Probiotics for diarrhea?

Many people use pumpkin for this, and oddly enough, it seems to work for constipation too.  If it's related to antibiotics, you might try using some yogurt for a few days.  Buy the whole yogurt with active bacteria.  You can buy probiotics at the health food store and it comes in a variety of forms.  I'd ask someone at the store to help you pick the best one.

Thanks for the suggestion.
 
Yogurt isn't an option because he won't eat it, and dairy doesn't usually agree with him anyway.
 
Has anyone had any experience with Acidophilus+ or OptaGest? I think I've narrowed it down to one of those, but I can't decide which one to try.

If he's not very good with dairy- go with a non-dairy probiotic. You'll have to seek it out as many of them are dairy based. Country Life makes a good non-dairy one and many other brands make them also, but the CFU's vary . Look for billions of colony forming units per capsule (a small yogurt has 1 billion but caps can go up to 10 billion). There are also soil based organisms, another probiotic type.

Do you know what's causing the diarreah? Has it been happening for long?

It's been happening for about 2 weeks. So far, tests have come up negative and it's being chalked up as something that just happens to an older dog. He hasn't lost any weight and his appetite is unchanged.
 
I put him on a one day fast, and that did improve his stool, but no matter what he eats now, it seems to cause diarrhea to varying degrees. (Everything from very soft to mildly runny to completely liquidy.)

Have you tried blueberry or vanilla yogurt? Murf LOVES those flavors......

Do you know what type of tests the vet did?
Bacteria, Giardia, Coccidia, Whipworms, all kinds of things can cause diarrhea.
To have suddenly developed this sounds odd, I have no idea why the vet would say that about 'older dogs'. There must be a reason. Thankfully he feels well, still has a good appetite.

If all of that has been ruled out perhaps food is making him sick.
Has his diet changed at all? Any new treats?
Some dogs will get diarreah from food allergies. Even a one doggie biscuit with a lot of grain can set off a spell of diarreah.

Also in the warm months bacteria grows quickly on chew treats (rawhide, pig ears, etc.) that are left around the house and things in the yard. Animal dropping in the yard can carry parasites and bacteria, does he eat things in the yard?

Does he eat kibble? Is it stored in a cool dry place? You may also want to check the expiration date on the bag too. The fats can go rancid, there may be something wrong with the kibble even.

If all of his tests come up fine perhaps it's something simple. You mentioned he responds to a food fast, yet when he eats again he gets diarrheah. I may look into the food if I were you.
Unless it's some type of pancreatic deficiency he''s getting, where he doesn't have proper enzymes to break down food (the fats and everything tend to pass through all too easily).You said he's keeping his weight up though, so it may not be a problem such as that.

If you put him on a plain basic food after he comes off of his fast (perhaps chicken and boiled potato), are the stools any better?