Hmm, let's see, I studied for endless hours skipping & searching all over the place so it's hard to recall what I read & where.
The main points that sunk in to my addled brain is that the dog PB's are "stabilised" which gives them the chance to get right deep into the gut before reacting rather than being destroyed by low pH or other acids before they got into the true digestive part of the stomach. Also, another important factor is that every single dog's gut flora is different based on their diet, among other things.
I also recall reading about some dog PB's advertise so many different wondrous strains in terms of billions & trillions of "live bacteria" and it's all a crock, merely an advertising farce. There is one particular PB in dogs, Enterococcus faecium, that's not in human PB's to my knowledge, and it's mentioned in the first link provided below.
As an aside: The other thing I remember is that with enzymes, mix them into the food and let it stand for about 10 minutes to give them a chance to start developing is most beneficial. Also, apparently enzymes die as we get older and are not replaced so, to my mind, they are super beneficial to the digestion of young pups and older dogs. I actually make my own enzyme fruit juice drink that I'm about to start drinking - hopefully it'll clear the fog in the head and these unco fingers that don't type what the brain is dictating lol
Probiotics For Dogs - Canine probiotics - Pet Probiotics
Interesting info on strains & technical mumbo jumbo from one of the brands I was hoping to get:
Probiotics for Pets: Understanding Strains and CFUs
A great article on herbal PRE-biotics, to help PB's along, in the form of inulin:
Probiotics for Dogs - Whole Dog Journal Article
Canadian Vet Uni article showing how some PB strains "adhere" in humans but probably not dogs:
Preliminary evaluation of Lactobacillus rhamnosus strain GG, a potential probiotic in dogs
I'll add more as I come across them at a later date.