Skin Appendages of animals

Hair follicles, oil and sweat glands, and hooves are all skin appendages that grow out of the epidermis and dermis. The hair follicles of horses are simple—the follicles have 1 hair emerging from each pore. The growth of hair is affected by nutrition, hormones, and change of season. The size, shape, and length of hair are controlled by genetics and hormones. Disease, drugs, nutrition, and environment also affect the health of hair. The hair coat protects the skin from physical and ultraviolet light damage, and helps regulate body temperature. Trapping air between secondary hairs conserves heat. This requires that the hairs be dry and waterproof. The cold-weather coat of many animals is often longer and finer to facilitate heat conservation. The hair coat can also help cool the skin. The warm-weather coat has shorter thicker hairs and fewer secondary hairs. This anatomic change allows air to move easily through the coat, which facilitates cooling. Oil glands (also called sebaceous glands) secrete an oily substance called sebum into the hair follicles and onto the skin. They are present in large numbers near the hooves, back of the neck, rump, mouth, and tail area. Sebum is important for keeping the skin soft, moist, and pliable. It gives the hair coat sheen and has antimicrobial properties. Sweat glands are part of the horse's system to regulate body temperature. They are found over most of the body except the legs. The evaporation of sweat from the skin is the primary cooling mechanism of the body for horses. Subcutis The subcutis is the innermost major layer of skin. It contains the subcutaneous fat and muscles. (The word subcutaneous means “beneath the skin.”) The twitch muscle is the major subcutaneous muscle. The subcutaneous fat provides insulation; a reservoir for fluids, electrolytes, and energy; and a shock absorber. Nerves and blood vessels that supply the skin are also found in the subcutis. Last full review/revision July 2011 by Karen A. Moriello, DVM, DACVD; John E. Lloyd, BS, PhD; Bertrand J. Losson, DVM, PhD, DEVPC; Wayne Rosenkrantz, DVM, DACVD; Patricia A. Talcott, MS, DVM, PhD, DABVT; Alice E. Villalobos, DVM, DPNAP; Patricia D. White, DVM, MS, DACVD; Thomas R. Klei, PhD; David Stiller, MS, PhD; Stephen D. White, DVM, DACVD; Carol S. Foil, DVM, MS, DACVD