Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that your pup Jameson had loose stools today in his kennel and tonight is passing clear (mucous) fluid.
Mucous in the stool indicates colonic irritation, and diarrhea also points toward colitis (inflammation of the large intestine).
In most cases mucous in the stools and loose stools are triggered by eating something they should not, too much table food, too many treats or something they find outdoors, a sudden change in diet, or gastrointestinal parasites. Stress can play a part, but s rarely the only factor.
More serious causes in puppies include viral or bacterial infections, a dietary allergy or sensitivity, congenital internal organ failure (kidney or liver disease), or a partial gastrointestinal obstruction.
In a young dog, especially one that hasn't finished his vaccine series, a viral infection, parasites or eating foreign material would be the most likely cause.
If this continues for more than a day, ideally he would see a veterinarian.
For now there are some things we can try at home, but if he isn't responding quickly he should see a veterinarian promptly.
If he has any vomiting or his appetite seems less to try and settle his stomach you can give either:
1) Pepcid ac (famotidine) at a dose of one 10mg tablet per 20 to 40 pounds of body weight every 12 hours
2) Prilosec (omeprazole) at a dose of one 20mg tablet per 40 to 80 pounds of body weight every 24 hours
These are acid reducers and may help him feel less nauseous and hopefully improve his appetite. They are quite safe and can be used for several days if necessary.
I would food fast him for 24 hours. This should help slow down spastic gut motions and soothe his irritated intestinal tract.
After his food fast offer a bland diet of 1/3 boiled, minced, white skinless chicken or boiled, lean hamburger and 2/3 boiled, white rice mixed with some low salt chicken or beef broth to make it easy to lap up and swallow and get additional fluids into him. Add 2 tablespoons of canned pumpkin (not pie filling, just pumpkin) to each meal as fiber soothes an irritated colon.
If things go well and he eats the bland diet and his loose stools firm up and the mucous is no longer present in his stools then feed him the bland diet for 3 to 4 days then slowly start to mix back in his regular puppy food, a little more at each meal. It should take about 5 to 7 days to slowly convert him back to her regular diet.
If he continues to have a decreased appetite even with the acid reducers, runs a fever (more than 103F rectally), or has a lower than normal temperature (less than 99F), has a tense painful belly, his diarrhea continues, or if he refuses to eat he should see a veterinarian for an examination, diagnostics, and supportive care.
Even if he seems to improve ideally you should have his veterinarian check at least a couple fresh stool samples too for parasites as parasite eggs/cysts commonly cause mucous in the stools, and are shed intermittently. They may be picked up on the second sample or third test even if the first is negative.
Please let me know if you have any further questions.