste of it; so when fresh and damp grass is available they’ll go for it.  Don’t believe popular myths that “grass is good for dogs” because it is in fact highly irritating and totally indigestible for dogs.  Grass has about as much food value for canines as an equal amount of the Sunday newspaper.  Dogs like to chew on nylon, plastic, compressed rawhide, electrical cords, expensive shoes, two-by-fours, rotten bones, wallets, and chair legs for one basic reason… it feels good.  So, rather than thinking "the dog knows he should vomit so he eats grass to make it happen", (which really makes no sense), a dog will consume all sorts of fibrous, rough, non-food materials almost compulsively when the throat or stomach is irritated.  Consuming these foreign substances adds additional stress and irritation to an already upset stomach and the dog then vomits the grass and other stomach contents.  See the column written by Dr. Dunn in the March, 2005 issue of Dog World Magazine which addresses the question of why dogs do some of the odd things they do!

Sudden Changes Of Food
One of the most common causes of diarrhea and (and even mild GI upsets) is the ingestion of a food or substance not ordinarily consumed in the diet.  Sudden changes in the dog or cat diet, such as switching to a different (and even better) brand of food can trigger diarrhea.  The usual reason for this sudden shift to watery, frequent stool passage relates to the imbalance within the GI flora that is triggered by new substrates on which the GI flora grow and reproduce.  Change the "food source" for the intestinal flora and the numbers and combinations of bacteria that were previously living in harmony with one another are now shifted in all sorts of ways.  Gas producing bacteria are called fermentative organisms and these are promoted by grain based (carbohydrate) substances such as corn and barley and wheat.  Putrefactive bacteria do not produce gas as readily as fermentative bacteria and these organisms are promoted by the feeding of meat based products such as chicken, beef, and lamb.

Intestinal Worms and Parasites
Most intestinal worms do not cause true diarrhea unless severe intestinal flora composition is present.  Hookworms and whipworms can actually scar the small intestine over a period of time by attaching to the mucosal lining.  Bleeding can occur and blood loss in hookworm infested dogs is common.  Blood may or may not be noticed visually in the stool.  Whipworms usually cause a mucousy coating to the relatively formed stool.  Roundworms do not attach to the intestine but irritate and can cause obstructive discomfort to the dog.  Intestinal cramping and increased intestinal motility is often observed with less firm stool being passed.  Intestinal parasites such as the protozoa Giardia and some others can cause true diarrhea due to their disruptive effects on the intestinal lining cells when they inhabit and reproduce within the cells.  When they are released from the cells lining the small intestine those cells die and a cascade of ill effects ensue.  Coccidia are common irritants of the small intestine of puppies and kittens.  Usually self-limiting IF the patient is otherwise in good health, a debilitated or malnourished or stressed dog or cat can develop severe diarrhea and gas.  Treatment may be needed in dogs and cats displaying clinically loose stool or diarrhea.

Intestinal parasites that are not worms are single celled organisms such as coccidia and the tiny parasite called Giardia.  Giardia can cause true diarrhea and flatulence and dogs (rarely cats) will lose weight, become dehydrated and even pass blood.  Simple routine fecal flotation of a pet's stool in an animal hospital setting often will fail to reveal these tiny, nearly translucent parasites.  Many veterinarians will send stool to a professional veterinary lab with a "heads up" regarding using special stains for Giardia.  Read more about this intestinal parasite at this page.

Coccidia, single celled organisms that invade the surface cells of the dog and cat small intestine, are very common invaders of puppies and kittens.  Especially serious in any pup or kitten that is weakened by stress, poor appetite or crowed/unsanitary housing conditions, coccidiosis (don't confuse with Coccidioidomycosis) causes intestinal cramps, weight loss, mucoid and often watery, bloody stool.

Viruses
Viral intestinal diseases of dogs and cats run the spectrum of severity... from dangerous and deadly to mild and barely noticed.  We all have heard of parvo in dogs, which is caused by a parvovirus strain that has found a friendly niche in canines. Read more about canine diseases here. It truly is a deadly disease.  Coronavirus, like parvoviruses, can affect a number of species including cats and dogs.  The "Feline Distemper virus" causes severe blood diarrhea in affected cats  due to it's extreme suppression of immune factors and  bone marrow production of white blood cells; the weakened intestine has little defense against bacterial invasion from the gut microflora.  Read more about feline diseases here.

Every veterinarian has examined and treated dogs and cats that suddenly developed signs of loose stool, or diarrhea, or diarrhea and vomiting... the cause of which simply remaining unknown.  For example... a housepet with no access to garbage or contaminated water, that has not been near other animals, has not chewed/swallowed foreign material such as grass or bones, and that has had nothing different in its environment and which suddenly stops eating, passes loose stool, vomits two or three times a day and feels slightly depressed.  The veterinarian rules out all reasonable causes and can find nothing other than a slight fever (near 103°), the diagnosis may very well be "a gastrointestinal virus".  In short, we might consider that the dog or cat "has the flu".  (Do not confuse with Canine Influenza.)  Mild stomach or intestinal viruses of dogs and cats are treated symptomatically, usually without use of antibiotics (which are only effective against bacteria).  These mild intestinal viruses generally resolve within three to four days.  NOTE:  Any dog or cat that is thought to have a mild flu-like virus should be treated most vigorously by a veterinarian if the signs persist, if dehydration occurs, if bloody stool or vomit is produced, if a high fever is present, or if the pet is depressed or in pain.

Bacteria
Bacterially induced diarrhea can be dangerous to dogs and cats two ways.  They physically crowd out normal, non-pathogenic, beneficial bacteria in the gastrointestinal tract and they can often produce toxins in their metabolic waste.  Like a factory spewing toxic fumes, bacterial waste products are often toxic.  Clostridia bacteria are a noted example.  Toxins from certain strains of E.coli are often newsmakers in human medicine and dogs and cats can suffer adversely from some E.coli strains if present in the food or environment.  Salmonella and Campylobacter bacteria, like E.coli and other bacterial species,  can affect people and pets and are considered to have  zoonostic (a disease that can be transmitted from animals to man)  potential.

Toxins
Signs of toxin induced diarrhea in dogs and (rarely) in cats are often similar in appearance to loose stool induced by Parvovirus or Coronavirus infections.  Some toxins, such as insecticides, can cause neurological disorders and diarrhea.  Chemicals and toxins such as lead can lead to loose stool or even severe diarrhea.  The positive diagnosis of a toxin causing diarrhea in dogs and cats can be a challenge and may require samples being sent to a veterinary diagnostic lab for positive identification. Learn more about actual poisons in pets here.

Antibiotic Induced Diarrhea
Antibiotics can and do save countless animal and human lives.  Like nearly anything else, though, occasional adverse effects are incurred by the patient.  The most common adverse effect from orally administered antibiotics is a change in the normal, balance intestinal microflora of bacteria and yeast that usually coexist in a beneficial balance of populations.  Depending upon the antibiotic used, intestinal organism populations can be altered in a fashion that allows certain types of organisms to overgrow and other types to be suppressed or eliminated.  One effect of altered bacterial intestinal flora can be diarrhea.  The doctor will evaluate the patient and disease being treated in the light of the antibiotic induced diarrhea.  The pros and cons of continuing the antibiotic and/or treatment for the diarrhea are considered.  Antibiotic induced diarrhea is not the same as an antibiotic hypersensitivity.  Read about the use and misuse of antibiotics in pets here.

Garbage Ingestion
Given the choice many dogs, and only very few cats, would prefer to consume decaying garbage rather than eat their regular diet.  Something new, organic, odoriferous, and mixed in with the opportunity to dig through the distractions to get at the "good stuff" is irresistible.  Bones such as pork, chicken, or beef that are consumed can and do cause serious intestinal obstructions and perforations requiring immediate surgery to save the dog's life.  Do not be misinformed... even cooked bones can cause serious harm if ingested!  In many situations the consumption of decaying foods will have no adverse effects.  However, depending on the types of bacteria and toxins incorporated into the decaying food (garbage) and the quantity of bacteria/toxin ingested, the dog or cat could experience severe gastrointestinal harm.  Vomiting may occur and eliminate some of the ingesta; once the garbage begins its journey along the intestinal tract, though, it will need to traverse the entire intestinal tract before being eliminated... and the noxious substances can further decompose and spread destructive bacteria, toxins and indigestible physical irritants along the entire tract.

Bloody diarrhea and vomiting are seen often with garbage ingestion.  Hemorrhagic gastroenteritis, especially in small dogs or cats, is a life-threatening condition demanding immediate veterinary care and hospitalization.  Curiously, dogs that discover sources of garbage or decomposing dead wildlife and become sick after eating it, will often return to that source and indulge their innate compulsion to consume these materials.  Ingestion of substances with a high content of salt or sugar, or even lactose from milk, can cause diarrhea in dogs and cats.

Pancreatic Insufficiency and Pancreatitis
Digestive enzymes secreted by the canine pancreas include the following:
LIPASE...breaks down fats to fatty acids and glycerol.  The pancreatic lipase is the animal's only source of protein digesting enzyme
TRYPSIN... breaks down protein after being changed from trypsinogen to trypsin by enterokinase from the small intestine lining
CHYMOTRYPSINOGEN... breaks down protein in the small intestine after being activated to chymotrypsin by trypsin.
PEPTIDASES...break down polypeptide chains to amino acids
AMYLASE... breaks down carbohydrates

Pancreatic insufficiency, more precisely "exocrine pancreatic insufficiency" because the exocrine actions relate specifically the digestive enzymes secreted by this organ.  (Endocrine pancreatic insufficiency relates to the hormonal secretions such as insulin and glucagon... necessary chemicals for blood sugar stabilization.)   A lack of or insufficiency in amount of lipase (fat digesting), amylase (protein digesting) or sucrase which breaks down sugars (sucrose) found in some vegetables and many fruits, and sugar derived from sugar cane, sugar beets, sorghum, molasses or maple sugar. Sucrase is beneficial in helping prevent gastrointestinal problems and discomfort.  The dog in this photo had at one time weighed 76 pounds.  Over a six month period he had persistent loose stool and occasional diarrhea;  the watery stool was passed numerous times a day.  At the time of the diagnosis and surgical exploration to check other causes of bowel disease, the dog weighed forty-six pounds and had almost no body fat.  Supplementation of high quality food allowed for normal absorption of nutrients through the normal intestinal lining and the loose stool cleared up.  The dog gained weight and is now normal, healthy and active.

Pancreatitis is an inflammation of the pancreatic gland which is situated very close to the origin of the small intestine (duodenum) near the pyloric area of the stomach.  This elongated, thin organ has numerous responsibilities including secreting hormones into the bloodstream  such as insulin and glucagon which act in concert to regulate blood sugar levels within rather narrow limits.  As well, life would not be possible for dogs or cats without digestive enzyme production and secretion into the lumen of the intestine.  These digestive enzymes can actually cause the demise of the dog or cat if they leak into pancreatic tissues or surrounding abdominal structures.  Therefore any inflammation of the pancreas has potentially life-threatening consequences.  Pancreatitis can result from trauma, sudden ingestion of fat, toxins, viruses and other unknown causes.  One usual consequence of pancreatitis is diarrhea and vomiting.  Pain is a hallmark of pancreatitis and it is always considered a priority for treatment by attending veterinarians.

Neurogenic
The stool seen in this image was produced by a normal dog that had no intestinal parasites and no evidence of bacterial or viral infection.  The dog was placed in a roomy pen at an animal hospital overnight and was provided water and no food in preparation for a surgical procedure the following day.  Apparently the "stress" of the new environment, possible kennel noises during the night and separation anxiety from missing his owners triggered a hypermotile gastrointestinal tract.  The rapid passing of intestinal material creates stool that did not spend enough time in the large intestine to have the usual fluid reabsorption processes take place.  Since semi-fluid intestinal contents must spend some time in the colon to have fluid reabsorption take place so that firm stool can be passed and rapid transit or early expelling of stool will result in loose feces rather than firm or hard feces.  As in this specimen, even small amounts of blood will occasionally be seen in loose stool of neurogenic origin.  After this dog's neuter procedure and a few meals at home, the dog again passed normal fecal material.  Neurogenic diarrhea or loose stool is seen in dogs that are boarded, suffer from motion sickness or travel stress, are suddenly placed in physically demanding situations or are frightened from storms or strange situations.