To understand the cat's complex and highly individual pattern of feeding it is important to consider its ancestry. The domestic cat (Felis catus ) is adapted to a hunting lifestyle existing on an almost totally animal diet. Its jaws, digestive system and behaviour have been developed to accommodate this behaviour. Throughout the process of domestication the cat has not changed significantly in its nutritional and behavioural needs and it has remained dependent on animal tissues as the main source of its food. The sensory system of cats is particularly adapted to respond to the constituents and sensory qualities of meat.
Because it is an obligate carnivore and therefore has special dietary requirements which distinguish it from other carnivores such as the dog, the cat requires animal derived tissue in its diet and has a higher protein requirement than many other mammals. Cats are unable to adjust to a low protein diet and will use body protein to satisfy their needs. The uniqueness of this species has been demonstrated by their specific dietary requirements. A deficiency of the amino acid, arginine, in a single meal can lead to clinical signs of lethargy, hypersalivation and vocalisation. Arginine is required by the cat to synthesise urea, a waste product resulting from the breakdown of protein.
Another essential nutrient for the cat is the amino acid, taurine, which the cat cannot synthesise sufficiently to meet its needs. The cat's diet must therefore contain taurine in sufficient quantities. If a deficiency develops there is a high risk of serious and irreversible damage to major organs such as the eye and the heart. Taurine is found almost entirely in meat and supports the concept of the cat as an obligate carnivore.
Whilst it is difficult to establish a direct relationship between nutrition and longevity, it is obvious that inadequate or deficient diets do have a major impact on critical stages of the life cycle of the cat, such as, reproduction, the rearing of a healthy litter, growth and development. It is also obvious from the above that certain illnesses have a dietary component to their onset and can have serious consequences for the cat.
Perception of flavour
The factors that can influence a cat's perception of 'flavours' include a food's odour, taste, texture and temperature.
The olfactory apparatus (organ of smell) of domestic cats is far more sensitive than that of humans. The perceived odour from food is particularly important for the initiation of feeding. If the odour is highly palatable to the cat then that alone will encourage consumption of an otherwise bland diet. However, the response to odour will be less if the cat does not taste the food too. The sense of taste combined with the sense of odour are most important in the perception of flavour. Cats have taste buds on their tongues that respond well to substances classified by humans as salty, sour or bitter. Unlike many mammals, cats do not appear to respond to the taste of 'sweet', but their taste buds are particularly sensitive to the constituents of meat - thus cats respond to various amino acids, the building blocks of animal proteins.
The texture of a food also affects palatability. Cats are unable to chew effectively. They reduce the size of the food by tearing or cutting it into pieces which can then be swallowed. The moisture content of the food influences the meal size and speed at which the food is eaten. Moist, palatable canned food is eaten rapidly when it is first offered although this gradually slows down over the mealtime. In contrast the more calorie dense dry foods are consumed at a slower, more constant rate. Semi-moist foods are consumed at a rate intermediate to the canned and dry foods. However, when food is offered ad lib, the pattern of feeding remains constant with small discreet meals being taken at random. The overall energy intake is rarely affected by the texture of the food.
Temperature also plays an important role in food selection. Most cats prefer food at temperatures around 35 degrees centigrade. This preference may be partly explained by the increase in food odour that occurs as the food is warmed but it is perhaps more than coincidence as this temperature is similar to that of freshly killed prey. As temperatures rise to about 40 degrees centigrade, the preference for the food decreases.
Previous experience
A cat's preference for food types is influenced by genetic and acquired feeding traits. Inherent patterns of behaviour play a large part in discriminating useful foods, as is indicated when orphaned kittens are being raised by hand without the benefits of learning from their natural parents. However, the individual cat's likes and dislikes for certain foods are influenced through the types of food experienced through its life.
Cats do like variety in their diet and will often choose a new diet in preference to a familiar one, as long as the difference is not too great, or the palatability too low. As the cat is a true carnivore, the different food items which are acceptable to it all tend to be very similar. This may explain why total aversion to a newly encountered food is not commonly found in the cat unless it is very different to its normal food, or of low palatability. If the cat is initially reluctant to accept a new food, this can often be overcome by offering several small meals of fresh food on subsequent occasions, thereby maintaining high odour levels.
The selection of food items may also be related to the motivational level of the cat. When under stress adult cats tend to select familiar food items rather than a new diet and may reject foods which have recently been associated with a stressful or painful event. Cats may also reject diets that are deficient in certain minerals and vitamins, such as thiamine. Cats probably recognise deficient foods via learned aversion. This appears to occur due to a linking of the flood flavour with an unsatisfactory digestive consequence, that is a rapid learning of flavour associated with a physiological response.
There are many other factors which can affect the feeding pattern of cats. Many cats are sensitive to lighting and noise levels, so the place of feeding may also be as important as the type of food container used and its cleanliness. Physiological factors, such as age, health and sexual activity of the cat can also affect appetite. The ability to appreciate taste and smell deteriorate with age and are reduced by certain disease conditions such as cat 'flu.
Stress associated with physiological factors such as new surroundings when moving house or being boarded or hospitalised may reduce food intake as may the introduction or loss of either a human or animal in the cat's environment. Short term veterinary treatment, such as castration or the lancing of an abscess, does not usually interfere with feeding patterns, however more prolonged medical interference can reduce appetite.
Energy needs
Many cats control their energy intake regardless of differences in the energy density, moisture content and texture of the diet. In general cats will normally eat the amount of food required to satisfy their energy requirements. Cats that hunt for food or are normally outdoors for long periods of time tend to take larger meals, but less of them. However cats readily adapt to different feeding schedules and if set feeding times are used then they will normally adjust food intake to accommodate this. The energy in food is measured in kilocalories (kcal) and is derived from fats, carbohydrates and protein. It is important that the percentage of energy provided by the protein part of the diet is at least 25% of the whole, otherwise the cat's appetite will be satisfied before it has taken in enough protein for its health requirements. Similarly it is also important that the food intake level is sufficient to supply the other necessary nutrients such as fats, carbohydrates, vitamins and minerals.
Types of nutrients
Protein
Protein is necessary for life, which is true whether the species is man, dog or cat. Proteins are large complex molecules which consist of chains of much smaller building blocks called amino acids. Cats, like other animals, require protein in their diet to provide the specific amino acids which their bodies cannot synthesise, these are referred to as the essential amino acids. These are then reformed into new proteins which are necessary for tissue growth, repair and the regulation of metabolic processes.
The cat has been shown to have a higher dietary protein requirement than the dog in both the adult and growth stages of development. This does not seem to be due to a high requirement for one or more particular amino acids, but because its metabolism appears to be set at a high rate of breakdown for amino acids which increases the demand for protein. Unlike other species which can adjust their rate of protein breakdown, cats seem to be unable to 'switch off' these mechanisms when presented with a low protein diet. This may be because the cat had little 'pressure' during the course of evolution to adapt to a low protein diet because of its efficient predatory behaviour which has ensured a high protein meat diet. Furthermore, animal flesh is low in carbohydrate which is the usual source of blood sugar in non-carnivorous species. Due to the cat's high intake of animal tissue, the ability to break down large quantities of protein to glucose is essential and may also help to explain the high protein needs of the cat. It is therefore recommended that the protein intake for the adult cat provides at least 25% of the daily calorie intake.
Fats
Dietary fats perform several functions They are the most concentrated energy source of all nutrients, and increase palatability and texture to cat foods. They are also important in carrying the fat soluble vitamins, A, D and E. Fat is essential to the cat's diet as it supplies the essential fatty acids (EFAs), linoleic and arachidonic acids, which play key roles in maintaining the general health of the cat and are vital in many body systems including the skin, kidneys and reproductive organs. In most mammals linoleic acid can be converted into the other EFAs required by the animal. The cat has a limited capacity to do this and whilst this may not seriously affect the health of the adult cat it does affect specific life stages such as reproduction. Linoleic acid is found in large amounts in plant oils but the EFAs derived from it are found almost exclusively in animal tissues. However, small amounts of linoleic acid are also found in meats and arachidonic acid is found exclusively in meat, making meat the best source of fat for cats. It is recommended that at least 9% of calories should be provided by fat.
Carbohydrates
The cat has no nutritional need for carbohydrate as it is able to derive a lot of its energy from the breakdown of protein. It does, however, have the necessary enzymes to digest and metabolise carbohydrates so they can form a useful dietary source of energy. Cats can therefore be fed wheatflakes, cooked rice and even potatoes to a limited extent, although some cats cannot tolerate high concentrations of certain sugars. For example, if suddenly given a large bowl of milk, some cats can develop diarrhoea from the sugars (sucrose and lactose) due to the lack of digestive enzymes resulting in fermentation of the sugars by bacteria in the gut. There are milk drinks designed especially for cats that are lactose reduced.
Vitamins
Studies in man and animals indicate that the so-called antioxidant vitamins, C, E and beta carotene (the precursor of Vitamin A, present in certain plants, vegetables and fruit) are important in preventing certain substances called free radicals from causing damage to cells and being involved in the ageing process. Vitamins may also be protective against certain forms of cancer.
Vitamin A
Vitamin A is best known for its importance in vision. It is also involved in other processes such as the regulation of cell membranes and the growth of bones and teeth. Beta carotene found in plant material, is used by many mammals as a precursor of Vitamin A. The cat, however, is unable to convert beta carotene to vitamin A and must therefore obtain its vitamin A from animal sources. Good sources for the cat are organs such as liver and kidneys, with muscle tissue being relatively low in this vitamin. However, a word of caution is necessary here, too much vitamin A can be as harmful as too little, and cats fed diets consisting mainly of raw liver have developed a condition known as hypervitaminosis A, presenting with signs of lethargy, unthriftiness, stiff neck and other skeletal problems. The daily requirement for an adult cat is in the region of 650-850 International Units which is present in only 5g of good quality beef liver.
Vitamin D
Vitamin D is involved in the metabolism of calcium. Animal tissue is low in calcium so the cat's diet must be supplemented with this mineral. A deficiency of vitamin D results in rickets. However, cats need very little vitamin D and when the quantity and ration of calcium to phosphorus in the diet is normal, true rickets is very rarely seen.
Vitamin E
Although very uncommon, vitamin E deficiency can occur in cats, particularly when fed food containing large amounts of unsaturated fats to which antioxidants have not been added. Unsaturated fats oxidise and go rancid easily, as a result, the vitamin E present is destroyed. Yellow fat disease or steatitis occurs due to a deficiency of vitamin E and may occur when feeding red tuna which does not have the necessary antioxidant or extra vitamin E added. Normal diets and proprietary foods containing tuna fish are adequately protected in this respect.
Vitamin C
Cats do not need to be fed vitamin C as they are able to produce their own.
B-group vitamins
The water soluble vitamins that are of relevance to cat nutrition are all members of the B-group or complex, and nearly all are involved with the utilisation of foods and the production of interconversion of energy in the body. Vitamin B1, or thiamine, is needed in relatively large amounts by the cat. Because it is progressively destroyed by heating, pet food manufacturers add calculated amounts in the pure form to the food being processed. Exactly the same progressive destruction occurs in any cooking operation so home cooked meats will need to be supplemented. Raw fish diets may also result in a deficiency of B1, due to the presence of thiaminase which destroy the vitamins.
Minerals
Minerals can be divided into two groups, the major or macro minerals which are required in larger quantities and the micro or trace minerals which are required in much smaller amounts. Almost all (about 99%) of the cat's body calcium is contained in the skeleton and teeth. Soft tissues such as meats and offal are very low in calcium and if they are fed as the sole food source, calcium deficiency will occur. Proprietary prepared foods from reputable manufacturers are supplemented as necessary during manufacture. Milk is a good source of calcium, unfortunately some cats are unable to tolerate the sugar present in milk (lactose) because of an inadequate amount of the enzyme lactase, which is important in lactose digestion. Some cats, especially of the Siamese breed, will not drink milk at all. Good proprietary diets have adequate supplies of the major and trace minerals.
Water
Water is the single most important nutrient necessary to sustain life. In spite of popular belief, cats require fresh clean water throughout a 24-hour period, even if they are drinking milk as well.
Obesity
If the cat is being fed individual meals several times daily, there is often a tendency to offer the daily supply of food on several occasions rather than divide up the daily feed into several meals. This can also occur with cats fed dry food ad lib. Cats usually regulate their food intake, but continual exposure to large quantities of food may lead to over-eating and subsequent obesity if too many calories are consumed. Monitor your cat's weight and ensure it does not become fat.
Kittens
At birth kittens on average weigh about 100g (about 3-4 ounces). They then show a phenomenal growth rate, the birth weight is doubled in the first week and they increase in weight by about 100g/week up to about 6 months of age. Because of the nutritional burden this places on the lactating queen, kittens should be encouraged to begin eating solid foods from about 3 weeks of age with weaning completed by 8 weeks of age. The solid food offered must be soft, palatable and offered in a shallow dish. As the interest in and ability to take solid food develops, they will reduce their demand on the queen for milk and her production will fall. Ideally the kitten should be weaned onto the food which will form its diet until fully grown.
To be suitable for kittens a food must meet a number of criteria. It must be highly digestible and have a smell, taste and texture which encourages the kitten to eat. Dry food such as kibbles may also be fed as they are high in calories, however it may be necessary to soak them in water or a little milk first. Following weaning, kittens should continue to be fed all they will eat of a good quality prepared cat food designed for growing kittens. Excessive calorie intake, growth rates and obesity do not generally occur in the growing kitten. Since they have relatively tiny stomachs, kittens should be fed small meals at regular intervals. Four or five meals are recommended at eight weeks of age, decreasing to two at six months of age.
Implications for feeding healthy and sick cats
The study of the feeding behaviour of cats has many applications for the cat owner. Odour, texture and temperature of food are important factors in the cat's feeding behaviour and can be manipulated to tempt the problem feeder or sick cat. When feeding the sick cat there are several ways in which the feeding regime can be manipulated in order to tempt food consumption. Offering palatable food with a strong odour will help to initiate feeding, and warming the food to about 35 degrees centigrade should also increase the odour produced by the food. Consequently food that is stored in a refrigerator should be warmed first or at least allowed to reach room temperature before being offered.
When food is left to stand in a dish the odour released decreases during the day making the food less appealing. Therefore with problem feeders offering regular small quantities of a warm palatable food may improve consumption. Increasing the amount of flavours (by feeding different varieties) and textures (dry and canned) in the diet may also increase food intake.
If a special diet is required in the management of a disease condition, it is preferable to introduce it gradually while the cat still has access to its original diet (unless contraindicated on medical grounds). This process allows the cat to become familiar with the new diet and learn that it is safe to eat. However, failure to eat a new diet may be associated with low palatability rather than by unfamiliarity to the food. Finally, as a familiar diet is preferred at times of stress, owners should ensure that an acceptable diet is available for their cat when it is placed in a different environment, such as in a cattery.
