The hair coat sub serves many useful functions among which are protection from the outside environment (including light), regulation of body temperature, and sensation (tactile hairs or whiskers). Together with the skin it represents 24 percent of an animal’s body weight. Hair emanates from and is an extension of the skin, growing from follicles contained within the skin. Skin glands empty into the hair follicle along its course; some skin glands also directly open onto the skin surface. The follicles are oriented at an angle; the shape of the hair follicle determines whether the hair is straight, wavy or curly – straight hair coats are characterized by straight hair follicles while curly hair coats are characterized by hair follicles that undulate. Hairs grow in phases characterized as hair follicles being in a state of either growth, transition, or rest. In the summertime, approximately 50 percent of the hair follicles are growing; in wintertime, up to 90 percent of the hair follicles are growing. Hair coat length is determined by the genetically determined rate of hair growth as well as the duration of the growth phase. Nearby hair follicles are typically in differing phases of growth and rest. Thus hair growth is in a state of continual turnover, most but not all hair follicles are growing and not resting (even in the summertime) and there is a “grain” to the hair coat.
The hair coat is divided into primary hairs or long hairs and secondary and shorter hairs that form the undercoat. The long hairs can lie flat against the undercoat or are capable of changing position – erection that allows more air trapping to increase the insulation value of the hair coat. The secondary hairs are typically denser and weigh more than the primary hairs as both dogs and cats have higher numbers of secondary hairs in comparison to coarse hairs. Cats differ from dogs in that they have a third type of hair that is thinner yet than secondary hairs; these are called down hairs. Secondary hairs in cats are present in greater numbers in proportion to the coarser, outer guard hairs in contrast to dogs. Hair growth rates are essentially the same between dogs and cats, although certain dog breeds grow hair at a faster rate compared to cats. However, dogs will produce almost 2 times as much hair per year in comparison to cats. Hair regrowth rates following clipping can vary from 3 to 4 months for normal and short hair coat lengths, and up to 18 months for long hair coat lengths. Hair length can vary by region of the body but once the maximum and preordained length is achieved, no further growth occurs.
There are three major types of hair coats termed normal, short and long hair types. The normal hair coat type is typified by German Shepherds, Corgis and wild dogs. There are long hairs and larger numbers of secondary hairs that form the undercoat. The short hair type can be subdivided into a coarse or fine subtype. Coarse hair types are typical of the Rottweiler and the terrier breeds. The secondary hairs are fewer in number and weight. The fine hair type is typified by boxers, dachshunds and miniature pinschers. This group has the densest hair coat. Primary hairs are shorter and secondary hairs are more numerous. The long coated hair type can also be subdivided into either a fine subtype or a wooly or coarse hair coat subtype. A fine long coated type is typified by Cocker Spaniels, Pomeranians and Chow Chows. The hair coat is denser still than the normal hair coat type (except in the toy breeds) and is heavier by weight. The wooly hair coat type is found in Standard Poodles, Bedlington terriers and Kerry Blue Terriers. Three quarters of the hairs in this hair coat type are comprised of secondary hairs. These breeds also tend to shed less.
The goals of grooming then are to detangle, remove dead hair and if your pet is shampooed, to finish the grooming process during drying to prevent matting and tangling. Using the proper tool allows you to address differences in hair coat length and density without causing harm to either the skin or the hair coat. Using the wrong tool or applying too much traction to growing hairs or traction against the grain of the hair coat creates discomfort and causes inflammation and damage to the hair follicle. In the next article, we’ll review grooming tools and general care instructions for some common problems that you are likely to encounter with your pet.
Author: Robert Z Berry, DVM Source material: ”Mueller and Kirk’s Small Animal Dermatology” by Scott, Miller and Griffin.