Is it ok to feed my cat dog food?

If you have both dogs and cats in your house, you may occasionally catch your feline friend snacking out of the dog bowl. Some people may even wonder why they need to buy separate foods for their cats and dogs since they seem to want to share. All those dry kibbles look the same and all those meaty moist chunks look pretty similar, too. Are they really so different?

As we are fond of saying in feline medicine, "cats are not small dogs", and there are some significant differences between the two species when it comes to digestion. 

1) Food moves through a cat's digestive tract more quickly than a dog's, both because it is shorter, and because it is speedier.

2) A dog's caecum is more developed than a cat's, allowing more breakdown of plant material

3) The intestinal lining is different

4) Dogs have some plant-crushing molars while cats do not have any teeth suited to grinding plant material

5) Cats require more dietary protein than dogs (a minimum of 8% more, by AAFCO standards)

6) Cats cannot make the amino acid taurine from their diets like dogs and people can

7) Cats cannot make nicotinic acid from tryptophan well

8) Cats cannot turn beta carotene to retinol, so need dietary vitamin A supplementation

9) Cats cannot make linoleic acid from arachadonic acid well, but they need both fatty acids in their diets

10) Cats cannot cope with high levels of carbohydrates

Everything that a cat cannot make in large enough amounts to fulfill their dietary needs must be supplemented in their diet. Dogs, in contrast, can make these nutrients from the food they eat, so dog food does not contain extra supplements of taurine and vitamin A, sufficient levels of protein, etc.

What happens when a cat is fed a diet lacking in these nutrients?

A lack of vitamin A can cause changes to the retina, development of cataracts and other eye issues, muscle weakness, and weight loss or poor appetite.

Nicotinic acid is related to vitamin B3, and a lack of this nutrient causes weight loss, weakness, poor appetite and diarrhea. Cats also have different thiamin and folic acid requirements than cats.

Fatty acids are essential for skin and coat health, immune function, and control of inflammation. Arachidonic acid also is involved in the health of the kidney.

Most importantly, however, a lack of taurine in the diet can cause irreversible damage to the heart retina of the eye (central retinal degeneration). Taurine is an amino acid that is found in muscle meat. It is found all over the body, but is concentrated in the brain, eye and heart muscle. It helps with digestion and absorption of fats and fat soluble vitamins, the formation of bile salts, and is involved in eye health, brain and nervous system function, heart function, immune function and female reproduction and fetal growth.

It can take as few as 10 weeks for the cone photoreceptors of the retina begin to deteriorate when a vision are handled by the cone receptors of the eye, while low-light vision is the responsibility of the rod receptors in the retina. After 20 weeks of low-taurine diet, many of the cone receptors will be completely unresponsive, and eventually the rod photoreceptors will also be affected. A very classic and unique lesion will form equally in both eyes, and if left untreated, blindness is the end result.

cat's diet is low in taurine. Color and daylight

Besides these eye issues, taurine deficiency can cause dilated cardiomyopathy. Before it was understood that cats had a special need for supplemental taurine in their diets, the leading cause of dilated cardiomyopathy in cats was taurine deficiency. In 1987, the connection was made between the heart disease and the low level of taurine in many diet, and cat food standards were corrected. Now, DCM is rare. The wall of the heart, the myocardium, contains the highest concentration of taurine anywhere in the body of the cat. With a deficiency, the heart muscle weakens. It cannot contract as well as it needs to to pump blood, so blood pools in the chamber and the ventricle swells. This can lead to the formation of a large blood clot, or can lead to congestive heart failure. If caught early, the damage to the heart can potentially be reversed, but the changes to the retina are permanent.

 Taurine deficiency can also cause a decrease in blood proteins and white blood cell numbers, which can affect immune function.

Most cats that develop a taurine deficiency do so because they are eating a low-quality diet, dog food, or a home cooked meal that is poorly balanced (even if you feed muscle meat, cooking can degrade or destroy taurine, so it may still need to be supplemented). Preventing taurine deficiency is achieved by feeding a higher quality diet. However, in some cases, a cat may develop a deficiency even when fed a high quality diet, and in these cases, taurine supplementation beyond a normal diet is necessary.

Because of these special nutritional needs of cats, it is not a good idea to feed your cat a diet of dog food alone. If your cat occasionally snacks from the dog bowl, you shouldn't be too concerned, but your cat should have plenty of nutritious cat food readily available.