Diarrhea and loose stool are probably one of the most common complaints of dog owners. While there are a ton of reasons why your dog may be having issues, this is meant to be informative and should never replace the advice of your veterinarian. Diarrhea can be a very simple issue, but it can also be indicative of potentially serious conditions and if your dog is having some real issues, they need to go to the vet.
Acute diarrhea, or diarrhea that seems to come fast and out of nowhere, is one of the most common types of things seen at a clinic. Often times, it is because we have changed our dogs food either too often or too quickly; our dogs digestive systems are not as tough as ours. If we do not slowly change their food (little by little, over no less than a week), or we change it too often, our dogs may have persistent loose stool or diarrhea. Often owners change their food, and notice symptoms. They panic, and then change it again. They panic once more, and change it again. Thusly the horrific cycle of diarrhea; we need to change their food slowly, and then keep them on it. Switching diet or introducing a ton of new snacks all the time does our dogs' digestive system no justice.
Is your dog on any prescription meds? Is he under stress? Sometimes dogs will get the runs merely because they just took a long car ride that they didn't appreciate. I think more often than not, regarding an adult dog, this tends to be the case. Diet change and stress can do a lot. At adoption events, many of the dogs had the runs during their potty breaks. I always feared a potential adopter would see and think they were sick. Their foster knew their stools were fine at home, but the stress of the car ride and being at the event took it's toll. One of my dogs got the "scoots" because I gave him a new dog snack over a couple of days, which had questionable ingredients. Meaning, they were the "good" snacks that smell great but are really made of junk. His body told me so. His scoots lasted a couple of days and then were done. Christie's dog, Reese, gets the scoots from Colitis flare-ups. Colitis literally just means "inflamed colon", and the general theory regarding Reese is that they were brought on by stress.
There are viral, bacterial, and parasitic reasons for diarrhea, and your veterinarian needs to examine your dog's fecal and give you a diagnosis. Virally, we are most familiar with Parvo, which tends to impact puppies, though it can hit dogs of all ages. Puppies' immune systems are not as great as adult dogs, and it makes them more vulnerable. I heard a case of a 13 year old dog who was diagnosed with Parvo. Distemper, Coronavirus, and feline panleukopenia (kitty parvo) all cause diarrhea. There are many bacterias which cause diarrhea also, as well as protozoas like Giardia. It would take too long to go into all of these separately, but expect more blogs!
On the whole, an adult, healthy dog is likely to have diarrhea due to change of diet or stress. What is recommended is to fast your dog for 2 days. It sounds horrible, but too often we want to feel inclined to keep feeding them in hopes more food will equal solid stool. In reality, their digestive tract needs to be allowed to calm down. Something upset it. If we allow a fast, then we can introduce boiled chicken and rice; something bland which won't upset their GI tract. We will notice a return to "normal" function and then can resume their normal routine. Never do *anything* with your dog until you have spoken with or seen a veterinarian. This fasting/bland suggestion is very general, and each dog has specific needs and underlying health conditions.
Always give your vet a call. Often times you can discuss the symptoms and history of your dog, and they will guide you in the right direction. The behavior of your dog regardless of the diarrhea will likely help your vet make the determination. If everything is fine other than the scoots, they probably have an upset tummy. Changes in behavior, ie. lethargy, vomiting, etc. should all be taken very seriously and your buddy should make a trip to the vet right away.