Wolves, Dogs, Differ in Ability to Digest Starches

Study finds genetic differences between dogs and wolves, with dietary implications.


Domestication appears to have led to genetic changes in dogs that make them able to digest starches better than wolves can, according to a paper published in Nature in January.

Kerstin Lindblad-Toh, a geneticist at Uppsala University in Sweden, led the team that looked for genetic differences between the genomes of 12 wolves from around the world and 60 dogs from 14 different breeds. They found 36 areas in the genome where dogs differed from wolves, but not from dogs of other breeds, indicating changes likely linked to domestication. Nineteen of the regions found involve the brain, and 8 of those are involved with nervous system development that could help to explain behavioral changes that make dogs friendlier, less fearful, and less aggressive toward humans.

Another 10 genes were found to help dogs digest starches and break down fats. The researchers believe that 3 genes in particular make dogs better at splitting starches into sugars and then absorbing them in the gut. Interestingly, most humans have also evolved the ability to more easily digest starches in what appears to be a case of parallel evolution. The researchers suggest that the adaptations in both species are likely linked to the development of agriculture about 10,000 years ago.

These new findings help to support the theory that dogs may have become domesticated by hanging around human settlements and scavenging their scraps and waste. The study does not rule out the possibility of earlier domestication, however, which is supported by fossil records that may go back 33,000 years, or of later interbreeding with wolves. Another scientist plans to analyze fossil DNA to try to discover when these changes first appeared. Changes in digestion may have developed after behavioral changes that could have occurred much earlier, when our human ancestors were still hunter-gatherers.

What does it mean?
In 1997, I attended a seminar at Wolf Park in Indiana, where I learned that wolves cannot digest starches very well and require a high-meat diet in order to thrive. The wolves at Wolf Park are fed primarily deer carcasses, but when those are in short supply, the wolves are given Nebraska Brand carnivore diets that are mostly meat with very little carbohydrate content, rather than dog food.

In contrast, most dogs digest starches well, as evidenced by their ability to utilize the calories and nutrients provided by dog food that is high in carbohydrates. Already, some people are claiming this study supports feeding high-carbohydrate diets to dogs, but I disagree. The study says, “Our results indicate that novel adaptations allowing the early ancestors of modern dogs to thrive on a diet rich in starch, relative to the carnivorous diet of wolves [emphasis is mine], constituted a crucial step in the early domestication of dogs.”

Since wolves consume almost no starch, a diet that is relatively rich in starch does not mean that grains and other starchy foods would (or should) make up the majority of the diet. It also does not mean that dogs require starches in their diet, and it does nothing to support feeding a highly processed diet rather than fresh foods. The parallel evolution involving starch digestion in humans and dogs could also help to explain similarities in certain diseases, including diabetes and inflammatory bowel disease, indicating that there could be drawbacks as well as advantages to eating diets that are high in starch.

The flip side is that I do think this study supports the idea that it’s acceptable to include some starch in your dog’s diet, as long as it doesn’t cause problems for an individual dog. For example, I feed my own dog a homemade diet that is high in protein, but I also include carbohydrates in the form of vegetables, fruits, and even grains (she gets a meal of cereal, yogurt, and banana for breakfast every fourth day).

I don’t believe it’s necessary or even advisable to avoid starches altogether unless you have an individual dog who reacts badly to them, and even then, she may do well with some starches, even if she has problems with others. Whole grains are high in some vitamins and minerals and provide fiber (prebiotics) that helps to support beneficial bacteria in the intestines (probiotics). Other starchy foods, such as potatoes, sweet potatoes, and bananas, also provide nutrients that may otherwise be lacking in a homemade diet.

The study also found a variation between dogs in the number of duplicate genes involved in the production of amylase, a pancreatic enzyme required for the first step of starch digestion. While wolves had 2 copies of this gene, called AMY2B (one of the three genes identified above), researchers found a range of 4 to 30 copies in the dogs they studied, indicating that some dogs (and possibly some dog breeds) are better at digesting starches than others.

As always, it’s important to do what works for your dog. If she has digestive issues when consuming a diet that is high in starch, or shows signs of inflammation, such as from allergies or arthritis, it’s worth trying a low-starch diet or even eliminating starchy foods completely to see if improvement is noted. – Mary Straus

For More Information:
“The genomic signature of dog domestication reveals adaptation to a starch-rich diet,” Nature, published online 1/23/2013
Wolf Park, Battle Ground, IN. (765) 567-2265; http://wolfpark.org

Antifreeze Becomes Safer (Finally)
Manufacturers agree to add bittering agent to deter pets from ingesting antifreeze.

On December 13, 2012, the Consumer Specialty Products Association (CSPA) and the Humane Society Legislative Fund jointly announced that all major marketers have agreed to voluntarily add a bitter flavoring agent to all antifreeze and engine coolant products manufactured for sale in the United States to deter animals and children from ingesting them. This is great news about a change that will save many lives.

Each year, up to 90,000 pets are poisoned by ingesting antifreeze that drips onto our garage floors and driveways, or is left in open containers. Antifreeze has a sweet taste that makes it attractive to pets, livestock, wildlife, and small children. As little as one teaspoon of antifreeze can kill the average cat. The minimum lethal dose in dogs is about 2 ml (less than half a teaspoon) per pound of body weight.

Most antifreeze products are 95 percent ethylene glycol, a potent alcohol that is readily absorbed once it is ingested. Its effects start with alcohol toxicity to the central nervous system, beginning as soon as 30 minutes after ingestion and lasting up to 12 hours. Signs may include ataxia (loss of balance), disorientation, and appearing “drunk.” You may also notice increased drinking and urination. The pet may seem to recover within a few hours, only to get worse again with possible coma or seizures. If the pet survives, the next stage involves cardiopulmonary effects due to severe acidosis and electrolyte disturbances. These generally occur 12 to 24 hours after ingestion and may include rapid breathing and heart rate, depression, seizures, and/or pulmonary edema. Within 24 to 72 hours, the pet goes into kidney failure due to damage caused by calcium oxalate crystals from the breakdown of ethylene glycol in the body. Early veterinary care is essential to survival; failure to properly treat within the first several hours may lead to irreversible damage or death.

Some newer antifreeze products use 50 percent or more propylene glycol in place of ethylene glycol, making them safer than older products, but propylene glycol can still cause alcohol poisoning. Doses of more than 10 ml/kg (about 1 teaspoon per pound of body weight) are considered potentially toxic to dogs.

Seventeen states have passed legislation requiring antifreeze manufacturers to add a bittering agent to their products that makes them unpalatable to animals and children. Federal legislation had been introduced but did not progress. Denatonium benzoate, the bittering agent used, is a common ingredient in many household products and has been used in anti-nail biting formulas for decades.

Although the change takes place immediately, older products already on shelves and in cars will still be around for awhile, so continue to exercise caution regarding the products you use in your own vehicles, and to minimize exposure your pets may have to these substances. – Mary Straus

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Mary Straus has been a regular contributor to Whole Dog Journal since 2006. Mary first became interested in dog training and behavior in the 1980s. In 1997, Mary attended a seminar on wolf behavior at Wolf Park in Indiana. There, she was introduced to clicker training for the first time, and began to consider the question of how we feed our dogs after watching the wolves eat whole deer carcasses. Mary maintains and operates her own site, DogAware.com, which offers information and research on canine nutrition and health. DogAware.com has been created to help make people more "aware" of how to make the best decisions for their dogs. It's designed for people who like to ask questions and understand the reasoning behind decisions, rather than just being told what to do.  Mary has spent years doing research for people whose dogs have health problems, or who just want to learn how to feed them a better diet. Over this time, she has learned a great deal about dog nutrition and health, including the role of diet, supplements and nutraceuticals.  In 2007, she was asked by The Ivy Group to contribute to The Healthy Dog Cookbook. She previously also wrote a column for Dog World.