Probiotics For Dogs with Sensitive Stomachs

The marketing is robust; the evidence - lacking.


Denise Serls of Stewart, Florida, was concerned. Her four-and-a-half-year-old goldendoodle, Harlii, kept having diarrhea and loose, unformed stools. “Someone suggested I try a probiotic,” she says, “telling me it would keep his stomach more relaxed. But I don’t really see any difference.”

Veterinary researchers aren’t surprised. The evidence behind currently marketed probiotics, supplements that contain supposedly “good” bacteria to help an overactive or “sensitive” gut adjust, is “pretty limited,” says J. Scott Weese, DVM, DVSc, DACVIM, an internationally renowned microbiology researcher at the Ontario Veterinary College in Canada’s University of Guelph. Adds Jan Suchodolski,,, PhD, DACVM, another heavy hitter in the field, while there are “many studies in humans, in dogs there are maybe only about 10. We just don’t have good clinical research.” Moreover, comments Dr. Suchodolski, who serves as associate director of the Gastrointestinal Laboratory at Texas A&M University’s Department of Small Animal Clinical Sciences, “the quality of most products for sale is very poor.”

Indeed. When Dr. Weese analyzed 25 canine probiotics available in regular retail outlets, 10 did not even list the bacterial counts in their merchandise. Of the 15 that did, only one in four actually contained what the label said. Some products mentioned that they contained bacteria that don’t exist; that is, they made up or misspelled bacterial names. Other problems: no growth of the bacteria supposedly in the supplements, bacterial counts that were too low to effect any beneficial change in the gut, and no expiration date. In the end, only two products out of the 25 met the criteria Dr. Weese looked at for quality control. His research was peer reviewed and published in the Canadian Veterinary Journal.

“A huge problem is that without FDA regulation, anybody can throw anything on a label, and it may or may not have something to do with what’s inside the bottle you just paid $40 for,” says Craig Webb, PhD, DVM, DACVIM, the head of the Small Animal Medicine Section at Colorado State University’s Veterinary Teaching Hospital.

No FDA regulation? Not really, or at least not in a way that becomes terribly meaningful for consumers. In the United States, probiotics are considered what’s called a nutraceutical rather than a drug; they are over-the-counter supplements. So the standards for getting them to market are comparatively lax. It’s essentially an “unregulated industry,” says Dr. Weese, “which makes it ‘buyer beware.’ Some products contain what they say they do, and probably most don’t.'” The marketing is way out in front of the standards for good manufacture and clinical research.

It’s different in Europe, Dr. Suchodolski points out. “In the European Union,” he says, “the term ‘probiotic’ has even been banned from marketing. The countries in the EU say the term has become so branded that in itself it implies a health benefit even if one hasn’t been proven. And in the last five years, only a handful of probiotic products have been approved for sale to the public because of insufficient proof of their health claims.

It’s the same for products marketed on this continent. There are no published studies demonstrating a positive health effect for most commercially available products. When companies say a product works, ‘It kind of presents results extrapolated from other products — products used in clinical studies but not the one they are selling,” Dr. Suchodolski says.

It often comes down to specific bacterial strains. People may have heard that Lactobacillus bacteria are good, or Lactobacillus acidophilus, but acidophilus is just a species of bacteria in the Lactobacillus genus. When researchers examine possible effects of certain bacteria, they are looking at specific bacterial strains, and the strain in a product on the market may have nothing to do with the strain used in scientific research that showed a benefit. It’s like holding up a grapefruit and saying it’s a lime because they’re both citrus fruit. Consider that some E. coli are perfectly harmless to a mammal’s intestine. But certain strains, like E coli 0157:H7, can, and have, caused kidney damage and even death. You’ve no doubt heard about it on the news from time to time. It’s the “0157:H7” that tells the story, not the “E. coli” designation.

Is There Any Value to Feeding Dogs Probiotics?

With so much lacking as far as the probiotics on the market, you might be asking yourself whether there’s any legitimate scientific inquiry into the possible benefits of probiotics at all. The answer is yes. It has now been shown that there are about 100 trillion bacteria in the mammalian GI tract, and they are made up of about 1,000 or more different species, each with very particular strains. And “there are some bits and pieces of evidence that probiotics might work” in ameliorating certain gastrointestinal, shall we say, “situations.” The basic thrust is that if you flood the gut with hundreds of millions of “good” bacteria, if not more, they crowd out so-called bad ones or change the ratio of various microorganisms so that the large intestine has an easier time passing fecal waste through — not too slow, not too fast.

When scientists look at possible applications for bacteria they believe may be turn out to prove beneficial, they isolate specific strains and first test them in vitro (meaning in test tubes or petri dishes), then perhaps in small laboratory animals such as mice, and then in larger mammals, like dogs or people. The research so far indicates that certain probiotics may be able to ameliorate constipation, while others cut down on stress-related diarrhea. There is also some evidence that certain probiotics can help stem acute diarrhea — diarrhea that comes on suddenly, in a bout, and has nothing to do with stress.

But there are caveats — lots of them. One, says Dr. Suchodolski, is that “nothing is guaranteed. Every single individual, whether a dog or a person, is different. We all have similar groups of bacteria in our GI tracts, but the proportions are somewhat different.” So if you want to give something to regulate your pet’s bowel movements, the response is going to differ from pet to pet. And in no case does it appear that the response will be great in magnitude.

“While clinical studies have shown statistically significant improvements,” Dr. Suchodolski explains, “the effect may be on the order of something like 10, 20, or 30 percent.” Thus, even if your dog responds 30 percent better than he would on a placebo, that very well might not always look like a huge improvement to most pet owners.

Another issue is that so much of the research has been conducted on people and then extrapolated to make recommendations for dogs, even by the few reputable companies who make probiotic products with good quality control. There’s very, very little on specific amounts of probiotic therapies for dogs with various GI issues — or even whether they work as well as some appear to in humans.

Complicating the matter more, for any species, is the fact that it’s often not clear what has caused a dog to have diarrhea — an infection, a food that had a contaminating bacteria, something else? It’s not always easy to work backwards from a problem to a solution if you can’t ascertain the origin of the problem.

For instance, we suspect that with Harlii, the goldendoodle from Florida, the problem is an allergy, either to something in the environment or to something in his food. He scratches at his skin and also is prone to ear infections — a problem that frequently goes hand-in-hand with allergies. Moreover, he is fed a raw food diet which, because the meat is not cooked, may contain harmful bacteria of its own that could be causing him gastrointestinal upset. Checking for and treating any allergy that might be present along with getting him off raw food is probably going to do much more for his difficulties with his bowel movements than any probiotic could.

Even with so many causes of GI problems, though, and so many other variables, none of the researchers we talked to are completely against dog owners’ trying certain products on the market.

Perhaps the “strongest evidence,” says Dr. Suchodolski, is for “stress diarrhea. If you know your dog is going to be boarded,” for instance, and that causes him a lot of stress that leads to loose, runny stools, it is not unreasonable to consider administering probiotics to him. “Preventative is probably better” than “during,” he adds. “If you can anticipate a stressful event, start giving the supplements a few days to a week ahead.”

For an acute onset of diarrhea not related to stress, Dr. Suchodolski advises perhaps trying a probiotic on your dog either “that day or one day later.” The bacterial counts in the gut need to be affected as soon as possible after the problem is detected. It takes time for the intestine to respond to the change in bacterial ratios.

There are also “some bits and pieces of evidence” that probiotics might work for constipation, Dr. Suchodolski says. For chronic diarrhea, as opposed to diarrhea brought about by stress or an acute bout that comes and goes, studies have shown an effect “in cats but not dogs.” Research simply hasn’t yet looked at dogs in that situation yet with regard to probiotic products.

Dr. Weese agrees that giving probiotics to a dog who is having problems with bowel movements is a not unreasonable idea — as long as you have gone to your veterinarian to make sure the dog’s GI upset isn’t due to something that can be traced with traditional diagnostics and fixed with medical therapy. The “limited evidence” for a beneficial effect from probiotics may make them worth a try, he says. For the better products out there, he comments, “while we still don’t have really good data on how they work and how well they work, at least we know the bacteria are going to make it into the dog,” past the harsh acid in his stomach and into the intestine. And, he adds, “probiotic therapy is in general very safe unless the dog is a newborn” with an immature immune system. The “downside is money,” he comments. “To a certain degree you have nothing to lose but a few bucks.”

Which Probiotics to Choose for Your Dog?

With research that highlights the dismal lack of quality control that goes into the manufacture of most probiotic products — too few bacteria, incorrectly labeled bacteria, no information on bacterial strains — how do you decide which probiotic product to purchase for your dog if you’re inclined to give probiotics a try?

Fortunately, researchers are in general agreement that there are four products on the market that, while evidence for their benefit is scant, are produced with reliable quality control. What’s said to be in the supplement is actually in there.

The two products that passed the quality control test in Dr. Weese’s research are FortiFlora, made by Purina; and Prostora, put out by Iams. Dr. Suchodolski also says those two are well made and “have some science behind them.” He recommends as well Proviable, manufactured by Nutramax, and VSL#3, from VSL Pharmaceutical. The latter is not a veterinary product, but “in human medicine, it has the most study behind it,” Dr. Suchodolski says. “There have been 120 studies in the human field. In veterinary medicine, there has been just one study, not yet published.” Still, he opines, because the chances for harm are so small, it might be worth a try.

But, he points out, for any of the four products with decent quality control and some research behind them, “it may work well, it may work a little bit, and it may work not at all. I’m optimistic that [using probiotics with good quality control] will be a useful approach. But we still don’t know which products are right for which diseases for which animals. It is an impossible task” at this point, “even for veterinarians to distinguish the science from the marketing.”

Dr. Weese sees it the same way. “I wouldn’t steer people away, but I wouldn’t get their hopes up. There are a lot of things that have to come together for a probiotic to work. It may work in some dogs, but we don’t know in what dog at what dose. If your dog happens to be one that responds, that’s great. If not, move on.”


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