Risk Factors

The skin is a major organ both in terms of surface area (1m2 for a 35-kg dog) and roles (social, maintenance of a stable internal environment, immune response, etc). In constantly rejuvenating itself the skin mobilizes a large part of the macro- and micronutrients provided by the food. An imbalanced intake of amino acids, fatty acids, vitamins or trace elements disrupts the barrier function (Table 1) and the immune protection provided by the skin. The dog may become more sensitive to infection and can develop allergic reactions more easily. The skin and the coat accordingly are the mirror of the dog's health and the quality of its food. There are many forms of nutritional dermatosis that frequently affect dogs (Table 2).

Nutrition has a special place in canine dermatology, not only as an essential factor in the prevention of skin diseases, but also as a therapeutic tool for allergy, keratoseborrheic and metabolic dermatopathies.

Pascal PRÉLAUD
DVM, Dipl ECVD

Pascal Prélaud graduated in 1984 from the Ecole Nationale Vétérinaire in Toulouse. In 1987 he founded CERI, a veterinary biology laboratory in Paris, which he continues to direct. This laboratory was a pioneer in the field of allergic testing in Europe. Pascal has worked as a specialist in veterinary dermatology since 1987. He now works in the Paris region. A member of the International Task Force on Canine Atopic Dermatitis, he is the author of many scientific articles and lectures, mainly on allergic dermatopathies in dogs and cats. He has authored two books on veterinary allergies (1991, 1999) and a book on endocrinology (2002), which has been translated into several languages. Pascal Prélaud is co-author of the Guide de Dermatologie Féline (2000) with Dr. Eric Guaguère.

Richard HARVEY
BVSc, DVD, Dipl ECVD, FIBiol, PhD, MRCVS

After obtaining his degree in veterinary science from the Bristol University in 1978, Richard Harvey spent ten years at a general practice, before moving to a small animal practice. Richard became a Diplomate of the European College of Veterinary Dermatology in 1993. He obtained his PhD in 2000 for his work on staphylococci and the dog's skin. Richard has published thirty scientific articles and co-authored three books, the most recent of which is about ear complaints in dogs and cats. Richard is also the editor-in-chief of Waltham Focus magazine.

1. Risk Factors

The risks of developing nutritional dermatoses are not only related to the quality of the food, but also to individual factors in the animal such as the physiological stage, the type of hair and the predisposition to certain metabolic or allergic diseases.

Breed Specificities

There are many breed-related predispositions in canine dermatology that can be directly linked to nutrition (Table 3).

The two main groups of nutritional dermatoses (zinc or vitamin A responsive dermatoses) are the major causes of keratinization problems in predisposed breeds (e.g., Nordic breeds with respect to zinc).

There is a higher likelihood of dietary hypersensitivities in breeds suffering from malassimilation and atopy.

In dogs with a dense coat (e.g., Pomeranian, Spitz, Shih Tzu), the quantity of hair is such that skin and coat maintenance and rejuvenation of the skin and coat accounts for 30 - 35% of daily protein requirement (Mundt & Stafforst, 1987). It is possible that the nutritional requirements of animals with a long coat and dense undercoat exceed that of shorthaired breeds.

Coat

The influence of nutrients on the color of the coat is well known. The coat's pigmentation depends on the presence and the distribution of pheomelanin (yellow-red) and eumelanin (black) pigment grains in the cortex and/or the medulla of hairs and along the pilary stem. The synthesis of these pigments depends on the intake of aromatic amino acids (phenylalanine [Phe] and tyrosine [Tyr]) and the activity of the tyrosinases (cupric enzyme) (Figure 1).

Figure 1. Synthesis of melanin from phenylalanine.

Dietary imbalances in animals with a dark or black coat may provoke the reddening of the coat (Busch-Kschiewan et al., 2003). This was initially shown in cats. In cats a slight imbalance in the aromatic amino acid intake may provoke the appearance of neurological problems (sensorial neuropathy) (Dickinson et al., 2004) and lightening of the coat in red cats, or the reddening of the coat in black cats (Yu et al., 2001).

Reddening is also a common pigmentation anomaly in large dogs with a black coat. Work conducted on Newfoundland puppies and black Labrador puppies (Zentek et al., 2003) shows that, in canines too, the level of phenylalanine and tyrosine needed to guarantee optimal coat pigmentation is twice that of the minimum requirements to ensure the puppy's optimal growth. They also showed that tyrosine supplementation in food helps increase the intensity of coat color (Figure 2). The nutritional recommendations based on the study of growth (NRC, AAFCO) do not allow estimation of the requirements necessary for some metabolically intense functions such as the production of melanine.

Figure 2. Influence of dietary tyrosine intake on color intensity in black dogs.

Over a 6 month period, these dogs have consumed the same diet, differing only in tyrosine and phenylalanine content (Tyr + Phe). From the left to the right, the (Tyr + Phe) intake represents 3.2, 2.6 and 1.9 times the estimated AAFCO requirement for growth. The effect of the diet is obvious: the black color is more intense in the dog on the left whereas, on the right, the growing hair have a reddish color. (© Royal Canin).

Age and Physiological Condition

The age or the physiological condition may influence the relationship between skin homeostasis, coat quality and food.

In dogs, immaturity of the immune system and high intestinal permeability may to some degree explain the prevalence of dietary hypersensitivities in the young animal (Day, 1999; Prélaud, 1999) as it does in humans (Chehade & Mayer, 2005). These phenomena may be more common during weaning.

Nutritional deficiencies appear more readily when the dogs' nutritional requirements exceed simple maintenance requirements: for example chronic disease, during gestation, lactation and growth, and especially in large-breed dogs. These deficiencies in protein, essential fatty acids and zinc, may result in keratinization defects.

In aging dogs, malassimilation is characterized by imbalances in the intake of polyunsaturated fatty acids.

Concurrent Diseases

Any disease that disrupts the assimilation of nutrients may have direct and indirect consequences on the quality of the coat and favor the development of concurrent diseases. Malassimilation is frequently associated with a dull and dry hair coat or even recurrent bacterial infections. Defective protein digestion may cause a decrease in immune tolerance as clearly demonstrated in human and murine models.

In dogs, this phenomenon is frequently described in German Shepherds with exocrine pancreatic failure (Biourge & Fontaine, 2004; Wiberg et al., 1998) and Soft Coated Wheaten Terriers suffering from protein-losing enteropathy (Vaden et al., 2000), which often develop digestive hypersensitivities with cutaneous manifestations (pruritus, recurring pyoderma). Chronic digestive problems or prolonged use of antibiotics may also provoke a deficiency in B vitamins and a secondary deficiency in polyunsaturated fatty acids (PUFA).

At birth the skin is very supple and the number of hair follicles is low. The fragility of the skin and the coat means that the puppy is very susceptible to attacks on the skin by parasites or infections. During growth the dermis thickens, the sebaceous glands increase in size and the hair follicles multiply: they increase by 50% in the Miniature Poodle between week 10 and 28 (Credille et al., 2002). The composition of skin lipids is also modified (Dunstan et al., 2002).

Dietary Balance

Poorly balanced nutritional intake may generate spectacular dermatological imbalances. The most common are due to generic foods that are low in fat with excessive mineral supplementation, the most common being surplus calcium which inhibits the absorption of zinc(Table 4).