Like humans, dogs digest their food at individualized rates. However, it is possible to estimate how quickly dogs digest food based on the size, breed, and age of the dog as well as the type of food that was eaten and how much exercise the dog gets.
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Dog vs. human digestion
Don't bother estimating how long it takes your dog to digest food based on how long it takes you to digest your food. While humans take about 36 hours to fully digest a meal, dogs digest their meals in four to eight hours, although for some dogs, 10 to 12 hours is the norm. Size is one reason. Humans are typically much larger than dogs and have much longer intestines for food to pass through.
Size of the dog
Whether a dog is large or small makes a difference in how long it takes him to digest his food. Large dogs typically take about eight hours to digest a meal, though it is normal for individual dogs to take as long as 10 to 12 hours. Small dogs, including toys, minis, puppies, and others that are considered small, digest food in about half the time as large dogs: around four hours. This is primarily because the food has so much less space that it has to travel in a small dog than in a large dog.
Breed of the dog
A dog's breed affects how long it takes to digest food, partly because breed determines size. For example, great Danes are notably very large with intestines that are far larger than those of a toy poodle. So, it's not surprising for great Danes to take twice as long to digest their food – about eight hours compared to four hours for a toy poodle.
Breed also contributes to a dog's overall health and certain health issues. Some breeds are prone to osteoarthritis, for example, which can make it painful to pass a stool and can result in constipation. A dog's natural urge to chew is more pronounced in some breeds, like Jack Russell terriers, Labs, German shepherds and others, so they may chew an object into pieces and swallow them, which tends to take longer to digest than food.
Call your vet if you think your dog ate a nonfood item, especially if it is taking an excessively long time to digest. It may have caused a dangerous obstruction that requires quick medical attention.
Age of the dog
Dog metabolism slows down as they age, and that affects digestion too. So, senior dogs often take longer to digest their food than when they were younger. How much longer depends on many factors, including the dog's overall health, energy and activity level, and digestive issues that can cause constipation, a condition that is also more common as dogs age. A dog's metabolism typically changes gradually over time. Owners should know what is normal for their dog and when to be concerned.
Type of food eaten
How quickly dogs digest their food also depends on what was in the food they recently ate. Foods high in fiber help to pass food through the digestive system more quickly, so if your dog is experiencing constipation more often, perhaps due to aging, try adding more fiber to the diet slowly, as adding too much too quickly can cause diarrhea.
Add some fresh fruits or vegetables, like pumpkin or green beans, which are both high-fiber foods that most dogs like. Be sure not to give dogs food that is toxic to them or that is cooked with toxic ingredients, like onion or garlic.
Exercise and activity level
Exercise helps keep digestion at a normal rate because when dogs expend energy, the body sends the food stored in their stomach through the intestines to become caloric energy. This could partially explain why senior dogs may take longer to digest their food and even why they become constipated more easily since they don't exercise as much as they once did. Health issues often increase with age, and they may make it harder to keep exercising, especially those that affect movement, including arthritis, problems with hips and knees, and spinal conditions.