Formulating a diet for cats requires that sufficient nutrients and energy be available to supply the needs of the animal depending on whether the needs are for growth, maintenance, pregnancy or lactation. The diet must be looked at in terms of its biologic value. This is determined by the edibility, digestibility and metabolizability of the diet.
If a cat consumes all the diet, the food is considered one hundred percent edible. Digestibility is determined by measuring the amount of the nutrient — for example, protein eaten minus the amount of protein recovered in the feces. Metabolizable energy is the gross energy of the nutrient minus the energy of the feces and urine. From these measurements the biologic value is determined.
Table 1: Minimum Requirements for Growing Kittens (units per kg of diet, dry basis)*
|Methionine plus cysteine||g||7.5|
|Phenylalanine plus tyrosine||g||8.5|
|Vitamin A (retinol)||mg||1|
|Vitamin D (Cholecalciferol)||µg||12.5|
|Vitamin E (- tocopherol)||mg||30|
|Vitamin K (phylloquinone)||µg||100|
|Vitamin B6 (pyridoxine)||mg||4|
|Folacin (folic acid)||µg||800|
|Vitamin B12 (cyanocobalamin)||µg||20|
*Table composed by the National Research Council
The nutrient requirements of the National Research Council are listed in Table 1. These requirements are for purified feline diets that have a very high bioavailability. The bioavailability of natural ingredients used in cat foods will vary from the purified diet.
In general, protein digestibility and amino acid bioavailability of ingredients used in cat foods will not exceed 90%. If there is a high amount of collagen in the food, digestibility may only be 50%.
The National Research Council hopes to correct for these differences in bioavailability by suggesting that their minimum values for concentration of amino acids be multiplied by a factor 1.3. They recommend that their minimum requirements for the B-vitamins in the table be multiplied by 1.6 to help extrapolate the figures in the table to practical diets. Thiamine requires additional precautions due to loss during cooking and processing.
Just as important as the biological value of a diet are the different requirements of each stage of the life cycle, mainly growth, maintenance, reproduction and lactation. The NRC in its table has given the minimum requirements for growing kittens. Due to the fact that research into the area of feline nutrition has only begun to increase in recent years, knowledge in this area is still limited.
The NRC has not set minimum requirements of nutrients for maintenance and reproduction. They believe that the minimum requirements listed for kittens are adequate for other stages if certain changes are made. For maintenance the levels of protein and methionine should be reduced as noted in the table and for reproduction vitamin A and taurine levels should be increased.
Energy requirements differ during the various stages of a cat’s life. Miller and Allison recommend the following energy requirements for growing kittens and active adult cats:
- 250 kcal / kg body weight at 5 weeks of age.
- 100 kcal / kg body weight at 30 weeks of age.
- 85 kcal / kg body weight at 50 weeks of age.
An inactive, confined cat may need only 70 kcal / kg body weight of energy per day. Energy requirements increase during gestation, such that most researchers believe that unspayed cats require about 25% more energy, particularly in the later stages of pregnancy.
It is not uncommon for female cats to lose weight during lactation, even though they have free access to a very palatable diet. In one study of ten lactating cats in the first six weeks postpartum energy requirements increased from 90 to 270 kcal metabolizable energy / kg maternal body weight.
The feeding behavior of the cat is also quite characteristic. Cats usually prefer to eat alone without competition from other cats or pets. It is suggested that if two cats are in a household, feed each in separate bowls which are placed at different areas of the room. If a dog is in the household, it may be best to place the cat’s bowl in some elevated location that the dog can not reach.
The cat is an adaptable and opportunistic feeder, which was required in its evolution from a wild carnivore. In the wild it had to stalk and capture its food, so meals depended on the type of wildlife in the area. If wildlife caught was rather large in size, it would mean that meals would be large and probably infrequent.
If the area supplied an abundance of mice, the cat would probably adapt to having small meals frequently throughout the day. Domestic cats on a free-feeding method were usually found to nibble randomly throughout the day. Some would eat 10 – 20 small meals in a 24 hour period.
Most researchers agree that cats can regulate their caloric intake quite well, no matter what type of food is available. Most cats will voluntarily restrict their energy intake to that energy which is needed by the body.
One study found that cats fed varying diets were able to adjust their intake after a very short time, so that mean intake at each meal remained constant. This occurred even when some meals were of low caloric density and required a bulky intake to satisfy caloric needs.
If needed, a cat can easily meet its energy needs on one large meal per day. It is important that meals be of good quality but not overly palatable.
Selection of a well-balanced commercial cat food is not as easy as it may seem. There are two main methods by which food is judged to be nutritionally adequate. The manufacturer may claim on the label that the food meets the standard requirements set by the NRC. This is one way in which the nutritional value of the diet can be assessed.
But statements of the nutrient value of a diet tell nothing about the diet’s palatability, bioavailability or protein quality. Feeding trials, which are a second method of judging the quality of a diet, are better indicators than NRC requirements. If a food is labeled “complete, perfect, a scientific or balanced ration for cats”, it must meet the NRC requirements or have been proven in feed trials.
Reading the nutritional statement on the label can be quite helpful. Also note the label for guarantees and analyses. There should be a guaranteed minimum percentage of protein and fat and guaranteed maximum percentage for fiber and water. These are minimums and maximums and do not necessarily indicate the quantity of these substances in the food.
Economically it may not be recommended buying a canned food with greater than 75% moisture. If a canned food has less than 5% fat or if a dry food has less than 7% fat, the caloric density may be considered too low. The list of ingredients on the food gives a general idea of what is in the food and whether vitamin and mineral supplements have been added.
It is recommended that a good quality food be purchased, rather than supplementing a poor quality diet. Cats frequently develop a preference for one type diet over another. These preferences develop as a result of previous dietary experiences and are not due to a requirement for certain nutrients.
Commercial cat foods come in a variety of forms. There are canned ration, canned gourmet, semimoist and dry types of foods available. The digestibility of canned food is usually higher than that of dry foods.
Canned foods have from 72% – 78% moisture. The canned ration type foods are many times labeled as nutritionally complete and they supply energy from protein, fat and carbohydrates in fairly substantial quantities.
The gourmet canned foods are designed to add variety to the diet but not formulated to act as a sale source of nutrients. They are frequently nutritionally incomplete and energy is supplied mostly through protein and fat. Gourmet canned foods are usually the most expensive type food and are highly palatable, such that cats seem to become addicted to one certain variety.
Semimoist cat foods are intermediate in moisture between the canned and dry foods. They contain less fat than canned foods and generally have more cereal than canned foods, so that more energy is supplied by carbohydrate and less by fat.
Semimoist foods have products added to stabilize the product, maintain water levels and prevent spoilage, as refrigeration is not required. Such things as sugar, sodium chloride, sorbates and propylene glycol may be added.
To control bacterial growth, pH is maintained using phosphoric acid. Use of phosphoric acid may increase phosphorus levels in the food enough to lead to problems in cats susceptible to feline urologic syndrome.
Dry foods are composed of 7% – 12% moisture and are mainly carbohydrate and protein with very low fat content. Dry foods have substantial quantities of cereal grains, milling byproducts and soybeans added with poultry byproducts, fish meal, “digest” and animal fat present to increase palatabilty. Crude protein is 28% – 36%, on a dry matter basis, less than that in most canned foods, but very similar to the content in the semimoist foods.
Dry foods have the advantages of costing less, offering a wide variety of protein sources therefore, decreasing chances of cats becoming addicted and being easy to store and feed. Some nutrients may be destroyed in processing and later in post-processing oxidation.
“Digest” is frequently being used in dry cat foods. This is a liquid which is sprayed on the exterior of dry cat food to increase palatability by providing flavor and acidity.
Cats seem to prefer acid over neutral or alkaline foods. “Digest” is made by enzymatic breakdown of a variety of animal products, such as poultry byproducts, liver, fish and beef lungs. The action of the enzyme is then stopped by adding an acid. Eventually the acid provided by the digest must be excreted by the kidney.
It can be seen that each of the commercial cat foods has its advantages and disadvantages. Some owners choose to feed their cat a homemade type diet. This, even though well-intentioned, is not recommended as frequently the cat is fed one predominant food which leads to an imbalanced diet.
One course recommends choosing a canned ration type food of a manufacturer, which is labeled to provide complete and balanced nutrition. Otherwise, it is suggested that a mixture of two or more types of foods be fed to provide the necessary nutrients. So, for example, feed one-half the energy requirement as a canned food and provide the remaining energy as a dry food.
Also, during periods when extra energy is needed, such as growth, pregnancy and lactation, it may be wise to provide a diet which is more energy dense. One study compared a dry cat food with 21% fat to a leading kitten diet with 12% fat. The diet with the higher fat content resulted in 10% higher birth weights, 40% greater kitten survival and a 30% greater weight gain in kittens from birth to weaning.
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