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Nutrition Nuggets
Your dog's nutrition is important for a healthy & happy life. petMD experts help you to know what to feed your dog, how much food to feed, and the differences in dog foods, so your dog gets optimum nutrition.
Nutrition Nuggets is the newest offshoot of petMD's Dog Nutrition Center. Each week Dr. Coates will use her expertise and wisdom to blog about the intricacies of dog nutrition.

Pro- and Prebiotics - What are They and What Do They Do?

November 11, 2011 / (17) comments

Probiotics are all the rage. Numerous nutritional supplements, and even foods like yogurt, contain these live microorganisms (bacteria and/or yeast) that can provide health benefits when given to an animal or person. We tend to think of probiotics when considering gastrointestinal health or disease, and they certainly do play an important role in this regard.


Take a dog with diarrhea, for example. Whatever the cause — stress, dietary indiscretion, infection, antibiotic therapy, etc. — the diarrhea sometimes persists even after the inciting issue has been handled. This often results from an imbalance between the microorganisms in the gut that promote normal function and those that secrete toxins or are otherwise disruptive when they are present in larger than normal numbers. Probiotics are a way of boosting the number of "good" microorganisms that are present, thereby helping them out-compete the "bad" ones.


It also appears that probiotics may work in other ways. They seem to be able to beneficially modify immune function. Studies have shown that probiotic supplementation can help treat infections outside of the gastrointestinal tract as well as some types of allergic or inflammatory diseases. This isn’t too surprising considering that a large proportion of the body’s immune system is associated with the gut, so anything that influences the immune system could provide a more wide-spread effect.


One downside of probiotic supplementation is that the microorganisms aren’t able to effectively stay and reproduce within the gut for long periods of time. This isn’t a huge issue when you are dealing with an acute illness, say diarrhea associated with antibiotic use, but for chronic disorders probiotic supplements need to be continued long-term to reap the maximum benefits.


This is where prebiotics come into the picture. Prebiotics are non-digestible ingredients that support the growth of probiotic microorganisms that either reside in the gut naturally or are added via supplementation. Think of prebiotics as a way to preferentially feed the "good" microorganisms in the gut, giving them a potential advantage in their competition with the "bad" microorganisms.


Beet pulp is a commonly used prebiotic in dog foods. It is a type of carbohydrate that undergoes partial fermentation within the gut to provide food for probiotic microorganisms. Feeding your dog a food that contains a prebiotic like beet pulp is an easy way to support gastrointestinal health, add fiber to the diet, and promote overall well-being.


Look at the ingredient list on the dog food label to determine whether or not beet pulp is included. It does not need to be present in large amounts, so finding it approximately half-way down the ingredient list is perfectly appropriate. I recommend new Hill’s Science Diet Ideal Balance, which contains a proper proportion of beet pulp in every serving. Lastly, use the MyBowl tool and the guaranteed analysis on the food label to determine whether or not carbohydrate levels as a whole are appropriate and in balance with other nutritional categories.


Dr. Jennifer Coates


Image: blanche / via Shutterstock

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Comments  17

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  • Acidophilus
    11/11/2011 04:19pm

    I'm a firm believer in supplementing humans and critters with acidophilus any time antibiotics are on the menu. It's saved lots of trips and phone calls to the vet.

    I once had a doctor prescribe antibiotics to me. As he handed me the script, he said that if I had any diarrhea to give him a call and he'd call in another script. I smiled sweetly and told him that if that happened, I'd just take acidophilus and the problem would be resolved.

    He said, yup, that would take care of it. The odd part was that he looked at me like I was a genius.

    No genius here. It just makes sense. Antibiotics kill bacteria. It does not discriminate between bad bacteria causing the problem or the good bacteria needed to digest food in the intestinal tract. Acidophilus replaces the good bacteria.

  • PREbiotics? not for dogs
    11/12/2011 04:36pm

    Probiotics are great to use in periods of stress or when natural flora is killed off by antibiotics, but I'd have to disagree with you on the usefulness of PREbiotics for dogs. Dogs have a short digestive tract, food stays in the stomach for a relatively long time, but moves through the intestines rapidly. The longer time in the stomach is to facilitate digestion of their natural diet which is primarily protein.
    Dogs do not ruminate their food, they don't have multiple stomachs like herbivores, and food does not stay in the digestive tract long enough to ferment. This is just a line fed to us by the commercial dog food companies to justify their use of cheap fillers at the expense of the quality meats that should be the mainstay of any dog's diet. Bone acts as the dog's natural source of bulk to firm the stool. That being said, since commercial kibbles don't use bone, then they do have to provide some sort of bulking substance like beet pulp etc. It's just that these types of diets are suboptimal and unnatural. I personally like a frozen ground raw diet that is made by Bravo. To that I add Vitamin E, fish oil and the occasional dose of probiotics.

  • 11/12/2011 10:27pm

    Actually, beet pulp is one of the best fermentable fibers, (bulk, prebiotic, whatever you name it), supported by scientific data over 10 years ago. The Iams symposium books have a couple of good papers on this. Bone has nothing to do with fermentable fibers which are the lignins found mostly in plant based ingredients. There is a great website on this for cats, that also applies to dogs at http://www.felineconstipation.org

    I am not sure where your information is being drawn from, Geneva, but I certainly am not familiar with any data supporting your comments. Please can you find reference material that uses scientific data so that we can decide for ourselves based upon the data?

    Thank you in advance for your efforts to respond to this in kind.

  • 11/13/2011 04:11pm

    I've done extensive personal reasearch on canine nutrition and have a four-part series on my website. http://mysite.verizion.net/coatcloset. (look in the articles section). Dr. D.S. Kronfeld did extensive research on canine dietary requirements in the 70's and was among the first to question the high fiber and carb components of commercial dog diets. The best of the new books is "Raw and Natural Nutrition for Dogs" written by Lew Olson, PhD in natural health and specialist in canine nutrition.

    It’s not surprising that a dog food company would promote beet pulp in their foods. Beet pulp is an economical, cheap filler. The reasons companies give for including beet pulp in dog food include: (A) bulk to the stool and (B) to support beneficial bacteria. Bone is what gives bulk to the stool in a dog’s natural diet. As to point (B): Neither bone nor beet pulp are useful to support the growth of beneficial bacteria in dogs.

    Beet pulp was first added to livestock feed for horses and cows, as a bulk-forming additive. Ruminants can make use of fermentable foods, but dogs can’t make use of fermentable foods, because their intestinal tract is short and sweet. Anything they eat passes through quickly. The colon of the dog is quite short and food doesn’t remain in there long enough to ferment. Again, other than providing a means of bulking the stool, beet pulp is useless for dogs.

    Bone is the natural bulk-forming ingredient in the canine diet, so dogs eating sufficient amount of bone don’t need any beet pulp to bulk and firm their stools. Beet pulp has no nutritional value. It does produce more stool volume, so if you want more poop, by all means feed a food with beet pulp.

    Beet pulp is also high in oxalates, substances which impair calcium absorption. So instead of dogs eating a diet containing bone, their natural source of calcium, we give them a high phosphorus diet and add beet pulp, and then add in more calcium to attempt to balance out this very unbalanced, unnatural diet. Not logical or sensible at all!

    If a dog is in need of probiotics, they are available in animal-based products like yogurt or acidophilus capsules, so why bother with the leavings of the sugar industry unless you are a manufacturer who just wants something cheap to serve as a filler in your commercial food?

    Good Grief. You'd think that dogs would have died out thousands of years ago without man filling them up with beet pulp and assorted other unnatural dietary ingredients. If faced with a nice bowl of beet pulp versus a nice meaty rib bone, which would they choose?

    Other commonly-used pet food ingredients that are actually harmful to dogs include soy and flaxseed. A whole ‘nother ball of wax on that subject….

  • 11/13/2011 04:51pm

    Don't waste my time with your lectures if you can't provide references to data that proves what you say, please? The research I have paid for out of pocket and actually assessed, as a former research assistant, states otherwise. Anyone who claims that what I state is incorrect is expected to provide the science as I am when asked.

    We aren't talking about our companion animals' wild ancestors but precious pets that we have changed to conform to our needs,
    Here is a freebie for you as far as the science goes: http://jn.nutrition.org/content/128/12/2717S.full.pdf+html
    and then this next study, just out, (you have to pay for it), essentially says as the end summary that ALL forms of processing provide the same nutrition, except that extruded has looser stools, which are needed for our sedentary house pets that have had gonadectomies and lack of physical expenditure, and literally, (to use Deb Zoran's words), been plunged into menopause: http://jas.fass.org/content/early/2011/10/14/jas.2010-3266.full.pdf That study is supported by comparison of equal cuts, equal portions, of meats compared on nutritiondata.com.

    However in our world, with altered pets, "raw" is way too high in calories for good nutritional health, and we like having pets with healthy weight and no nutritional illnesses. We select low calorie choices that have fat rendered off. This also drops insulin resistance as the excess fat contributes to that. Based upon science, another criteria for us is that either beet pulp or rice bran is in the dry foods as the best sources of fermentable fiber - according to science, and the pets are fine, all of them.

    Whoever taught you that bone is a fermentable fiber, I suggest you track them down and get your money back.

  • 11/13/2011 05:10pm

    "Whoever taught you that bone is a fermentable fiber, I suggest you track them down and get your money back."

    Whoever taught you reading comprehension, please track them down and get your money back. Re-read what I wrote. I've responded to you twice now, and neither time did I suggest that bone is a fermentable fiber.

    And yeah, mass sterilization of our pets is a poor idea. The least of the prolems resulting from that mentality is obesity. That's why in Norway it is illegal to neuter your pets without medical necessity.

    I'm sorry that a discussion with logic, facts and truth is so threatening to your self-esteem that you feel the need to lash out at me. I have provided plenty of references at the end of my series, which is available on my website. Swallowing the lines fed to you by dog food companies, the very entities who make money by promoting poor-quality ingredients in foods? Very sad.

  • 11/13/2011 06:13pm

    I presume that means you don't have scientific references to back your statements. Dr. Coates' article above does have several studies with data to prove what she states, such as the data at the URL I posted earlier in this dicussion. End of discussion.

  • 11/13/2011 06:30pm

    So, you are or are not Dr. Coates? Odd that you are presenting yourself as she and then in the next post, speaking about her in the third person.
    I have provided many references including one that was posted here earlier today; a study done on a few dogs that demonstrated that beet pulp may increase levels of probiotic flora in some dogs, but not others. Incidentally, they claim this is the FIRST study of this kind done.
    I checked Dr. Coates's posted reference and it involved dogs with special needs i.e. IBS and colitis. And a good portion of her dietary concern seems to be with dogs who are unwisely neutered. Perhaps we should think twice about jumping to sterilization, with its many attendant health risks, instead of foisting a diet of processed garbage on our pets in a lame attempt to correct the health problems we are creating via castration. Food for thought.

  • 11/13/2011 11:13pm

    Quote: "Beet pulp is also high in oxalates, substances which impair calcium absorption."

    Just to keep facts straight, here, it is easy to look online and find that beet LEAVES contain oxalates, not beet pulp ; However, beet pulp does have calcium in it. Foods that actually contain a nutrient also have micronutrients that help in the digestion of the nutrient itself, which is why whole foods are better sources than supplements:

    Gut bacterial activity feeding on a suitable substrate enhances calcium absorption. As previously stated, this site, shows beet pulp and rice bran to be the most appropriate fermentable fibers or substrates, (see Table 6, page 2720S)and they will do a great job of improving absorption of all nutrients that a dog or cat needs. Dr. Coates information will have come from other such studies as well. Her information is well written and sound.
    and Small Animal Clinical Nutrition is quoted at peteducation: They also provide substantial references.

  • 11/13/2011 11:30pm

    Sorry the URL's did not take above. The website discussing beet pulp composition are here:
    and http://tinyurl.com/d9br5he

    The reference to Table 6 was at: http://jn.nutrition.org/content/128/12/2717S.full

    And other websites showing a sample of just how much science has accumulated over the years was found through these sites:

    http://jas.fass.org/content/73/4/1110.full.pdf and peteducation's site: http://www.peteducation.com/article.cfm?c=1+1399&aid=2705


  • 11/14/2011 01:33am

    Thanks for the list of references. I am always interested in learning more about nutrition!
    While beet pulp is not as high in oxalates as the greens, it is still a source. Here's a study that references the presence of oxalic acid in beet pulp. (Greens have 0.61 gm per 100 mg serving, so yes, they are much higher)

    Spinach, greens, beets, some grains etc that are naturally high in oxalic acid are also often high in calcium, although bioavailability is limited by the natural binding activity of the oxalic acid to the calcium....well, I'm sure you already know all that.
    It's just generally a greater concern with plant products, although organ meats are also a source of oxalates.

    The nutrition textbook you referenced is produced by the Mark Morris Institute, which also brings us the Science Diet products. Mark Morris was a wonderful philanthropist; he founded AAHA and was president of AVMA at one point I believe. His Morris Foundation continues to make a positive difference for animals.
    He is known for promotion of nutritional courses in veterinary schools. It is possible that some of the information presented in the textbook may contain inherent bias toward commercial foods. The food companies fund much of the research. While that does not mean the research is invalid, it could mean that certain subjects more important to food produced receive more emphasis while other types of subjects go unexamined. Commercial influence is pervasive in society, one of the unfortunate byproducts of an otherwise desirable capitalist free marketplace. Just something to keep in mind as we sort through the information that is available.
    Not trying to be testy, LOL but I took my first college nutrition course in 1977. It's always been a subject of great interest to me.
    Best regards, Geneva

  • Dog's digestive system
    11/13/2011 04:22pm

    Most of us think of diet needs for a dog being similar to ours, however, that is not really accurate. The dog's digestive system is geared toward digesting high protein and high fat diets. Carbs and fibers are of limited value. Food remains in the dog's stomach a relatively long time, so that the high-protein fare can have adequate exposure to pepsin and turned into chyme. Then once the food enters the short intestinal tract, the nutrients are quickly absorbed and what remains passes through quickly. The high acid content of the dog's GI tract also serves to kill most harmful bacteria naturally...hence, why they can eat rancid foods and feces and not become ill from them. Dogs do not have amylase in their saliva, but they do produce small amounts of dietary amylase (unlike cats) so small amounts of simple carbs can be digested OK. However, they cannot digest complex carbs, which mostly pass through undigested.
    Well this is probably more info n nutrition than most people actually care about....ttyl!

  • 01/10/2012 07:37pm

    "...but they do produce small amounts of dietary amylase (unlike cats)..."

    Do you mean *pancreatic amylase? Dogs and cats both produce pancreatic amylase (see work of Ellen Kienzle). And they are both quite capable of digesting and absorbing carbohydrates in a variety of forms (again, Kienzle as well as Morris, de-Oliveira, and Fahey among others), although digestibility is higher with cooked/processed forms, just like in people.

  • 01/12/2012 02:09am

    Yes, typing too quickly, I meant pancreatic amylase as opposed to salivary amylase. Dogs do not produce salivary amylase, so they do not digest carbs as well as humans do. Due to the lack of salivary amylase, and the properties of food that is not well-masticated, the carbs in the diet of the dog do not begin the process of digestion until reaching the small intestine. The small intestine of the dog is relatively short in comparison to the human small intestine, and the small intestine of the cat is even shorter than that of the dog. Yes, they have an ability to digest carbs but are better equipped to digest a high-protein, moderate fat diet.
    In a comparison study of lab animal GI anatomy, dogs and pigs showed the most rapid transit from the GI tract. "The total GI transit in humans is around 20-30 hours. Beagle dogs have substantially shorter transit times, 6-8 hours....The digestive system of the dog is relatively short and simple." (Kakarli). Longer transit times overall are needed for optimal digestion of carbs. Interestingly, the dog colon is non-sacculated which further speeds transit time. Other lab species may have more capacious hindguts to assist with fermentation of complex carbs. Humans have a poorly defined cecal region, and the vestigial appendix is what is left as our diet has trended away from raw vegetables and fruits to cooked foods including meats and grains. The cecum of the dog is also a lateral appendage! The stomach of humans and dogs is considered similar in morphology and emptying characteristics. So we do have some GI similarities with dogs but also some significant differences. The short GI transit time in dogs is not conducive to carbohydrate digestion, unless, as you noted, the food is heavily pre-processed.

  • 01/12/2012 02:32pm

    “Dogs … do not digest carbs as well as humans do.”

    I’m not sure that has been compared. Can you post a reference for that?

    Part of the problem, and this goes for the GI transit as well, is that you cant directly compare different studies unless conditions are similar. GI transit in particular is problematic in that many factors influence this rate, including meal size, meal composition, fat level, fiber type, fiber level, particle size, etc etc. Researchers don’t use standardized ‘test meals’ to study this in animals, so inter-species comparisons are not accurate, not to mention the inter-individual differences in transit time depending on conditions.

    “… the carbs in the diet of the dog do not begin the process of digestion until reaching the small intestine. “

    True, but we know that the activity of pancreatic amylase varies with diet type and adaptation, so again, the conditions of the study can influence the findings. Also, not all carbs are equal, of course. You cannot compare the results of one study using one carb type/level under one set of conditions to another using a different carb type/level under differing conditions.

    “The small intestine of the dog is relatively short in comparison to the human small intestine, and the small intestine of the cat is even shorter than that of the dog.”

    Well, again, there are limitations in comparing species here. One issue is that length is but one factor. Surface area (ie absorptive surface of the inner intestine or mucosa) is a very important factor, and this differs among species significantly (to give an idea of order of magnitude, the the cat has approximately 6 times more mucosal area than the rat per unit of serosal length. Which brings up another factor: what basis is used for expression of these values? Do you compare intestinal length per body weight, surface area per body weight, or surface area per intestinal length, or other??

    “ The short GI transit time in dogs is not conducive to carbohydrate digestion, unless, as you noted, the food is heavily pre-processed.”

    I’m not sure this has been established with any certainty. Even cats can efficiently digest carbs (>94%), when provided as ground or cooked starch. Most foods in most species, including humans and other omnivores, see improved digestibility when cooked (not sure I would refer to this as “heavily pre-processed”). I wish things were more straightforward, but science is sometimes messy. ;)

  • Colitis and IBS treatment
    11/13/2011 05:29pm

    Thank you so much for the link to the article on the dietary treatment of IBS and colitis. I'm going to add it ot my collection of references.

  • Study-beet pulp, dog diet
    11/13/2011 05:58pm

    Here's a recent study about the influence of prebiotic fiber on the flora of the colon. It's a small study on just six dogs but interesting nonetheless. Firmicutes (including the lactobacillus genus) are generally increased with inclusion of beet pulp in the diet, but "the changes were not equally apparent in all dogs". This will be an interesting are to follow in future research.





Photo of Jennifer

... graduated with honors from the Virginia-Maryland Regional College of Veterinary Medicine in 1999. In the years since, she has practiced veterinary medicine in Virginia, Wyoming, and Colorado. She is the author of several books about veterinary medicine and animal care, including the Dictionary of Veterinary Terms, Vet-Speak Deciphered for the Non-Veterinarian .

Jennifer also writes short stories that focus on the strength and importance of the human-animal bond and freelance articles relating to a variety of animal care and veterinary topics. Dr. Coates lives in Fort Collins, Colorado with her husband, daughter, and pets.

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