Determinism and Regulation of Feeding Consumption

3. Determinism and Regulation of Feeding Consumption

External Stimuli: Picking the Appropriate Food

Cats appear to be sensitive to the odor, form, texture and palatability of their diet (Table 4).

Odor

Odor is key for cats: an off flavor arising from rancidity of fat can halt food intake regardless of the taste or nutritional value of the food. Odor is the major criteria of food selection. Experiments that alternated odor flow across the bowl of kibble have shown an increased numbers of meals and food consumption during the odor circulation phase.

Cats prefer food that is at room temperature or near body temperature (38 to 40°C), most probably because it contributes to volatilization of food odors. Temperature interferes with odor for volatilization of compounds. It is also something closer to prey temperature. In practice, increasing food temperature from 20 to 40°C can enhance food consumption up to 80%.

Prehension and mastication in the mouth leads to food re-warming. This can be important to get an improved perception of odors through retronasal olfaction.

Shape

Since prehension occurs before food enters the cat’s mouth, the ease of prehension is important to consider (see trials with Persians). For kibbles, shape determines the lines of breakage and convenience to guide toward the ancestral carnivorous drive, where it is broken in one strike before swallowing. Shape, by determining surface to volume ratio, also displays more or less flavors.

Texture

Some research has suggested differences in food preferences between domestic pet cats and freeranging cats living on farms (Bradshaw et al, 2000). Farm cats preferred raw meat diets while house cats preferred harder or drier types of food (e.g., kibbles). These data may reflect learned preferences and/or neophobia of a food choice that is provided infrequently as was the raw meat to house cats. Cats used to a certain texture or shape of dry kibble may refuse new diets that vary in either one of these dimensions.

The food most frequently offered to cats comes primarily in two forms, dry cat food and moist (canned or pouch) cat food. Cats like the "cracking texture" of dry kibbles and the high moisture content (75 - 80%) of canned food however, rehydration of dry food is not appreciated by cats, unlike dogs.

Dry cat food has certain advantages for the human caregiver:
- it is easier to store, to keep for a longer period of time
- it can easily be fed free choice without concerns of spoilage
- it may offer dental hygiene properties. The chewing and grinding may help prevent plaque and calculus development (see Chapter 10) and dry diets have been specifically formulated to increase their dental cleaning properties.

Some cats show a preference for certain shaped kibble morsels and have preferences for mouth feel and surface to volume ratio of the food (Crane et al, 2000). Cats reject broken kibbles.

Canned cat food can either be a complete and balanced diet or just a supplement that is primarily meat. Canned foods are blended and contain additional water; in some cases the moisture of the product reaches 85%. It can result in a low caloric density and thus promote higher intake on a long term basis Many cats find canned foods extremely palatable due to the high water, fat and protein content (Case, 2003). Product texture is very important to determine eating patterns:

Minced products are continuously swallowed, the cat staying crouched and never lifting its head. The speed of eating is high and owners may perceive that this is a reflection of palatability, whereas the reason is more mechanical than sensorial!

Jelly products lead cats to take large gulps of meat. They have to chew a bit and lift their head simply to swallow. Some owners may have the perception that their cat is more reluctant to eat. Others may feel that the cat is appreciating the food, tasting it quietly, thanking them by looking at them and licking their lips!

The texturometer is used to measure the kibble’s resistance to the force of the cat’s teeth and jaws. Interchangeable modules imitate the shape and size of teeth according to the size and age of the cat. (© Royal Canin).

Semi moist foods: most of these products are marketed as treats for cats and are not meant to be used as the sole dietary source of nutrition. They are softer in texture than dry food, but they are not as moist as canned food. They do not require refrigeration and have long shelf lives. Some ingredients, used as preservatives of the water level, may even negatively affect palatability.

Homemade diets are not usually recommended since cats have specific dietary requirements that may be hard to meet.

Taste and the Composition of the Food

Food palatability is the very first key factor of success for petfood acceptance, for both cats and owners. Despite a lot of publications concerning feline food preferences or aversions, cat’s preferences are more nutrient-orientated than ingredient-orientated. Quality and freshness of raw materials are nevertheless important.

An important technological know how (enzymatic hydrolysis, fermentation, etc.) has been developed, leading to the commercialization of very efficient natural flavors, homogeneously coated onto the kibbles in order to drastically increase their acceptance (Figure 8). However, there is little information that the authors can provide in this text as the data remains strictly confidential among palatability experts in petfood companies.

Figure 8. Main technologies used in the development of aromas.

Proteins (especially hydrolysed proteins from meats, and sometimes plants such as soyabean) as well as fat are both palatable for cats. Some ingredients like yeasts and specific acids are also appreciated by cats.

The selection of fat is important, and above all their protection against oxidation. Fat can also interfere with palatability through some texture effects. Short and medium chain fatty acids (caprylic acid, coconut oil, etc.) are sometimes associated with altering the palatability of the food (Mac Donald et al, 1985) but this effect can be hidden when the ingredients and the surrounding formula are appealing for the cat.

Palatability has too often been blamed for feline obesity. However, the food’s energy concentration is more important than palatability. An inactive, neutered cat that has access to food with a highenergy concentration will inexorably gain weight. Prevention is about maximizing activity and optimizing the composition of the food.

A cat has more difficulty limiting its food consumption if the kibbles are very rich in fat. Cats fed ad libitum with a food containing 20% fat develop greater adipose reserves than when the fat level is halved, regardless of the animal’s sex: male or female, intact or neutered (Nguyen et al, 1999).

Elements of the Regulation of Hunger

Global palatability of the food is crucial, but hunger is a sine qua non condition for the cat to eat.

General Principles

Energy supply is controlled by homeostatic regulatory processes for food intake and body expenditure or both. Nutrient supply to the body must be constant. However, food intake is a discontinued and periodic behavior. A medium and long term regulation system thus exists; with the involvement of body storages (essentially fat). Everything is done homeostatically to prevent loss of tissues and weight loss.

Controls of food intake can be classified by several pathways:
- Behavioral pathways: habits and learning such as sensorial or metabolic conditioning
- Nervous pathways: mastication effecting oral satiation, stomach filling effecting physical satiation
- Metabolic pathways: short term glucostatic theory, long term lipostatic theory

Glucostatic Theory in Cats

A low level of glucose in the hypothalamic cells triggers hunger (Rowland, 1985).

Lipostatic Theory

The endocrine role of adipose cells has been studied during the past few years. Many cytokines have been identified that act on insulin metabolism, inflammation, etc. Among these, leptin, the satiety hormone discovered in 1994, has been clearly involved in appetite regulation (Bouret et al, 2004) however, there are few studies in cats.

One satiation signal cannot act alone to control body balance which is the result of a series of separated control points, acting on a different time scale. Animals control their food consumption through 3 major food compounds:
- Water
- Sodium (all other mineral are consumed in relation to caloric density)
- Energetic nutrients

If formulation is correctly done and if the feeding distribution well adapted to behavior requirements, energetic regulation is then efficient.

It has been suggested that the sensorial properties of a food become more important than metabolic ones for deprived cats. This could be an adaptative protective behavior during which cats seeking desperately for food become more discriminating to avoid poisoning risks in excessive hunger states. For well-fed cats, both palatability and nutritional values are acting in the regulation process.

From a practical standpoint, the only valid clue of efficient regulation is the stability of body weight. Significant inter-individual variability does exist. When analyzing publications and the possibly contradictory conclusions, it is important to perform a critical evaluation of what kind of regulatory processes are explored in relation to the beginning (animal reaction), the duration (constant modification) and termination (new equilibrium status).

Energy Regulation

Many experiments on caloric dilution of food content have been performed. Some contradictory conclusions have been drawn, that are often linked to the methodology employed (e.g., the addition of cellulose, water, clay etc).

Under very stable conditions, the cat seems able to control its food intake in relation to caloric density (more precisely in relation to dry matter caloric density). This process starts within 2 to 3 days and requires at least 3 or 4 weeks (Rowland, 1981). Meal size is most affected, secondarily meal frequency. However cafeteria feeding (i.e., changing and varying daily dry matter content and palatability) disturbs this natural ability. This is typically what happens in the home when the owner frequently alternates canned and dry foods, brands, varieties, etc.

Protein Regulation

In cats, contrary to humans or dogs, protein has been shown to increase food intake (Servet et al, 2008). Therefore, limiting the amount of protein (with a fiber substitution) is an original strategy to limit spontaneous food/energy intake. These observations might be useful in the design of a diet to manage feline obesity (see Chapter 1).

It has been suggested that some specific amino acids, such as tryptophan can affect general behavior (agression, excitability or territoriality modulation) in dogs (Bosch et al, 2007). There may be a relationship between tryptophan intake by the brain and the level of carbohydrate in the diet. However, changes of the level of carbohydrate in the diet are often linked to concommittant change in the protein level, which can also affect behavior. The mechanism how the intake of nutrients that act as precursors of neurotransmittors (choline for acetylcholine, tyrosine for catecholamines, and tryptophan for serotonin) effect food composition is unclear and obviously needs more scientific work.

Why Do Some Cats Like Fish So Much?

In its original environment – the cat is adapted to deserts – where there is limited availability of fish. So where does this attraction for fish flesh come from - even to the extent that certain cats take great delight in raiding garden ponds, and feasting on gold fish and young koi?

© É. Malandain.

Fish is a source of protein. Historically, cats have always been very opportunistic and quickly realized that there was obvious benefit in hanging around the quays when fishing boats returned to port because they could eat the remains from cleaning and gutting of the fish. In the time of sailing boats, voyages took a long time and boats took on board provisions of cereals - unfortunately accompanied by mice and rats that fed on them. Cats were therefore taken on board as well in order to control the population of these undesirable rodents and, once their mission was accomplished, the sailors would therefore show their gratitude by giving them fish.

In Asia, similar to human food, ocean-products are very commonly used in catfood.

Physical Satiety

It has been proposed that the receptors for physical satiety in cats may be more efficient in regulating food intake than the energy pathways. In the single meal feeding situation, the cat is able to achieve its daily needs, even within 5 days following a transition from ad libitum to one hour distribution (Thorne, 1982; Finco et al, 1986).

Ranking of control pathways is logically linked to the action level: physical satiation in the short term and caloric satiation in the medium term. The link is the fact that dry matter is both responsible for filling the stomach and for providing energy.

From a developmental standpoint, experiments on new born kittens (Hinde, 1975) would suggest that oral satiation is acting first before the development of gastric satiation: in other words, milk intake is less important than suckling movements.

Sleep is increased after meals. The effect is noticeable 3 hours after intake. Latency is variable: the quicker it appears, the longer it lasts. It is medidated by endocrine pathways and depends upon nutrients, duodenum pH, and gastric emptying.