I have two different answers to the question in the title followed by some confusion and I am surprised. From the respected book Wild Cats of the World, I have the information that for a domestic cat to remain healthy its diet must contain 12% protein by weight for adult cats and 18% the kittens.
From another respected book on medical care for your cat, Cat Owner’s Home Veterinary Handbook, I have the following information which is that the ideal natural cat diet for domestic cats, the mouse, is 40% protein, 50% fat and only 3% carbohydrates.
I suspect that the former tells us the minimum protein requirement while the latter tells us the classic protein-based diet for the domestic cat whose body is a reflection of its diet.
In fact, the veterinarians go on to say that the diet of an adult cat must be at least 26% protein. This does differ from information provided by the Sunquists who wrote the Wild Cats of the World.
By comparison, dogs can survive on much less protein. They can get along with only 4% protein. Dogs can thrive on a vegetarian diet but it is difficult to create a vegetarian diet for a domestic cat. There is a discussion about vegetarian o vegan diets for cats. It’s possible to do it provided the manufacture ensures that the right nutrients are added.
The building blocks of protein are amino acids. A cat’s diet must contain more than 20 amino acids to be complete. There are 11 essential amino acid requirements: histidine, isoleucine, arginine, methionine, phenylalanine, threonine, tryptophan, valine, leucine, lysine and taurine. Cats cannot convert amino acids to taurine. It has to be in their diet because without it cats develop retinal changes leading to blindness. It also causes a serious heart condition cardiomyopathy. It’s contained in certain seafoods and also in organ meats. Cat foods should contain at least 0.02% taurine on a dry matter basis.
Without arginine cats show neurological signs because of high level of ammonia in their blood.
The amino acids methionine and cysteine are converted to glucose to be used to provide energy. Cysteine is also important hair growth and it provides felinine which is important for scent marking when excreted in urine.
Many cats can manufacture enough tyrosine while others need to get it from their diet. It’s important in the production of melanin (a pigment). When there is a shortage of tyrosine you might see a black cat turning reddish-brown.
Carnitine is an amino acid which is synthesized in a cat’s kidneys and is important for weight loss and cats, and in the treatment of hepatic lipidosis.
In America cat owners shouldn’t need to worry about the above information because an important indicator of the quality of cat food is a statement on the label which says that the diet meets the standards set by the Association of American Feed Control Officials (AAFCO – but see below). The label should describe the product as “complete and balanced”. If it doesn’t say this you can assume that it is not a complete diet. If it does said it, it should have the requisite protein levels commensurate with your cat’s requirements.
As for kittens, if the food has been formulated to support kitten growth the product should be labelled as such and the claim must conform to one of the AAFCO profiles that stage of life.
There’s an interesting article on the petmd.com website in which they say that the minimum protein levels specified by the AAFCO may be too low. What appears on the label of cat food is the minimum protein percentages which is an AAFCO number. According to this organisation the figure is 26% for adult maintenance and 30% for kittens.
Research indicates that the minimum daily protein requirement for adult cats appears to be at least 5.2 g per kilogram bodyweight which is “well in excess of the current AAFCO recommendations”.
The problem appears to be in how to work out the protein requirements. There appear to be two methods one is based upon lean body mass and the other is based upon nitrogen balance.
It is difficult to draw a precise conclusion because a precise number for the required percentage of protein in cat food is hard to pin down. The petmd.com website author, Jennifer Coates, recommends that cat owners look for dry food with at least 30% protein and supplement it with a 40-50% protein can food.