Whether or not your pet is showing gastrointestinal symptoms, their stool may contain various microorganisms that require treatment. The sample collected can help confirm or rule out the presence of parasites, for example. Certain tests may also be performed to identify specific bacteria (and even some viruses) when an animal presents with signs such as chronic diarrhea. With this information, your veterinarian can recommend the appropriate treatment for your companion.

To determine which tests should be performed on the stool sample, your veterinary team will ask several questions. Does your pet have diarrhea? Is it acute, chronic, or intermittent? Is your pet receiving intestinal parasite prevention? Has your pet had fleas recently? Is there blood or mucus in the stool? Is your cat strictly indoors, or do they go outside and catch mice? Has your pet gotten into the garbage or eaten a new food? Are other pets or family members ill? What is your pet’s diet—kibble, raw meat?

All of this information helps guide the selection of the most appropriate diagnostic tests.

For a stool sample to be valid and accurately reflect your pet’s condition, it must be fresh. A sample that is several days old, collected from the backyard or litter box, may not provide reliable results. If your pet has a bowel movement a few hours before your appointment, it is generally recommended—unless otherwise advised—to store the sample in the refrigerator until your visit.

If you find a worm in your pet’s stool, bring it to your veterinarian along with the fecal sample. Some worms, such as roundworms (ascarids), are easily visible to the naked eye. In the case of tapeworms, which resemble grains of rice, the eggs are contained within the segments. Do not be surprised if a fecal analysis is still recommended even if you bring in a specimen. Pets can be infected with more than one type of parasite, and accurate identification is essential to prescribe the appropriate treatment.

Various laboratory techniques are used to detect parasites and other microorganisms in pet stool samples. Depending on the veterinary facility, tests may be performed in-house or sent to an external reference laboratory. When conducted at the clinic, veterinary technicians typically perform the analyses and identify the parasites.

Below is a brief overview of the different tests that may be performed and their purposes.

Coprology is the analysis of fresh fecal matter used to detect the eggs of intestinal worms, as well as certain single-celled parasites (protozoa). In some cases, when an animal has a heavy parasite burden, worms resembling spaghetti or grains of rice may be visible in the stool. However, in most situations, adult worms remain within the digestive tract, and only their microscopic eggs are shed in the feces.

Although not always visible to the naked eye, these parasites can be present in large numbers and cause discomfort, poor growth, diarrhea, or blood in your pet’s stool. Depending on the type of parasite, an animal may show no clinical signs and be considered asymptomatic. This may lead some to question the importance of testing. However, an asymptomatic patient may eventually develop symptoms if the parasite burden continues to increase.

Additionally, tiny worm eggs can adhere to your pet’s fur and spread throughout the environment. Thousands of microscopic eggs or organisms may then contaminate your backyard, home, dog park, or favorite walking path—posing a risk to other animals. Some gastrointestinal parasites have zoonotic potential, meaning they can be transmitted to humans. Children and immunocompromised individuals are at higher risk of infection, and cases of parasite migration to the liver or eyes have unfortunately been reported.

Various laboratory techniques are used in coprology. Some parasite eggs can be readily identified under the microscope using a “flotation” technique. Flotation involves mixing a small amount of stool with a solution that has a higher density than most parasite eggs. As a result, fecal debris sinks to the bottom of the tube while the eggs float to the surface. The eggs can then be collected, identified, and counted under the microscope.

Other parasites, such as Tritrichomonas foetus and certain species of Giardia, are more difficult to detect using flotation and may require alternative methods (e.g., Polymerase Chain Reaction [PCR]) for accurate identification.

A fecal smear involves spreading a thin layer of stool onto a glass slide for microscopic examination. This technique helps assess your pet’s bacterial flora and can sometimes reveal certain types of parasites.

An overgrowth of a specific type of bacteria or the presence of numerous Clostridium organisms (which appear rod-shaped, often described as “baseball bat” shaped) may help explain an animal’s diarrhea and guide appropriate treatment.

In very fresh stool samples, it may also be possible to visualize Giardia organisms on a smear; however, PCR testing is generally more sensitive and reliable for detection.

In cases of chronic diarrhea, if your pet is fed a raw meat diet, or if an abnormality is detected on a fecal smear, a stool culture may be recommended. The fecal sample is mixed with a culture medium specifically designed to promote bacterial growth. After several days, the bacteria that have multiplied can be isolated and identified under the microscope. When bacteria are present in low numbers, a PCR test may also be performed.

It is completely normal to find bacteria in stool. However, depending on their quantity or type, some may be considered pathogenic and therefore responsible for diarrhea in the patient.

In conclusion, although collecting a stool sample may seem unpleasant, the tests performed on it can provide valuable information about your pet’s intestinal flora. A healthy gut flora supports your pet’s overall health, and ensuring the absence of intestinal parasites also helps protect both your pet and your household from these unwanted organisms.