Diarrhea lasting for several days in an older dog is always worrying. While a single episode of loose stool may be minor, a week of ongoing diarrhea signals that something deeper may be affecting your dog’s digestive system or overall health.
We outline the common causes of diarrhea lasting a week in old dogs, what you can do at home, and when to seek veterinary help.
Old Dog Diarrhea for a Week — Why It Happens
When diarrhea in an old dog continues for a week, the most common reasons include dietary issues, intestinal parasites, infections, inflammatory bowel disease, organ dysfunction, and even cancer.
Senior dogs are more vulnerable because their immune systems are weaker, their digestion less resilient, and their bodies less able to recover from fluid loss. Prolonged diarrhea in an older pet is never normal and requires attention.
Old Dog Diarrhea for a Week: Common Causes
Dietary Indiscretion or Food Sensitivity
Even in their golden years, many dogs will still get into things they shouldn’t. Eating spoiled food, garbage, or fatty table scraps can upset the digestive system and lead to prolonged diarrhea.
Old dogs may also suddenly develop sensitivities to ingredients they previously tolerated, such as chicken, beef, or grains.
If the exposure continues daily—such as with their food—diarrhea may persist for a week or longer. Other signs often include gas, bloating, or occasional vomiting.
Read more: Old Dog Poop Like Jelly With Blood (Why it happens and what to do)
Intestinal Parasites
Parasites aren’t just a puppy problem. Senior dogs can contract roundworms, hookworms, whipworms, or giardia, all of which can trigger diarrhea that doesn’t resolve quickly.
With weakened immunity, old dogs may have more trouble clearing these infestations. Persistent diarrhea caused by parasites is often accompanied by weight loss, poor coat condition, or blood and mucus in the stool. Left untreated, it can lead to dangerous dehydration.
Bacterial or Viral Infections
Pathogens like Salmonella, E. coli, or Campylobacter can cause severe diarrhea lasting days to weeks. Viral illnesses such as parvovirus are less common in vaccinated senior dogs but can still affect older, unprotected pets.
Infections irritate the intestinal lining, causing frequent watery stools that persist until the infection resolves or is treated.
Fever, loss of appetite, and lethargy may also appear. In old dogs, these illnesses can take a heavier toll and become life-threatening more quickly.
Inflammatory Bowel Disease (IBD)
Chronic diarrhea that stretches over a week may signal a condition like inflammatory bowel disease. IBD occurs when the immune system mistakenly attacks the gut lining, leading to ongoing inflammation.
Old dogs with IBD may experience alternating diarrhea and constipation, vomiting, and weight loss.
The condition requires veterinary diagnosis and long-term management with medication and dietary adjustments. It’s not something that will resolve on its own.
Liver or Kidney Disease
When vital organs like the liver or kidneys begin to fail, toxins build up in the bloodstream, affecting digestion. Chronic diarrhea is a common side effect.
In an old dog, diarrhea lasting for a week may be a red flag that organ function is compromised.
Other symptoms often include increased thirst, frequent urination, vomiting, yellowing of the eyes or gums, or a dull coat. These systemic diseases must be diagnosed with bloodwork and require veterinary care.
Cancer of the Digestive Tract
Sadly, one of the more serious causes of prolonged diarrhea in senior dogs is cancer affecting the stomach, intestines, or surrounding organs.
Tumors can disrupt digestion, block nutrient absorption, and cause bleeding within the gastrointestinal tract.
This type of diarrhea usually does not resolve without treatment and is often accompanied by weight loss, loss of appetite, or blood in the stool.
Because cancer is more common in older dogs, it must always be considered when diarrhea lasts beyond a few days.
What to Do If Your Old Dog Has Diarrhea for a Week
If your old dog has had diarrhea for seven days, supportive care at home can help while you arrange a veterinary appointment.
First, ensure your dog stays hydrated. Older pets lose fluids quickly, so provide plenty of fresh water and encourage drinking. Offering ice cubes or low-sodium broth can help if your dog is reluctant.
Second, feed a bland, easily digestible diet. Options like boiled chicken with plain white rice, or a prescription gastrointestinal diet, can give the gut a rest. Feed small, frequent meals rather than large portions.
Third, monitor for improvement or worsening signs. If the diarrhea stays the same or worsens after switching to bland food, this indicates that the cause is more serious than simple dietary upset.
Lastly, avoid giving over-the-counter medications unless directed by your veterinarian. Some human medicines, including anti-diarrheal drugs, can be dangerous for dogs, especially seniors with organ issues.
When to Call or Visit Your Vet
One week of diarrhea in an old dog should always prompt a veterinary consultation. Unlike younger dogs, seniors don’t recover as quickly and are at higher risk of dehydration and complications.
Call or visit your vet right away if you notice any of the following:
Blood, jelly-like mucus, or black tarry stool
Vomiting along with diarrhea
Refusal to eat or drink for more than 24 hours
Lethargy, weakness, or collapse
Weight loss over a short period
Signs of pain, bloating, or straining
Your vet will likely run stool tests, bloodwork, and possibly imaging to pinpoint the cause. Prompt diagnosis not only relieves discomfort but can catch serious conditions early.
Related: Old Dog Diarrhea (Causes and when to worry)
Key Takeaway
Diarrhea lasting for a week in an old dog is never normal and should not be ignored. While mild digestive upset can cause temporary loose stools, persistent diarrhea points to parasites, infections, inflammatory disease, organ dysfunction, or even cancer.
At home, you can support your dog with hydration and bland meals, but veterinary care is essential to uncover the underlying cause.
With timely attention, many senior dogs recover well, and early treatment can make a huge difference in their comfort and long-term health.