Our dog, a poodle, started the same pattern you are dealing with starting at abut 6 months old. Our initial vet tried many things, trying special foods, medications, and there would always be improvement, but then break throughs of symptoms again. Then in a particularly bad episode I had to take her to Friendship, not our regular vet, late one evening. They gave her fluids but also ran a series of expensive blood tests. It turned out she had pancreatitis, which they suspected was a low-grade, chronic form, probably congenital. Initially treated with Carafate and a probiotic paste, but the long term treatment is a low fat diet. She has been on Honest Kitchen Preference that we mix with ground turkey breast -- the lowest fat protein she can tolerate. She has been completely symptom free for 18 months and really thriving. We make the turkey, then freeze it in packets that are the right portion size to be mixed with the Honest Kitchen each day. It is pretty easy and has been a lifesaver for our dog. Strongly recommend a second opinion, not necessarily Friendship though as our dog was traumatized by her emergency experience there. Am sure other dogs react might react differently, but it took a lot of desensitizing with a home vet and home groomer before she was OK with being handled by anyone but us. Before that night, she had loved her vet and groomer and neither could believe the change that had occurred after that visit.

I went through this with my youngest dog, who, it turns out, has IBD (Inflammatory Bowel Disease). After many treatments for parasites and bacterial infections that didn't solve the problems, many changes of diet, and no end to the periodic bouts of diarrhea, we finally had him evaluated by Dr. McConnell, the consulting internist at Friendship: http://www.friendshiphospital.com/about/consultants.html#mcconnell . Our pup had a colonoscopy to confirm what was going on in his gut – a procedure requiring sedation, but, as it turns out, well worth it for a clear diagnosis and a way forward. Under the vet's supervision, our pup for several months had a diet of *exclusively* sweet potato and low-fat cottage cheese. I am not kidding. Bright orange poops, but a complete end to the diarrhea and upset tummy. After a followup with Dr. McConnell, he has now transitioned to a dry venison-based diet and is doing fine. He also gets periodic Vitamin B12 shots. The change in his health and in our lifestyle is incredible. I was skeptical of the whole workup and weird diet routine, but compared to dealing with diarrhea and constantly trying to guess was wrong this time, it has been SO worth it. I would STRONGLY recommend seeing if you can get a consult with Dr. McConnell.

Your poor dog clearly has stomach issues.
You should probably change her food. You may have to experiment till you find something suitable. If you are local the pet stores like Bark or Whole Pet Central have sampler sizes of most of the foods.
The Honest Kitchen makes a variety of high quality foods, with different protein sources.
People have used slippery elm powder with success in dogs for IBD. A holistic vet may be worth consulting. The Tylan mentioned by a PP can also help.
However in the absence of parasites or any obvious disease, the simplest thing would be to change her food and see how she responds.

British purebreds need a British diet: Fish and potatoes, beef and green peas, chicken and carrots. They're INCREDIBLY picky and can only tolerate the blandest of food. Just like British people…

My dog sounds similar. After dozens of foods, taste of the wild salmon formula is the first one she can handle. It's a lower protein food, which seems to help. Bonus that it's relatively affordable.

I have terriers and there is no way I can feed the Blue Buffalo. It is too rich--causes diarrhea in many breeds. A pure bred dog from the british isles needs fish, chicken,fish oh, and chicken and fish. Buy a can of salmon and mix it with bits of potato-for some pure breeds that are so specifically engineered recently that they've adapted to whatever the local people in the villages where the dogs were bred eat. So, boil a chicken until the bones are soft and mushy and give the dog that too. Sorry, but when you get a pure bred you get their idiosyncrasies, too.

We had a similar issue with our dog, including the fact that she had worms when she got rescued and had extensive treatment that made her sick. I definitely second others who have suggested that you seek another opinion. My first vet was treating the symptoms and not addressing any underlying causes. They kept prescribing Lomotil (dog immodium) and metronidazole (these huge horse pills that she would spit out). Her file was like 2 inches thick and nobody was putting together a pattern.

My second vet was much better, and very simple and straightforward. He began treating her with Tylan powder (also called Tylocin). If you haven't already tried it, it may help. It's a powder you can sprinkle in their food so they can't avoid it like they can with a pill. He also suggested (don't laugh) that we give her the Metamucil crackers made for humans. It sounds ridiculous but he suspected that part of her recurring problem was an insufficient amount of fiber causing an imbalance in water absorption in her colon. It seemed totally counterintuitive to us because we always associated fiber with pooping MORE but we learned that fiber is a regulator more than anything else, and believe it or not, it worked.

For our dog, it also seemed like stress would trigger the flare-ups. We noticed a pattern after we'd take her to Petco to get her nails clipped (stopped doing that) or if there was a particularly bad storm. She had a pretty traumatic first few years of life so it makes sense that as she's gotten older, it's subsided some. Not sure if stress would be a factor for your situation. Also, is there blood in the diarrhea? Our vet said that if there's blood, you can tell where the irritation is in the intestinal tract based on the color.

As for possible allergies, you mentioned you did a lot of tests, but have you tried anelimination diet?

I know how frustrated you must be at this point and I remember exactly that feeling, of getting angry with your dog and feeling guilty about it. I hope you get some answers.

We are on a grain-free hypoallergenic food for dogs with sensitive stomachs. I would absolutely not buy it if we didn't have similar issues with our dog. It's Pinnacle Breeder's Choice Trout and Sweet Potato, Dry. We have generally avoided the emergency vet for years having been on this.

I think these kind of problems (allergy issues) are common with Westies, so you may have to do like PP said and move on to another even more exotic protein after being on one for a while.

What about looking into a BARF diet? We are mostly raw with our dog, supplementing with Orijen kibble when we don't have enough for a meal. We also give her probiotic treats, plain yogurt, and veggie glop (leftover fresh vegetables blended with some water and apple cider vinegar). This regime can be time consuming, there are companies that sell freeze dried or pre-made raw meals. Financially (if you make meals yourself) it's comparable to premium pet food prices. Good luck to you and your dog.

Going Paleo seems to help humans with similar issues...

Listen to Ira Glass about his dog--they feed it all kinds of exotic meats until the dog develops an allergy and they have to move on to the something else:
http://m.thisamericanlife.org/radio-archives/episode/480/animal-sacrifice

I know a dog with bowel issues and he had them as a puppy. By about 6 months after much food/meds experimentation the dog has successfully eaten canidae grain free dry kibble for years. For a treat he eats Old Mother Hubbard veggie biscuits. He also gets a dab of reduced fat peanut butter inside a hollow white bone.

This dog is far larger than a westie -110 pounds - and leads a very active lifestyle. Repercussions of a 110 pounder with explosive poop are mind boggling.

Also since the OP and her significant other are not home all day there is the potential that others give the dog stuff or it is dropped on the floor. Also if feeding wet food use a clean dish for every meal.

Did you try switching foods? Our dog didn't do well on Blue Buffalo and our vet said it's one that he commonly hears dogs have problems with. Without getting into the debate over foods, not all "premium" foods work well for all dogs. Your dog may have a food allergy, which I would suppose is difficult to figure out. Our dog had some crazy digestive issues for a while, which seemed intractable, and I feared it would end up being a food allergy. Our vet tried a bunch of things all at once, which worked, but am not sure what his problem was. I do know that he can only have a small amount of foods that contain wheat. So a treat from the mailman, fine. A bun he grabbed from my toddler, tinkle poops for a whole day.

Firstly, seek a second opinion. She clearly has stomach issues. Second, note down how much you fed, what time and when did the loose motions happen. This will help the vets in figuring out more.

My dog had something similar and we found that probiotics helped a lot

We are at our wit's end with our westie. I think I've written about her before here, maybe. She's a 4 year old rescue dog. When we got her, she had worms, which required several rounds of treatment. She was not housebroken when she came it us (at a year old) and was difficult to house train.

She seems to have some sort of recurring stomach/intestinal issue. The pattern is she won't poop on a walk or two, then will have explosive diarrhea for several cycles, then be ok for a bit, then another prior of diarrhea, and so on. We once went 5 months without incident (last summer into fall), but she's been on a particularly bad cycle lately.

And I hate her for it. With two small kids, two working parents, two cats, an older home, a busy overflowing schedule - I just can't take this anymore.

We've had extensive testing done - the doctor suspected Addison's, based on the cycling between fine and flare up, but after well over $1000 in testing for every possible thing and multiple stool samples, we can't find anything specific wrong. We've switched to Blue Buffalo food and ONLY fed her that - no treats, no people food, no anything. There is nothing that seems to trigger a flare up. (we were switching flavors of the canned food after finishing a can, but we noticed that seemed to irritate the situation so we stick to the same damn flavor of wet food every time). She has a probiotic every morning, too.

After a particularly bad week last week (try getting woken up at 3 am by a terrible stench of dog diarrhea next to your bed!), we've banished her to kitchen at night, but honestly I'm not thrilled about cleaning up dog diarrhea every morning nor sanitizing our kitchen floor every day, nor thinking about all the disgusting things she is doing to our kitchen floor.

What can we do? What have we left unexplored? Do we move to making her damn food (rice/chicken?)? Is there some sort of guideline or protocol we can follow, outlined on some website someplace? Do we go to another vet, for a second opinion? Do we build a doghouse and keep her outside in a dog run, hosing it out? I am a dog lover - but I am just at the end of my rope. Any detailed advice appreciated.