Why Does My Dog Have the Runs After a Run?
There are few things Ted loves more than going out for a nice long run on the trails with his four-legged crew. Everyone comes home tuckered out but feeling great. Great, that is, until one of the dogs produces a pile of poop that looks like it came out of a garden hose.
And, yes, this happened to us recently, and it's the reason for this post.
Ted took the boys out for some lengthy runs last weekend during one of the last beautiful weekends of the season. Gus, in particular, may have logged his longest yet — somewhere around eight miles on Saturday, followed by another long one on Sunday.
After both sessions, he came home, drank a lot of water, and then, later in the afternoon, proceeded to have some spectacularly messy poops.
Naturally, my first thought was: Gah! It’s his fooooooooood! Do I have to change his diet?!? Because that's how the internet has prepared me to react to bad poop.
Bad poop = bad food.
And there was reason to initially suspect his diet. The company we order from was out of duck, so I ordered the duck and trout formula instead. They'd both had it before … did we have any issues then? I couldn't remember.
My second thought was: Wait a minute. When, exactly, did this happen?
And that second question is actually pretty important because as I was putting the patterns together in my head, I could see dots connecting.
So I headed to the computer to do some sleuthing.
Turns out that dogs can, in fact, get loose stools or diarrhea after strenuous exercise. That doesn’t automatically mean something is wrong, but the timing — and what happens afterward — can tell you quite a bit.
So ... why does running make my dog poop like that?
The short answer is that exercise can affect the gastrointestinal system.
Human endurance athletes know this well. Runners have an entire category of exercise-related gut complaints, ranging from cramping to urgent bathroom trips after long runs.
Boston Marathon runner Davis Clarke went viral in 2024 after he finished the race in under 3 hours and publicly admitted that he soiled his shorts towards the end of the course.
It happens, and dogs are not immune.
When a dog exercises hard, his body has a lot to deal with at once. Heart rate and circulation increase, muscles demand more oxygen and energy, and body temperature rises. Strenuous exercise can also affect gastrointestinal function, although researchers are still working to understand exactly how and why this happens in dogs.
Add in the physical jostling of running, excitement, stress, changes in routine, and possibly eating or drinking around the activity, and you’ve got a pretty good recipe for a digestive system that says: Yeah, you're going to be dealing with this later.
The harder and longer the exercise, the more likely some dogs are to have gastrointestinal upset. A dog who is accustomed to a couple of miles may also react differently when suddenly asked to run considerably farther. That doesn’t necessarily mean the exercise was harmful. It may just mean his digestive system wasn’t thrilled with the workload.
And then there's the water
This was another piece of the puzzle that made me stop the diet panic. After his extra long run, he came home and drank a bunch of water.
Which seems like exactly what you’d want a dog to do, right?
Well ... yes. But also, maybe not all at once.
Dogs need to replace fluids lost during exercise, particularly in warm conditions. But gulping large amounts of water right after strenuous exercise may contribute to stomach upset in some dogs, especially if the gut is already a little irritated from the activity.
So if your dog comes home from a long run or hike and immediately tries to drink the entire contents of the water bowl, it may be worth offering water in smaller amounts, more often, rather than allowing one enormous chug-fest.
We do have a no-mess water bowl, which does help limit the intake and we actively monitor both dogs while drinking — making them stop and take a break after a few gulps — to help manage how quickly they're drinking, but he still consumed a decent amount of water.
Don't forget what happened along the way
Strenuous exercise shouldn't be the only suspect.
Dogs on trails are notorious for sampling the scenery, isn't that right, Pike?
Puddles, ponds, streams, mystery “snacks” found along the path, and even a small woodland creature consumed during the outing can all cause loose stool, and none of them has anything to do with how far your dog ran.
So before you blame the mileage, think about what else could have contributed to the situation.
The most important question: when does it actually happen?
One episode of messy poop doesn’t necessarily tell you very much, but a pattern can.
If your dog has loose stool after a particularly long run but is otherwise acting completely normal, and his poop is back to normal within a day or two, that’s a very different situation from a dog who regularly has diarrhea after every exercise session.
Paying attention to the timeline is important. Ask yourself:
How strenuous was the activity, and was it much longer or harder than your dog’s usual exercise?
How soon after exercise did the diarrhea happen?
Did he eat or drink anything along the way?
Did he otherwise seem normal, with normal energy and appetite?
How long did the loose stool last, and did it return to normal once he recovered?
Does this happen every time he exercises, or only after unusually strenuous activity?
You don’t need to become a canine poop scientist. Although, let’s be honest ... if you own a dog, you’ve probably already earned the title.
The point is to look for patterns rather than panicking over a single episode. The pattern doesn’t prove exercise is the cause, but it certainly gives you something useful to discuss with your veterinarian if the problem persists.
When it's time to call the vet
Of course, “my dog has diarrhea after running” is not a diagnosis. There are plenty of reasons a dog can develop diarrhea, and some of them have nothing whatsoever to do with exercise.
Contact your veterinarian if the diarrhea doesn’t resolve, keeps happening, or comes with any of the following:
vomiting
significant lethargy or weakness
abdominal pain
refusal to eat or drink
blood in the stool
signs of dehydration
difficulty recovering after exercise
excessive panting or other signs of overheating
And if your dog has a swollen, tight-looking belly or is retching without producing anything, don’t wait. That can be a sign of bloat, and it’s an emergency. The same goes for a dog who appears seriously ill after strenuous exercise, particularly in hot or humid weather. That’s not a “let’s see what his poop looks like tomorrow” situation.
That’s a call-the-vet-right-now situation.
So ... what was the verdict with Gus?
Honestly? I don’t know for sure. And that’s OK.
The boys had an unusually big weekend of exercise. They both drank a lot of water afterward. Gus had some impressively messy poops. And then his digestive system moved on with its life and everything is back to normal now.
It certainly seems like the extra-long runs were the issue.
That dog is a complete and total mystery to me. He once ate my SpotBot carpet cleaner and never had any issues, but let him run loose on the trails for an hour or two and, well, there aren’t enough bags in the world to clean up what he leaves behind.
It’s a good reminder that dogs’ bodies don’t always respond to increased activity exactly the way we’d expect.
If it happens after his next long run, we’ve got a pattern. Ted will just have to make sure his runs are shorter than Pike's. And if the pattern comes with other symptoms or doesn’t resolve normally, that’s when we’ll stop laughing about poop and start talking to his doctor.
Because sometimes the answer to “What’s going on?!?” really is: Probably nothing.
And sometimes it’s: Hmm. Let’s keep an eye on that.
And occasionally, it’s: Call the vet.
The trick is figuring out which one you’re looking at. And, as always, your dog’s poop is probably going to be one of the clues.
As always, this post is for informational purposes and is not a substitute for veterinary care. If you have concerns about your dog’s health, contact your veterinarian.
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