Why Large Breed Dogs Have Poorer Food Digestion

By Ken Tudor, DVM on Jun. 23, 2015

Why Large Breed Dogs Have Poorer Food Digestion

I have noticed in my 32 years of veterinary practice that large breed dogs, especially German Shepherds, have larger and more frequent watery stools and digestive problems with commercial dog food. Owners and their veterinarians often observe the same problem. As it turns out there are anatomical and physiological reasons for this: The digestive tract of large dogs functions differently than smaller dogs, creating this problem.

Veterinary researchers from France presented their findings during a lecture I attended at the American College of Veterinary Internal Medicine Symposium in Indianapolis, Indiana recently.

What are These Digestive Differences?

The weight of the intestines in large dogs is only 3 percent of their body weight compared to 7 percent in smaller breeds. This means there is less intestinal area for digestion and absorption of the nutrients in the diet.

The time that food spends in the colon is longer for large breed dogs. That means that the colon bacteria have longer to ferment food products. This increases by-products that promote more water in the colon, causing more watery, frequent stools.

What Are the Solutions to These Digestive Differences?

More non-fermentable fiber in the diet. The guaranteed analysis on the label of dog food lists the total crude fiber, which really is not an indication of the fiber in the diet. Fiber can be divided into two major types. The first is indigestible or digestible fiber. As their names imply, indigestible fiber adds bulk to the diet and stool and passes with the stool. Digestible fiber can be used by the cells of the colon lining and are divided into two classes, fermentable fiber and non-fermentable fiber.

Bacteria in the colon use fermentable fiber as food to produce fats and lactic acid, which causes the intestinal contents to react like a sponge and draw water into the colon. By decreasing the amount of fermentable fiber in the diet, there is less water in the colon and large dogs have a more firm, formed stool.

Unfortunately, less fermentable fiber in the diet of smaller breed dogs causes constipation and a harder stool because of the anatomical intestinal differences.

Increased protein digestibility. Large breed dogs experience poorer stool quality with less digestible protein. This, I think, is an important point, but because the researchers worked for Purina they only compared wheat gluten protein to chicken meal protein. They found improvements in stool quality with the higher digestible wheat gluten, but the water content of the stool for both groups was quite high. I think this is why owners of large breed dogs have varied responses with commercial dog food. Their dogs have a variable response to wheat gluten or chicken meal.

Large dogs on homemade diets with highly digestible meat proteins tend to have much better stool quality.

Resistant, gelatinized starch improves stool quality in large dogs. The researchers found that the starches in foods that were less fermentable and more highly processed had better stool quality. In order to increase the gelatinization of starch it has to be exposed to extreme increases in temperature during processing. What these researchers found is that if you cook the hell out of the starch in the food, larger breed dogs will make better stool. But the higher temperature also causes more destruction of the nutrients in the food. The stool is more firm but the dog may be malnourished.