Few things are more frightening than seeing blood in the stool because this is sometimes a warning sign of cancer, at least in people. But in dogs and cats, it generally isn't quite that serious, says Michael Brothers, D.V.M., a veterinarian in private practice in Middletown, Connecticut. Still, blood in the stool is not normal; it always means that something is wrong.

Hematochezia is the presence of bright red, fresh blood in the stool or feces. Hematochezia usually occurs with bleeding in the lower intestines (colon, rectum). There is a good chance that something sharp, like a bit of bone scraped the lining of the large intestine and made it bleed. The bleeding may continue for a day or two, but it probably won't last much longer. Even small scrapes can cause a lot of bleeding, so don't be surprised when the stools appear quite red.

Hematochezia should not be confused with Melena which is the passage of old, digested blood making the stools appear black and tarry. Melena may represent a severe, life-threatening illness, and should not be ignored. It must especially be addressed if it persists or worsens. Melena develops when bleeding occurs into the stomach or small intestines. The bleeding must be high in the intestinal tract in order for the blood to be digested and become discolored.

Hematochezia may be a symptom of either a minor problem, or a potentially more serious problem in the animal. One occurrence of hematochezia may be a minor and short lived. However, repeated or persistent hematochezia is more serious and should not be ignored. There are several possible causes. The most common cause in older pets is cancer and in younger pets are parasites. Blood in the stool may also be a sign of parasites, like whipworms, which are irritating the intestine wall.

Some viral infections can temporarily irritate the walls of the small intestine and make it bleed. Blood in the stool can also be a sign of colitis, an inflammation of the large intestine. Also types of food poisoning or other intestinal infections are associated with bleeding. The main bacteria and parasites that can cause bloody diarrhea are Salmonella, Shigella, invasive E. Coli 0157, Campylobacter, Yersinia, and Entaomeba histolytica.

Finally, bleeding may be caused by an infection of the anal sacs -- two sacs on either side of the anus that contain a strong liquid that pets use to mark their territory. These sacs normally empty whenever your pet has a bowel movement. When the sacs are infected, however, they don't empty the way they should, causing them to swell. Having a bowel movement can irritate the area, causing blood to flow.

See Your Vet If...

  • The surface of your pet's stool has spots or smears of blood
     
  • His stool is dark and tarry-looking
     
  • Pushing on your pet's belly causes him pain
     
  • He hasn't eaten for 24 hours or more
     
  • His abdomen appears bloated
     
  • He has eaten rodent poison, antifreeze, houseplants, or other harmful substances
     
  • He has been vomiting for more than a day or is vomiting blood
     
  • There are worms or other parasites in his stool
     
  • He has had diarrhea for 24 hours or more
     
  • There is blood in his stool or it looks dark and tarry
     
  • He is scooting across the floor, or the anal area looks swollen
     
  • He has gained or lost substantial amounts of weight
     
  • He is having side effects from medication, like appetite loss or vomiting
     
  • There are growths in the anal area
     
  • There is a bulge in his throat
     
  • He is drooling much more than usual
     
  • He vomits shortly after eating
     

What You Can Do for Your Pet

There is no reason to panic at the first sign of blood. Even though it looks scary, it usually isn't serious, anymore than a bloody nose is. "If you see just a few specks of red blood, I wouldn't worry about it," says Dr. Brothers. In most cases, the problem will be minor, and the bleeding will stop in a day or two.

In fact, you can often prevent bleeding by taking simple precautions. For starters, skip the bones, says David Tayman, D.V.M., a veterinarian in private practice in Columbia, Maryland. No matter how much your pet loves them, bones generally do more harm than good. As pets crunch them into small bits, the bones often get sharp edges that can damage the intestine. As an alternative, he suggests rawhide bones for dogs. Make sure your pet is supervised while chewing on rawhide bones to see that he is not ingesting large pieces. Or you can buy nylon bones at pet supply stores.

Reducing your pets' exposure to parasites can be very helpful for preventing bleeding. One way to do this is simply to stop your pets from sniffing (or, worse, eating) other pets' stools. "Most parasites are contracted by sniffing the stool of other pets," says Howard Rothstein, D.V.M., a veterinarian in private practice in Saugerties, New York.

It is a good idea to clean the yard after every bowel movement and to scoop out the litter box every time it has been used. "That way they can't reinfect themselves," says Dr. Rothstein.

If you live in the country or go for hikes in the woods with your pet, pack enough water for the day -- for you and him -- since streams and ponds are common sources of parasites. Even stagnant water in your yard, under a rainspout, for example, may harbor parasites.

Even though blood in the stool usually indicates a minor problem, sometimes it is a serious warning sign. Don't take chances if there is a lot of blood or if the stool looks dark and tarry. Take a stool sample when you notice the problem, and make an appointment to see your vet as soon as possible, says Karen Mateyak, D.V.M., a veterinarian in private practice in Brooklyn New York. It's best if the sample is less than 24 hours old at the time of your appointment, she adds.

What Your Vet Can Do 

The appearance of the blood tells a lot about what the problem is, so your vet will ask a lot of questions: Was it bright red or a darker color? Were there just a few drops or a dramatic splash? Did it appear on the surface of the stool or was it mixed up inside?

Your vet will examine the stool sample under a microscope to see if there are parasites. This isn't as easy as it sounds since the only sign of some parasites will be their eggs, which only appear in stools periodically -- the parasites themselves may be anchored inside the intestine. So even if the test is negative, your vet may ask you to bring additional stool samples on different days.

If parasites are the problem, there are a number of medications that will eliminate them, usually within 24 to 48 hours. You may be asked to repeat the treatment in three weeks and again in three months to make sure that the parasites don't come back.

When parasites don't appear to be the problem, your vet may take a look at the inside of your pet's intestines, using an instrument called an endoscope. This procedure can detect infections and other problems that may be causing the bleeding.

Anal sac infections are quite common, and, in most cases, easy to diagnose and treat. Most pets with infected anal sacs will need antibiotics to clear up the infection. Your vet will probably drain the sacs as well, which usually just takes a few seconds and can be done manually without special instruments or anesthetic.

In some cases, unfortunately, blood in the stool really is a sign of cancer. Your vet may use the endoscope to examine the pet's intestines for unusual lumps or growths. She may also check the outside of your pet to see if lumps have formed under the skin. If there are signs of cancer, your pet could need surgery, chemotherapy, or other treatments to bring it under control.

Other Causes of Blood in Stool 

A few common causes of digestive problems are exocrine pancreatic insufficiency, hair balls, intestinal obstructions, pancreatitis, parasites, and parvovirus. Learn more about these common conditions now.

Exocrine pancreatic insufficiency:
The pancreas is a small, complex organ that produces powerful chemicals that dogs and cats (and humans) need to survive. One part of the pancreas secretes insulin, the hormone that helps the body absorb the sugars found in foods. The rest of the pancreas secretes enzymes that are shipped to the intestines to aid in digestion.

When the pancreas doesn't produce enough of these digestive enzymes (a condition called exocrine pancreatic insufficiency), food will pass through the intestines without being broken down and absorbed. Pets with this condition will be hungry all the time. They will also lose weight and pass large amounts of soft, poorly formed stools. The stools may look greasy because of the large amounts of undigested fats they contain.

Without treatment, this is an extremely serious condition. Once it has been diagnosed, however, it is very easy to manage. Generally, all you will need to do is add a pancreatic replacement enzyme, such as Viokase or Prozyme, to your pet's food each time she eats, says Grant Nisson, D.V.M., a veterinarian in private practice in West River, Maryland.