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The following information; (dry matter basis, biological value, net utilization, etc) is adapted from an old "Max's House" website's thorough discussion of Cats nutritional needs and how [ wet ] and [ dry ] commercial cat foods meet those needs; and (CRF, chronic renal failure) low protein/low salt/low phosphorus diets for cats with kidney problems from the Feline CRF Information Center website ; and ( FLUTD, urine acidity, etc) from "Feline Urinary Infections" by Laura Pasten, D.V.M. . Calculate your cat food's Dry Matter Basis (DMB) protein and water content on PurrInn Cats Hostelry's H20 + DMB Calculator Excel spread sheet.

The cat has evolved to obtain sufficient water almost entirely from moisture present in food. The nonfat component of mammals (cats natural prey) contains about 73% water. Cats can live for long periods without drinking water when eating food containing 67-73% water but often become dehydrated when the water content of the food is 63% or less. A cat consuming a 240 kcal dry diet containing 8% moisture must consume 96% of its total water intake by drinking, needing to drink over 7 oz. of additional water per day.

Cats increase voluntary water intake when fed dry food but usually not in sufficient amounts to fully compensate for the lower moisture content of the food. The first indication of insufficient water intake is often small dry feces. A healthy cat's feces should be formed but soft. If the litter does not stick to the feces, your cat may not be adequately hydrated. Cats can often be encouraged to consume sufficient water by adding a small amount of dry food to their water dish, serving their dry food in warm water, or adding a small amount of warm water to any wet/canned food they receive.

All animals have a metabolic requirement for glucose. However, an absence of plant carbohydrate in the feline diet will not affect blood glucose levels or cause an energy deficiency; because the cat’s body uses protein and the glycerol portion of fat for glucose production, and primarily fat and protein for energy, while storing most of the excess carbohydrate in the body as glycogen and fat. Cats can receive all their energy and nutritional needs from protein and fat. Further, if a cat’s diet includes excess carbohydrates, much of what the cat eats is only partially digested by the time it reaches the large intestine, overloading the digestive and excretory systems. Commercial dry cat foods often contain as much as 45% - 50% carbohydrates. Although much of the plant-based carbohydrates commonly found in cat foods may have high biological value for herbivores or omnivores, those carbohydrates have much less value for a carnivore such as the cat.

On a “dry matter basis" (DMB) {% protein divided by Total Dry Matter (TDM = 100% minus the percentage of moisture on the label)} dry foods are about 38% protein, while canned foods are about 40% protein. In general, the more meat or animal protein your cat eats, the more acidic his or her urine will be.  The more grain or carbohydrates your cat eats, the more alkaline his urine will be (although this varies cat-to-cat). Cats with a low urinary pH (more acidic) have very few urinary infections; cats with a higher urinary pH (more alkaline) have more frequent urinary problems. In addition, while Veterinarians often prescribe a low protein/low salt/low phosphorus diet for cats with Chronic Renal Failure (kidney problems) to reduce the amount of waste materials in the system that must be filtered out by the kidneys, some experts believe that high quality protein that produces little waste may be preferable to simply reducing overall protein, and that any benefit from eating low protein food may be from the lower content of phosphorous contained in the food rather than the low protein itself.

In a recent survey, the protein content's biological value was given as 60% for the leading dry food and 70% for a well-known canned food. Animal protein is generally more expensive and often of higher quality than plant protein. The composition of canned foods allows the use of protein and fat sources of higher biological value than can be used in dry food. Pet food's protein digestibility is about 80% for dry, 85% for semi-moist and canned foods containing large amounts of cereal grains, and 90% for canned diets with meat as the primary protein source.

Net utilization, the amount of food that can be used by the cat in relation to the amount provided, equals digestibility times biological value, or about 59.5% for semi-moist and canned foods with large amounts of cereal grains, 63% for high quality canned foods with meat as the primary protein source, and 48% for dry foods which contain more plant protein and carbohydrates.

Minimum protein requirements of cats are 30 and 26 percent of calories for growth and maintenance, respectively. Thus 26% - 40% (DMB) of the daily kcal derived from protein, depending on the quality of the protein, should meet the needs of nearly all adult cats at maintenance. Fat calories should account for between 20 and 40 percent (DMB) of total caloric intake. The apparent digestibility of the fat content of cat food is 96 percent for canned foods, 92 percent for semi moist foods, and 79 percent for dry foods.

When choosing a cat food it may be important to consider not only adequate percentages of high quality animal protein, water, and fat, but also limiting excess percentages of carbohydrates or plant products, as indicated by both the analysis and the major ingredients, to arrive at an acceptable nutrition/cost decision. Keep in mind that a food with several kinds of plant/grains listed lower on the label may have as much total plant/grains as a product that has one or two listed high on the label

Follow dietary recommendations from a knowledgeable veterinarian to prevent nutrition-induced disease in your cat.