The eyes may be the windows to the soul, but the condition of a dog’s coat and skin give a better indication of his overall nutritional status. The skin is the largest organ of the body and when it is not getting the nutrition it needs, problems are readily observed. Nutrition plays a key role in maintaining healthy skin and coat condition in dogs and cats. The coat of an animal is its first line of defence. Maintaining a coat that is healthy in appearance is important to the animal and to the pet parent for aesthetic reasons.
The skin, the largest organ in the body, serves as the second barrier to outside antigens. Cracks in the skin may allow bacteria and toxins from the environment to enter the body. The health of both the skin and coat of dogs and cats is affected directly by the nutrition of the animal. Therefore, feeding a complete and balanced diet is critical in maintaining skin and coat health.
Nutritional deficiencies and excesses, both can have detrimental effects; however, genetic defects in some animals may also result in a decrease in absorption of some essential nutrients needed for optimal skin and coat health. The most notable nutrients involved in skin and coat health include protein, fatty acids and zinc, as well as select vitamins and trace minerals.
Know more about your dog’s skin…
Adult skin is composed of three layers: the epidermis, the dermis and the hypodermis or subcutis.
Epidermis: The epidermis is the outermost layer of the skin. All epidermal cells are derived from the basal membrane (stratum basale), which is composed primarily of keratinocytes although other cells, including melanocytes, are also present. Keratinocytes have many functions, including production of keratin, a fibrous, sulfur-containing protein; and production of a lipid secretion which has an integral role in the regulation of the stratum-corneum barrier function and desquamation.
Dermis: The dermis supports the epidermis and consists of a matrix of collagen and reticular and elasticin a ground substance of chondroitin sulfate and hyaluronic acid. The tensile strength and elasticity of the skin is largely attributable to the dermis, which is also responsible for the maintenance and repair of the skin and modifies the structure and function of the epidermis.
Hypodermis: The underlying hypodermis is made up of loose connective tissue, elastic fibers, and variable amounts of fat. This layer acts as an energy reserve, as an insulator, and as protective padding and maintains the body contours.
Know more about your dog’s hair…
Three types of hair are present in dogs: the primary or guard hairs; the fine secondary hairs; and the tactile or sinus hairs, including the whiskers, which are responsible for the perception of touch. Each hair is divided into a free part or shaft, and a proximal part and root.
The hair is housed in an epithelial pit called a hair follicle and is attached, via the hair bulb, to the dermal papilla in the base of the follicle. It is here that mitotic activity occurs, which leads to the production of the hair matrix. Melanocytes, which produce the pigment melanin, are situated in the hair bulb.
Associated with the hair follicles there are:
- Sebaceous glands, except in the footpads or on the nose, which produce sebum.
- An erector pili muscle which elevates the hair and helps in the expression of sebum.
- Apocrine sweat glands (except in the skin of the footpads and nose), which predominantly function as pheromone secretory gland, rather than a thermoregulatory action.
- Eccrine sweat glands (only in the skin of the footpads), which are activated under nervous control, particularly in stressed or excited dogs.
Functions of skin and coat…
Major functions of the skin and coat include:
- Maintenance of an enclosing natural barrier between the animal’s internal environment and the outside world.
- Preservation of the animal’s shape.
- Protection against water loss
- Protection from physical, chemical, and microbial injury imposed by external agents.
- Storage of nutrients.
- Sensory perception.
- Vitamin D synthesis.
- Important indicator of health status.
- Significant role in communication (e.g., pilo erection, excretion of pheromones).
- The protective function of the skin and coat is enhanced by the presence of an emulsion of sebum.
This emulsion also provides a physical barrier, maintains skin hydration to keep it soft and pliable, spreads over the hair coat to produce a glossy sheen, contains antimicrobial substances and is immunologically active.
Different minerals for maintaining healthy skin and coat condition…
Some of the different minerals required for a healthy coat and skin include:
Zinc is a transition metal found throughout the body. It is present in most tissues in relatively low concentrations. Zinc is the co-factor for around 200 zinc-containing enzymes involved in cell replication, carbohydrate and protein metabolism, and membrane structure. It is essential for the transport of vitamin A in the blood and plays an important role in reproduction. It is also crucial for collagen and keratin synthesis and is therefore a fundamental element involved in skin and coat health, and wound healing.
Common sources of zinc: Whole grain cereals and meat are rich natural sources of zinc. Zinc can also be found in mineral salts such as zinc sulphate and zinc oxide.
Deficiency of zinc: Absolute dietary deficiencies of zinc are considered rare in dogs, but a relative deficiency may occur when the availability of dietary zinc is reduced through nutrient interactions or where intestinal absorption of zinc is impaired through disease or genetic factors.
Intestinal absorption of zinc can be inhibited by:
- Excessive levels of dietary calcium, iron and copper, which compete with zinc for intestinal absorption sites.
- High levels of dietary phylate, found in cereal-based diets, which chelates zinc.
- Inherent defects of zinc absorption.
- Prolonged enteritis or other malabsorption syndromes.
Most cases of zinc-responsive dermatosis in dogs have been associated with the feeding of poor quality, cereal or soy-based dry food, the effects of which may be exacerbated in some animals by other predisposing factors.
Lethal acrodermatitis is an inherited disease of English Bull Terriers in which a defect of zinc metabolism is thought to give rise to severe systemic, as well as cutaneous, signs that resemble experimental zinc deficiency. The condition is unresponsive to zinc supplementation and is usually fatal, with an average survival time of seven months for affected puppies.
Pathophysiology: Zinc plays a critical role in regulating many aspects of cellular metabolism, a number of which are concerned with the maintenance of a healthy skin and coat. It is an integral component of a wide range of metallenzymes and, as a cofactor for RNA and DNA polymerases, its presence is of particular importance in rapidly dividing cells, including those of the epidermis. Zinc is also essential for the biosynthesis of acids, participates in both inflammatory and immune systems and is involved in the metabolism of vitamin A.
Clinically, two zinc-responsive dermatologic syndromes are recognised, although there is considerable overlap between the two:
Clinical signs: Signs of zinc deficiency are confined mainly to the skin, but may be accompanied by:
- Growth and other abnormalities in young animals.
- Depressed appetite due to a diminished sense of taste and smell.
- Weight loss, impaired wound healing, conjunctivitis, and keratitis.
- Generalised lymphadenopathy, particularly in young animals.
Cutaneous signs are characterized by:
- Focal areas of erythema, alopecia, scale, and crust with underlying suppuration, which develop symmetrically particularly around the face, extremities, mucocutaneous junctions and pressure points of the limbs.
- Hyperkeratotic footpads with deep fissures.
- Dull and harsh hair coat.
- Secondary pyoderma.
The bodies of dogs and cats contain a very small amount of copper. In 1984, Meyer reported a total body content of copper to be 7.3 mg per kg body weight in young dogs.
Role of copper in the body: Copper facilitates the intestinal absorption of iron and its incorporation into haemoglobin. It is an active element in many enzymes. Copper plays an important role in reducing cellular damage caused by free radicals. Copper is also involved in the synthesis of collagen in the tendons and the myelin within the system. Copper also participates in the synthesis of melanin, which is a hair pigment. Common sources of copper: Foods that have high copper content include meat (lamb, pork, duck) and protein rich grains (peas, lentils, soy). Copper may also be added to pet food in the form of mineral salts, however, copper oxide is a poorly available form of this mineral. Deficiency of copper: Copper deficiency can result in anaemia, loss of hair pigmentation and hyperextension of the lower limb. Copper is stored in the liver and although toxicity is rare, certain breeds are pre-disposed to copper storage disease, for example, Bedlington Terriers; involved in tissue, pigment and protein synthesis Other minerals and vitamins Other minerals and several vitamins also may have an effect on skin and coat health. A deficiency in iodine, responsible for a normal functioning thyroid, will create skin lesions and poor hair coat. Although rare, vitamin deficiencies can result in several skin and coat problems. Vitamin A is important in proper keratinisation of the skin. Deficiencies will result in hyperkeratinisation, poor hair coat, and alopecia. Vitamin B-complex vitamins, namely biotin, will manifest similar deficiency symptoms as vitamin A. However, most lesions of the skin characteristically occur around the face and eyes. A deficiency is rare, although it may be caused in animals fed with raw eggs due to avidin, a protein that binds biotin, rendering it unavailable to the animal.
(Dr RK Yogi, Dr AK Singh, Dr Preeti, Dr AP Singh and Dr SS Kullu are research scholars at National Dairy Research Institute, Karnal).