Is Your New Pet’s Stomach Acting Up? Here’s Why (and What to Do)

When animals are grouped together, the chances of picking up contagious stuff — parasites, viruses, and bacterial infections — are higher. Gastrointestinal issues are common among rescue dogs and cats in these environments. The good news? Most of these digestive issues are super treatable — or they’ll just clear up once a pet settles down in their new home. Read on to learn why your new cat or dog might be having some tummy trouble after you bring them home.

Do many shelter pets have GI upset?

Dogs, cats, puppies, and kittens in shelters are vulnerable to a host of potential illnesses. Some animals arrive infected with parasites and viral diseases, and others pick up these illnesses after they arrive. Gastrointestinal illness is common in shelter pets as a result of intestinal parasites such as roundworms, hookworms, whipworms, coccidia, and giardia. Shelters and rescues work diligently to prevent and minimize these issues, but naturally, there will still be occurrences. Depending on the shelter’s medical resources, budget, and the timing of adoption, some adopters might find that their new pets develop gastrointestinal symptoms, such as vomiting and diarrhea, once they are home. But there are other causes of digestive upset.

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What causes GI upsets?

Many factors influence this risk, such as the number of animals at a shelter, the stressful nature of acclimating to a shelter environment, the age of the animals, the side effects (or absence) of preventative and ongoing medical care, and overall hygiene at the shelter. Meanwhile, younger animals are more susceptible to viral diseases and parasites because they have not received a full series of vaccines or intestinal parasite treatments. Here’s a look at some reasons your pup’s stomach might be feeling off.

Shelter stress is real (and it hits the gut)

The shelter system is overwhelming — loud, crowded, overstimulating, and scary for even the calmest dogs and cats. While there are exceptions, most animals find this stressful. One of the main ways this stress manifests is through GI upset. 

High stress elevates cortisol levels and slows gut motility, which leads to poor absorption of food and water, plus inflammation. Stress results in gut bacteria changes, diarrhea, vomiting, and loss of appetite. Shelters and rescues mitigate some of the effects of stress on animals by creating as quiet and clean an environment as possible, promoting good nutrition, and offering preventative, proactive medical care to fight parasites and viral infections. 

Even after animals are adopted, their stress may follow them into a welcoming, comfortable home. When given time to decompress in their new homes (follow the 3-3-3 rule), most rescued dogs and cats will ultimately settle in, and any stress gastroenteritis will tend to resolve itself. 

Sudden food swaps 

When pets enter a shelter, they are most likely fed a new brand and type of food that they are not accustomed to. This abrupt change, along with the stress of being in a new, scary environment, can lead to diarrhea and vomiting. 

Shelters and rescue organizations run on donations of money, pet food, and other supplies, so they aren’t always able to feed the same diet to their dogs and cats each day. Most dogs and cats do best with a consistent diet, eating the same food day to day. Switching pet food abruptly to another is a common cause of diarrhea — and not just those in rescue and shelter situations. 

Ideally, changes should be done gradually over a week or even more, mixing in small amounts of a new food with the old food, removing small portions of the old food. So, by the end of a week or two, they will have successfully transitioned over to the new food. Although some dogs and cats may have an “iron stomach,” most don’t adjust to abrupt changes, especially when they are stressed in a shelter. 

Parasites and infections

Unfortunately, it is very hard to find shelters that are parasite- and virus-free, even in well-funded and clean shelters. Most shelters and rescues check stool samples and treat empirically for intestinal parasites. Regular checks and treatments definitely decrease the incidence, but don’t guarantee that adopted pets will be parasite-free when they go to their forever homes. This is because effective treatments need to be done over weeks, and at shelters, reinfection is very possible. 

The same goes for viruses and vaccines. Most pets aren’t in the shelter long enough to receive the entire vaccine series needed for full immunity. So, as they come and go, dogs and cats can carry and spread viral diseases that can cause GI symptoms. 

These parasites are endemic in most environments where dogs and cats live. Common parasites found and treated in shelter animals include:

• Roundworms

• Hookworms

• Whipworms

• Coccidia

Parasites can come into the shelter in many ways.

• Intestinal parasites are passed from mother dogs and cats to their puppies and kittens.

• Puppies and kittens are also exposed to parasites from ingesting fecal material in their kennels and yards. 

• Asymptomatic dogs and cats who enter the shelter may be carrying internal parasites. 

• Viral infections are also very common in unvaccinated stray dogs or neglected dogs who may enter the shelter.

It is very important for adopters to have their pets examined by a veterinarian as soon as possible to be sure they receive treatments for intestinal parasites and viral diseases. 

Although it is upsetting to some, adopting a dog or cat and finding out they have coccidia or giardia at their first vet visit is pretty common. Treatments with medication are generally effective when adopters follow the directions and clean up carefully after their pets. 

Unlikely but possible causes of GI symptoms in shelter pets

Although most shelter dog GI issues involve parasites, viruses, food changes, and stress, there are other possible causes not related to the shelter. If diarrhea, vomiting, and loss of appetite don’t fit the clinical picture of parasites or a viral disease, these other issues should be considered:

• Foreign objects stuck in the GI tract (such as toys, string, or bones)

• Cancer and systemic illnesses such as liver failure and kidney failure, pancreatitis, and Addison’s Disease

• Toxicity

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How to help your rescue pet’s gut

There are many things pet parents can do to minimize GI issues in their new dogs and cats. 

Switch to new food slowly

Find out what the shelter or rescue has been feeding them, so you can continue the same brand and flavor when you bring your new pet home. If that’s not possible, start with a bland flavor such as lamb and rice, which tends to be a little easier on the GI tract. 

Once they’re home and settling in, if you choose to change their food, transition slowly over one to two weeks by adding the new food to the daily ration while decreasing the amount of the old food. Using a probiotic for dogs or a cat-specific probiotic can help keep gut flora healthy. 

Get their stool checked

Checking a stool sample at the first vet visit is highly recommended. If parasites are detected, your veterinarian will prescribe medications to treat them. They might also make dietary recommendations. 

If diarrhea and other GI symptoms persist, more involved diagnostics may be needed. Sometimes, especially with giardia and coccidia, multiple rounds of medication are necessary to fully treat parasites. Meanwhile, annual pet exams can help keep your pet parasite-free.

Keep diets bland

If pets develop diarrhea, change to a bland diet of white rice, boiled chicken, or low-fat cottage cheese for a few days before gradually going back to the regular diet. Check with your veterinarian for further recommendations. 

Be patient, some GI issues in shelter pets, as with any pet, can be complicated and need to be sorted out over time.

Never use human medications

Never use over-the-counter human medications to treat your dogs and cats without checking with your veterinarian. Many human medications are highly toxic to pets.

When to call a vet

Dogs and cats, like people, can have simple stomach and intestinal upset that lasts for a few hours. These animals will usually maintain typical energy levels and might even want to eat. 

For cases of simple diarrhea, treating symptomatically by switching to a bland diet and adding a probiotic might be enough. But when animals are vomiting continuously, have blood in their stool, are lethargic, are not eating, have abdominal bloating, or are in pain, it is definitely time to see a veterinarian. 

At any point, a call to the vet is advisable to check in, let them know the symptoms, and get their advice for moving forward. It’s always best to err on the side of caution and have pets checked. Sometimes there are underlying issues, or something more serious going on that you aren’t able to detect at home. 

Commonly asked questions

Is it normal for a new dog to have diarrhea?

Yes, unfortunately it is very common for a new dog or puppy to have diarrhea. Causes of diarrhea in new dogs include intestinal parasites, viruses, changes in diet, and stress from moving to new, unfamiliar environments. In older dogs, diarrhea might be caused by inflammatory bowel disease, cancer, and other systemic diseases that affect the GI tract. Many of these issues are mild and easily treated, while others can be very serious and costly to treat. 

How long does GI upset last in dogs?

Depending on the cause, GI upset can last for a day or two, a week or two, or become chronic, lasting for an extended period. Your dog may respond to a bland diet, probiotics, and possibly antibiotics in a matter of hours to days. When parasites are treated with specific medication in addition to a bland, soothing diet, GI symptoms usually resolve relatively quickly. However, parvovirus and other viral diseases can be very serious, with the illness lasting for one to two weeks or longer. Intensive hospital care is necessary for successful treatment and recovery from these viruses. More chronic illnesses secondary to inflammatory bowel disease and cancer can last for long periods. 

What does GI upset look like in dogs?

Generally, signs of gastrointestinal issues include vomiting, diarrhea, loss of appetite, and weight loss. Depending on the cause, dogs might feel and act fine while having diarrhea and/or vomiting. Or they can become weak, lethargic, and very ill. If this is the case, a veterinary visit is crucial to diagnose and treat a potentially serious illness. Parvovirus in young puppies is very serious. Thankfully, there are new treatment options available that are very effective when diagnosed early.  

Is it normal for a newly adopted cat to have diarrhea?

Unfortunately, parasites and viruses may infect kittens and cats coming from shelters — as well as catteries — which can cause diarrhea in cats. Many times, these cats seem fine at the shelter. But when moved to their new home, the stress of the change in environment triggers parasites and viruses that have been latent (or at least not causing issues) prior to the move. Changes in food and treats can also wreak havoc on the GI tract of pets being adopted and moving into their new home environment. 

What are the symptoms of GI issues in cats?

Cats can develop diarrhea, vomiting, loss of appetite, and weight loss. These symptoms may be accompanied by lethargy, or a cat may have full energy, depending on the cause. 

What is an inflamed GI in cats?

Inflammation of the stomach and intestinal wall is usually caused by changes in motility and gut flora (bacterial population), with the gut responding to changes in diet, increased stress, parasites, and viruses. The inflammation usually resolves with short-term treatment. Cats can get many primary inflammatory diseases of their intestines, known as inflammatory bowel disease. These changes become chronic and can cause diarrhea, vomiting, and weight loss. Treatment includes removing potential triggers, such as specific foods, and medicating with steroids and other immunosuppressive medications. 

How long does it take for a cat's stomach to get used to new food?

It’s usually best to transition cats slowly to a new food. One to two weeks is usually enough time to avoid reactions to the new food. If a particular food isn’t working for your cat, discontinue that food and go back to a previous food that was working. Check with your vet for recommendations for a food that matches your cat’s overall health and medical needs. 

References

‌Cohen, Aly. “Parvovirus: Transmission to Treatment | Cornell University College of Veterinary Medicine.” www.vet.cornell.edu, Apr. 2024, www.vet.cornell.edu/departments-centers-and-institutes/riney-canine-health-center/canine-health-information/parvovirus-transmission-treatment.

“Diarrhea | Cornell University College of Veterinary Medicine.” Www.vet.cornell.edu, www.vet.cornell.edu/departments-centers-and-institutes/riney-canine-health-center/canine-health-information/diarrhea.

“Disorders of the Stomach and Intestines in Dogs - Dog Owners.” Merck Veterinary Manual, www.merckvetmanual.com/dog-owners/digestive-disorders-of-dogs/disorders-of-the-stomach-and-intestines-in-dogs.

Rose, L., et al. “Efficacy of a Probiotic-Prebiotic Supplement on Incidence of Diarrhea in a Dog Shelter: A Randomized, Double-Blind, Placebo-Controlled Trial.” Journal of Veterinary Internal Medicine, vol. 31, no. 2, 10 Feb. 2017, pp. 377–382, https://doi.org/10.1111/jvim.14666.