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This paper addresses the question as to whether panels are needed to develop palatable and healthy pet food, a simple question which is difficult to answer. Panels for nutritional purposes usually consist of palatability trials, digestibility trials, trials to evaluate faeces quality and urine composition. Besides those routine investigations, trials are conducted to answer special questions, e.g., questions about the effectiveness of functional ingredients or availability of certain compounds.


Purchase criteria

The production of a palatable and healthy pet food requires special knowledge and skills. During the last 50 or more years much research has been done in this field and that work continues. The aim of pet food companies is to produce food that is accepted by pet owners as well as pets. Selection of pet foods is difficult for inexperienced pet owners. The following criteria may be crucial in decision making:

• Acceptance of the food by the pet: Feeding an animal is of major importance for the social interaction between the owner and his pet. Because giving unpalatable food is usually frustrating for both the owner and the animal, palatability is an important criteria in food re-purchasing. Thus, palatability is also one of the most important criteria in diet formulation for pets, especially for cats.
  
• Workload associated with food preparation: Commercial foods require less work compared with homemade foods. Thus, most pet owners refuse to make homemade food. Just a few owners, normally elderly people, prefer to cook for their pets.
  
• Food costs: According to our experience, food costs play no role for cat or small breed dog owners. Conversely, owners of middle and large breed dogs are interested in feeding middle or low price foods. Therefore, larger breeds commonly are fed dry food, which is cheaper than canned food and often even cheaper than homemade diets.
  
• Food tolerance: For pet owners, an obvious criteria to evaluate food tolerance is faeces quality. Faeces quality is an important determinant as to whether to feed the same food over a long period. Sometimes owners test three or more different foods until they find an acceptable one. Owners expect that a healthy food produces faeces that are of a well-formed and dry consistency. The amount of faeces dogs produce is also of interest to owners as sometimes they complain about large amounts and take this as a sign of low quality food. A further sign of food tolerance is skin and coat quality. Adverse reactions to food or poor coat quality are often implicated in food intolerance or poor food quality. In addition, the odour of the dog sometimes changes when food is changed and this characteristic can also be pivotal in repurchase decisions.
  
• Long-term impact on animal health and longevity: In this regard, owners have no outward signs that can give evidence about the food quality. Advertisements by the food manufacturer, experience and opinions of breeders or salespersons and also the veterinarian may have an impact on food choices of the owner. Special functional ingredients that the owner recognizes to be functional in human diets can make a contribution, also.

As described by Laue (2006) the food trends of human beings have changed over the years and those trends also have an impact on pet food trends; and companies take advantage of those trends. In either case, pet food companies must win the confidence of pet owners. In view of the importance pets have to some owners as a partner or even as their only partner, pet food producers have a large responsibility.


Palatability

Palatability of food is influenced by many factors including food consistency, ingredients, special flavour, and finally, individual animal preference. Not only a change in food composition, but also a modification of food technology or packaging material can influence the taste of food. To find out more information about food acceptance, the scientific literature can be consulted.

Some trials deal specifically with the food preferences of cats. Typically, the influence of protein content, fat, food texture, moisture, specific amino acids, and specific acids (e.g., phosphoric and carboxylic acids) and other substances on palatability are tested (Zaghini and Biagi, 2005).

Palatability trials with a known pet panel can give some information about acceptance. Especially in cats, palatability trials give acceptable results, because cats are finicky consumers. On the other hand, they develop confirmed habits that affect their preference for taste as well as texture of food. It seems evident that cats living in regions with high fish consumption like fish more than cats that are used to meat. The food preferences of cats are influenced by the diet of the mother during pregnancy and lactation, and particularly the flavours the kitten experiences during the first months (Stasiak, 2001; 2002).

On the other hand, the results of palatability trials with Beagle dogs are sometimes unclear, and such trials must be carefully designed. Other dog breeds are probably more conducive to palatability trials than Beagles. Palatability test results should be interpreted with caution.


Faeces characteristics and quantity

A change in food composition or in food technology can influence faecal characteristics. Long-term study of the same group of dogs or cats can provide clear results concerning faeces quality. Digestibility trials can also provide information about faeces quantity, which is of interest in urban regions where faeces must be removed from streets.


Health considerations

An essential requirement of a healthy pet food is that the food provides all nutrients in a sufficient amount and that harmful nutrients do not exceed critical values. To fulfill these requirements would at first glance appear to be easy. Different organisations like NRC (National Research Council), AAFCO (Association of American Feed Control Officials), FEDIAF (The European Pet Food Industry Federation), among others, issue tables recommending the basic nutrient levels for cat and dog food. Nevertheless, recommendations can differ between organisations and recommended values can change dramatically from year to year based on the outcomes of research trials.

The nutrient content of food can be determined using laboratory techniques. However, laboratory investigations cannot give information about the digestibility and availability of nutrients and supplements. Nutrients in pet food must be available so that animals can absorb and metabolize them in sufficient quantity. The availability of nutrients in most of the compounds and feedstuffs used to prepare pet food is known. Either digestibility trials or metabolic trials are appropriate to assess availability of nutrients or minerals. To determine the availability of vitamins or functional ingredients other tests must be chosen.

Healthy nutrition is expected to increase longevity as well as quality of life. In this regard many questions remain unanswered, e.g., the effects of oversupply of certain nutrients or minerals and to what extent such imbalances influence the life expectancy of dogs and cats.

For example, some cat foods contain phosphorus concentrations that are three or four times higher than those required. Indeed, many publications address the phosphorus content in food in relation to cats suffering from chronic renal failure. Whether a high phosphorus level in foods for healthy, adult cats is a risk factor for renal failure is not yet established. However, the comparison of the life expectancy of dogs and cats living in the developed world with those living in developing countries shows us that, besides the abatement of contagious diseases and medical care, nutrition plays an important role in longevity.

Functional ingredients are becoming a more and more important criteria in pet owner purchase decisions. As shown by Cupp (2006), functional ingredients can increase the lifespan of cats. In this field, much research is needed to ensure the effectiveness and safety of these substances. Moreover, regulations demand test results before feed additives can be marketed. In fact, research work in the field of pet nutrition has expanded in response to regulations. To establish formulas for the prediction of food digestibility and estimation of food energy content based on crude nutrient content, a multiplicity of digestibility trials are necessary.


Conclusion

The knowledge that is currently available about the nutrient requirements of dogs and cats enables us to produce palatable and nutritious pet food without any trials. Regulations provide additional information about the use of certain compounds. The question remains whether we possess enough knowledge to produce ‘healthy’ food. The reasons for the emergence of diseases like inflammatory bowel disease in cats, which is brought on by the consumption of mainly dry food, or the increase in oxalate stone formation in dogs and cats need to be determined. Retrospective studies could provide information as to whether type of food can be a risk factor.

Looking to future market requirements, further research is necessary to react to these demands in a reliable way. Food for different stages of life, different breeds, and even different ways of life is not yet widely available. Without the use of panels, improvements in pet food quality and safety cannot increase. Ongoing research will be necessary in the future as well to extend our knowledge about the nutritional needs of our companion animals. “Let food be your medicine and medicine be your food.” These were the words of Hippocrates in 400 BC. This wisdom becomes more and more meaningful today, even for pets.


References

Cupp, C.J. 2006. Nutrient blend for prolonged healthy life in aging cats. Nestle Purina Nutrition Forum. Advances in Veterinary Nutrition. Lausanne, Switzerland, Oct. 9- 10.

Laue, D.K. 2006. Human consumer trends and elements in pet food. In: Recent Advances in Pet Nutrition (D.K. Laue and L.A. Tucker, eds). Nottingham University Press, UK, p. 9-18.

Stasiak, M. 2001. The effect of early specific feeding on food conditioning in cats. Dev. Psychobio. 39(3):207-15.

Stasiak, M. 2002. The development of food preferences in cats: the new direction. Nutr. Neurosci. 5(4):221-8.

Zaghini, G. and G. Biagi. 2005. Nutritional peculiarities and diet palatability in the cat. Vet. Res. Comm. 29(Supp. 2):39-44.

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