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About

Canine Fur

What's fur?

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• Introduction
• Hair by any name
• Whiskers
• Color is not all black and white
• Coat problems

Introduction

Summertime, and the dog hair tumbleweeds roll across family-room floors in hundreds of thousands of households across the US. Wispy scraps of soft, fluffy undercoat and stiff strands of guard hair wend their way under furniture, cling to carpets and clothing, and invade cabinets and closets. Errant hairs find their way into the refrigerator to decorate a bowl of pudding or add protein to a salad. Vacuum cleaners are permanent fixtures in the corner to make it easier to suck up the hair several times a day.

All over the country, pet owners are grooming their retrievers and setters and spaniels and shepherds and northern breeds, loosening great avalanches of fur. An accumulation of hair through the month or so of shedding season looks like enough to knit a whole other dog or at least to stuff a set of throw pillows for the sofa.

Then, just when owners think they can't stand another minute of crumbling canine coiffures, the shedding stops, the new coat gradually fills in, and Mom can put the vacuum cleaner back into the closet.

Although admittedly a source of frustration during shedding season, dog hair is a marvelous body structure efficient at insulation, skin protection, and sensory perception.

Hair by any name

All mammals have some sort of hair covering some, much, or virtually all of their bodies. The hair on some animals, particularly those traditionally trapped for their pelage, is known as fur, but it's all the same no matter the name.

Hair is made of the protein keratin and dead epidermal or skin cells and it grows from follicles in the dermis or inner layer of the skin. Some hairs are densely packed into stiff, fibrous outgrowths that, depending on species and location on the body, become horns, fingernails, and toenails.

Human follicles each give rise to a single hair, but animals that depend on fur coats for temperature regulation often have several or many hairs per follicle. The diameter of individual hairs decreases as the number of hairs per follicle increases.

Each follicle has an oil or sebaceous gland to keep skin and hair smooth and elastic. Dog breeds developed to work in water generally have a high oil content in their coat so that water runs of the guard hairs and does not penetrate to the skin.

Dogs have three types of hair: soft downy undercoat that is especially abundant in northern breeds but exists in most breeds that developed in cool or cold climates; stiffer and often longer guard hairs that form a protective layer to protect undercoat and skin from harsh weather and cold water; and whiskers, those specialized hairs that grow in clumps on the face.

Dog hair grows in cycles; when it reaches a certain length determined by the individual dog's genetic makeup, it stops growing, then dies. That's when shedding begins. Sassy may be slightly uncomfortable during shedding as the dead hairs can cause her skin to itch. Her owners can help relieve that slight discomfort by brushing her coat.

Shedding seems to be connected to seasonal temperature, but it is actually governed by photoperiod or day length. Dogs that live outside usually shed heavily as days lengthen in spring, but those that live mostly indoors often seem to shed at least a bit all year. Loss of the winter undercoat helps the dog stay cooler in warm, humid weather, a necessity for an animal whose only sweat glands are in the pads of his paws. Female dogs often drop their coats after a heat cycle or after whelping and most dogs will also shed after undergoing anesthesia.

It is in winter that the dog's coat does its job. Muscles in the skin allow Bear to fluff his coat up, thus trapping a layer of air warmed by his body temperature between the skin and the environment. Thus shielded, Bear can choose a spot out of the wind, curl up in a ball, tuck legs under his body, cover nose with tail, and sleep outside in below-zero temperatures.

Hair also protects Sassy from injury to feet, eyes, and ears. Northern breeds tend to have hairy paws to protect their pads from ice and snow. Some breeds have hair inside their ears or across their eyes to protect those tender parts from debris.

Whiskers

Whiskers are the stiff hairs on the dog's face. They occur in clusters and serve as sensory structures — anything brushing against these whiskers stimulates Rusty to close his eyes, pull away, turn his head, paw his face, or shake his head.

Some exhibitors trim the whiskers of their show dogs, but such trimming may limit the dog's response to his environment and detracts from the natural appearance of the pet.

Color is not all black and white

Skin and hair color come from special cells in the skin that produce melanin according to Mischief's genetic code for color, and the amount of melanin is governed by the animal's genetic code, a complex genetic interaction of several pairs of genes that determine color, pattern, and distribution of white hairs on the body. Some breeds carry the genes for only a single color (West Highland White Terrier, Sussex Spaniel, Kuvasz, Maltese), some carry the code for several shades of a particular color (Golden Retriever, Weimaraner, Rhodesian Ridgeback) or are limited to a single two-color pattern (Rottweiler, Black and Tan Coonhound), and others (Akita, Greyhound, Whippet, Bulldog, American Staffordshire Terrier, Staffordshire Bull Terrier) carry a wide range of color and pattern possibilities.

A handful of breeds comes in merle or dapple patterns in either red or black. Merle pattern can be linked to health problems in Collies, Shetland Sheepdogs, Great Danes, and Dachshunds, including deafness and blindness. White coat in Dalmatians and Boxers is also connected with deafness.

Basic coat color research in dogs was done by geneticist Clarence Little ScD in 1957. Little identified 10 sets of genetic markers for color type, distribution, intensity, black masks, changes as the dog grows, dapple pattern, white pattern, and ticking pattern.

Dog hair can be black or brown (liver), red or yellow, white, or agouti (the “wild color” coat of Norwegian Elkhounds, some German Shepherds, etc. in which each hair has bands of different colors). Dog coats can also be spotted, patched, striped (brindle), or patterned with varying amounts of white.

Dogs with dilution factors in their color genes will be lighter versions of the basic body color. Those with white pattern factors will have more or less white distributed according to the distribution factors. So, Boston Terriers, Basenjis, and Corgis have definite white patterns, while some other breeds have white bodies with varying amounts of spotting or patches. Those with a color-aging factor may start out black and lighten to gray or blue (Kerry Blue Terrier) as a breed characteristic or as an individual trait (Akitas may be born black or deep brown and fade to some shade of red or silver or fawn over part or all of their coat).

To further complicate matters, the color of Butch's undercoat may be different from color of his guard hairs.

Coat problems

No matter what color Lad's coat may be, the condition of his hair mirrors the general state of his health. Thyroid problems, insufficient dietary fats, poor nutrition, hormone imbalances, seborrhea, ringworm, pore infections, hot spots, inhalant allergies, and external parasites can directly or indirectly affect hair health and growth.

Coat condition is, therefore, as important to monitor as appetite, behavior, and temperature when assessing Mango's well-being. A dull, dry, brittle, or greasy coat is a clue to the internal workings of the canine system.

Sources for this article include

• Dog Owner's Home Veterinary Handbook by Delbert Carlson DVM and James Giffin MD;
• Animal Life: Form and Function in the Animal Kingdom by Jill Bailey;
• The Inheritance of Coat Color in Dogs by Clarence Little ScD;
• Simon and Schuster's Guide to Mammals by Luigi Boitani and Stefania Bartoli.

Norma Bennett Woolf

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