Updated: Feb 29
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I wrote this ode to poop inadvertently when writing a quick note about dog food digestibility. So let’s start there. This is a longer post, and I thought about breaking it up, but it provides a much more cohesive picture when kept as one piece.
NOTE: There are some photos of poop in this post and some graphic descriptions, so if you don't like those, you may not want to read this.
Digestibility is how much of a food or nutrient is retained, and how much is expelled (basically, how much is crapped out).
Digestibility is a complex issue, and there are 2 problems when evaluating dog food digestibility:
AAFCO (the organization that sets dog food standards and requirements) does not require digestibility studies
Companies that perform digestibility studies all do it differently and also evaluate different digestibility parameters.
So that means that even when companies evaluate digestibility, it's often like comparing apples to oranges since there's no standard or definition for doing so.
So what do we do? Well, here's what I do.
I look for a company that I consider reliable, ethical, honest, and responsible.
I look for transparency. Avoidance of a question is a red flag for me.
I look for a company that goes ABOVE AND BEYOND what is required to ensure the best possible and safest product.
I look at results in my dogs and puppies
I look at poop!! Poop is often the proof of digestibility!
Since digestibility studies are not required by AAFCO, dog food companies don't have to perform them, and, if they do perform them, they don't have to tell us. So I got a wild hair one day and decided to contact a number of companies to find out 1. do they perform digestibility studies 2. will they tell me, and 3. what those studies show. Please note, this is a completely unscientific survey, I didn't contact every company out there, and some of the editorial comments are my personal opinion only and not necessarily based in any fact. These contacts were made in early July 2019. I would welcome any additional information if anyone has any.
Here's a summary of information I received, some through email and some via web pages:
Acana Heritage and Singles—"over 80%"
Acana Regionals—"high 80s"
Annamaet—"mid to upper 80s"
Earthborn Holistic—Information not given when requested
Eukanuba—Information not given when requested
First Mate Whole Feed Combined—75%
Fromm—"at least 85%"
Hills—Information not given when requested
Life's Abundance—Do not test for digestibility
Nature's Variety—"low to mid 80s"
Nutrish—Information not given when requested
pawTree—Minimum 83%. On average digestibility of protein is 87% and digestibility of fat is 94%. Average calories digested 89%
Purina—Information not given when requested
Royal Canin—Information not given when requested
Solid Gold—"high 80%"
Taste of the Wild—86-88%
Wellness Complete Health Dry Dog—82-87%
Wellness Core Dry Dog—84-87%
Wellness Simple Dry Dog—82-84%
Zignature—Information not given when requested
Here are screen captures of my sources. Some, but not all, contain additional information.
So Let's Talk Poop
What is poop?
In a nutshell: Poop is what's left of food after nutrients have been absorbed by the digestive tract.
Understanding how food is digested helps us to understand the nature of poop and what factors may be causing undesirable changes in poop.
Chewing. Food enters the mouth and is chewed. Human digestion starts in the mouth, but canine digestion does not.
Swallowing. Esophagus. Food is swallowed and moved from the mouth to the stomach. No digestion occurs at this point either.
Digestion. Canine digestion starts in the stomach. Food is mixed with stomach acid and proteins begin to break down. Canine stomach acid is even more concentrated than in humans, which is one reason that dogs have less susceptibility to pathogens than we do. (Think about it, we would get horribly sick if we ate some of the things dogs eat, including raw meat, rotting food, or feces, and regularly licked butts as a greeting.) Food spends more time in the stomach of dogs than in humans, as much as 10+ times longer. Food, now called “chyme,” moves from the stomach to the small intestines through a process called “peristalsis,” which are kind of little waves in the intestinal wall that moves food along. Digestive juices, including enzymes produced in the pancreas and liver, continue breaking down food, and this is where starches and other carbohydrates begin to be digested, in addition to proteins. As food breaks down, nutrients are delivered into the blood stream through the gut wall. Contrary to the opinion of some, dogs produce the enzyme amylase, which is the enzyme that digests starches. Also contrary to the opinion of some, wolves produce amylase and can digest starches. However, wolves produce much less amylase and studies have shown that since dogs co-evolved with humans, including eating our food, that is reflected in the increase in amylase in dogs (versus wolves). [1, 3-5]
Stool production. Waste products—substances that can’t be “harvested” by the gut for energy or nutrition—accumulate as food passes into the large intestine, forming stool, which is then excreted (pooped out), hopefully in solid form. Bacteria in the large intestine perform a last digestive step, harvesting the last bits of nutrition and energy from the food.
Looking at this process, you can get a better idea of what digestibility is and why stool is a good indicator of digestion or digestive problems.
Some poop facts:
Dog poop is usually about 65-75% water.
After water, the next largest component of poop is bacterial mass. This includes both living and dead bacteria and can easily make up as much as half, or more, of the dry content of poop.
After bacteria, the dry content of poop also contains undigested food remains, including fiber and other carbohydrates, protein, fat, and even dead cells that sloughed off the walls of the GI tract.
Lastly, there are minute amounts of metabolic waste. The characteristic brown color of poop is mostly caused by something called “stercoblin,” which is made of broken down bile and red blood cells that are being excreted.
Also, if your dog eats something it shouldn’t you may very well see that in the poop.
What do I look for in poop as indicators of health, digestion, and food quality?
Color, consistency and firmness, odor, volume, and how easily it is passed (diarrhea vs normal vs constipation).
What can poop tell us?
Poop should be dark brown. Slight variations are normal and depend on food, individual digestive systems, individual microbiomes, etc.
Sometimes color is simply reflective of what has been eaten. Dogs fed raw with high bone content have crumbly white poop. Beets can turn poop red, carrots and sweet potato can turn it orange, greens can turn it green, blueberries can turn it black, etc. Food coloring can also change poop color. Neonatal poop while mother's milk is the primary food will also be a different color and consistency.
Assuming none of the above benign color changers are a factor, there are times poop can indicate (but doesn't always mean) problems. Before panicking, be sure your dog didn't eat something that could change poop color.
Light colored poop. Assuming your pup isn't nursing or your dog isn't eating a high bone content raw diet, lighter colored poop can indicate problems with the renal system, from inflammation in the liver, pancreas, or gall bladder to problems with bile ducts.
Red poop. Red poop is most commonly caused by bleeding lower in the digestive tract (usually large intestine, rectum, or anus). It can be caused by parasites, constipation, inflammation, obstruction, or tumors/cancers.
Black poop. Black poop can indicate bleeding higher in the digestive tract (usually stomach or upper small intestine) and is sometimes seen when there are digestive tumors.
Consistency and firmness
I’m always looking for poop in the Goldilocks Zone—not too firm and not too loose—juuuuuust right!
Healthy human poop is a little looser than healthy dog poop. In dogs, you want to see a “Tootsie Roll” shape, color and firmness, but you don’t want it so firm that it’s hard to pass (constipation).
The poop emoji we all know and love is a good example of healthy consistency for human poop, but is a little on the loose side for what we want to see in dog poop. This is a borderline consistency for me, not quite as good as I'd like, but also not anything I'd worry too much about (although I still like to see firmer poop).
Firmer poop has a purpose for dogs—firm poop expresses the anal glands each time it passes.
This prevents build-up of fluid in the anal glands. Anal gland contents add to the odor of stool.
Dogs are predators and, as such, mark territory using their anal glands. They also express their anal glands when frightened or anxious. If we had noses like most animals that can actually tell us more than if dinner is being made or if we are near a sewage plant, then we would be able to “read” the scent information from anal glands to learn things about the producer such as sex, health, age, reproductive status, and probably more than we nose-blind humans can even imagine.
Normal anal gland contents are clear to yellow-brown and fluid.
Impacted anal gland contents are brown and thick.
Inflamed anal gland contents (“anal sacculitis”) are yellow to yellowish green and thickness is between normal and impacted consistencies
Abscessed anal gland contents are reddish brown with pus and are the stinkiest of anal gland contents.
Food quality is the number one factor impacting anal gland contents. There’s also the possibility of a physical defect causing the problem, but this is less common.
Dogs that scoot their butts on the floor may be having anal gland discomfort (parasites are another cause of this behavior).
A healthy dog should NOT need its anal glands expressed manually, and I discourage this service, commonly performed when dogs are groomed, when not required for medical reasons, as it encourages dependence on manual anal gland expression.
Fun fact: Humans have anal glands, too!
Constipation occurs when poop is so hard and dry that it becomes hard to pass. Constipation in young puppies can be considered a medical emergency if not resolved very quickly. Causes of constipation include low fiber, dehydration, lack of physical activity, and sometimes some medications or supplements can cause constipation.
Loose poop in dogs is anything not firm. So “soft-serve ice cream” consistency is considered a little loose. Diarrhea or even just brown water are the more extreme forms of loose poop.
There are a LOT of causes of loose poop. Just a few include:
Bacterial infections or overgrowths
Low quality food
Low digestibility of food
Too much dietary fat
Too much fiber
Assorted diseases and GI issues
Impact of dietary change
Loose poop is often associated with changes in the diet of a dog that occur too quickly. This is an interesting situation, and one I feel is very, very often misunderstood.
Current science is showing pretty clearly that dogs co-evolved mutualistically with humans as scavengers that associated with our encampments and small societies. Roughly 5,000-20,000 years ago it began, with dog serving us by helping to clean up items that would otherwise go to rot and attract pests and scavengers, alert us to some dangers, and us serving dogs by providing an easy food source as well as some protection due to our numbers, our campfires, etc. [1,3-5].
Ok, you're saying. That may be interesting, but what does it have to do with this poop talk? Well, think about it. That means that dogs evolved to eat ALL kinds of foods at different times.
So what happened with modern dogs in the last 100 years or so that dogs can't handle food change easily? The answer is: monodiets (eating the same thing all the time) promoted by commercial dog food companies, starting sporadically in the 19th centering and becoming more mainstream in the 50s and 60s.
When a dog eats the same thing every day their digestive system becomes adjusted to that diet. That means enzyme production, and, more importantly, the bacterial flora that live in their gut. Bacterial that can thrive on that particular diet survive and takeover, and others die or just end up in very small numbers. So when a new food is introduced, there needs to be an adjustment of the bacterial balance in the digestive tract. This can cause flatulence, stomach upset, and diarrhea.
On the other hand, when dogs are fed a diverse diet, they have a more robust and diverse microbiome that is very flexible and can more easily adapt and handle changes in food.
If poop is known for one thing, it’s a distinctive and often revolting odor.
But odor can tell us more than whether we need to clean or just get away from the scene of the crime.
Healthy dog poop should have a distinctive, but relatively mild, odor. The most common culprits for foul odor in dogs and puppies are parasites and low quality food.
You’ll hear raw feeders often talk about how their dog’s poop doesn't stink. While there can be downfalls to raw feeding (another topic) and it’s certainly not for everyone, there’s no denying that raw food is highly digestible and in fact often does result in poop with very little odor. As a little known fact, cooked whole food (meats, veggies and fruits) is also highly digestible and produces low odor, small volume stool. Studies are also showing that cooked whole food is more digestible and allows for better nutrient absorption and less risk of pathogen issues, but, again, another discussion.
Lest you think I’m anti kibble, we feed kibble and supplement with whole, healthy foods and we see very low odor and low volume. So healthy stool from commercial food is possible, but not as common, because kibble quality is often not optimal and because we do not teach and encourage divers microbiomes in our dogs via a varied diet.
Many vets and experienced breeders will be able to tell you if a dog has parasites just by the stool odor (this should, of course, be confirmed by a fecal, when possible, but it’s also important to remember that not all parasites can be seen in a fecal).
A less-known cause is food quality. Low digestibility causes more food to remain in the digestive tract which provides more food for gut bacterial to feed on. Additionally, the types of food matter that are less digestible are often most fed on by less desirable gut bacteria. A by-product of these less desirable gut bacteria includes hydrogen sulfide, which is main stinkifier of poop (how’s that for a technical term?)
Other poop stinkifying chemicals are methyl sulfides (from brassica plants, like broccoli and cabbages), indoles (produced by some gut bacteria), and skatoles (a result of the breakdown of tryptophan. Another weird but interesting poop fact: indoles and skatoles are also present in flower scents. So, I suppose it could be argued that, yes, poop does smell like roses!
Other causes of stool odor includes a high fat content of food, GI diseases, pancreatitis, food intolerances, viral or bacterial infections, medications and supplements, and many other reasons.
Remember, poop is food that can’t be digested. So poop volume, while not the only indicator of digestibility, is an easy indicator of digestibility we can see and evaluate daily.
Consistency of all the above poop factors
When looking at poop health, you also want to note that poop characteristics remain similar from day to day. While poop and poop habits can vary by individual, when there’s a drastic change in poop or poop-associated behaviors and you can’t identify a good reason, you may want to consider the presence of a problem.
Here's to healthy pooping!
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References & notes
Human saliva has enzymes (amylases) that starts the digestion of starches, but dogs don’t have amylases in their saliva. Amylases, however, are present in the canine pancreas. Wolves also have amylases but in much smaller amounts as dogs evolved alongside humans as scavengers and evolved to have more copies of digestive amylase genes (about 28 times more than wolves), per Animal Genetics, Volume 45, Issue 5, Article first published online: 28 Jun 2014. https://onlinelibrary.wiley.com/doi/pdf/10.1111/age.12179
“Diseases of Eyes, Claws, Anal Sacs, and Ear Canals” in Small Animal Dermatology, 4thEd., 2017, pages 413-447
 Axelsson, E., Ratnakumar, A., Arendt, M. et al. The genomic signature of dog domestication reveals adaptation to a starch-rich diet. Nature 495, 360–364 (2013) doi:10.1038/nature11837
 Botigué, L., Song, S., Scheu, A. et al. Ancient European dog genomes reveal continuity since the Early Neolithic. Nat Commun 8, 16082 (2017) doi:10.1038/ncomms16082
 Frantz, LA, et al. "Genomic and archaeological evidence suggest a dual origin of domestic dogs." Science 03 Jun 2017: 1228-1231