The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.
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16 TheHorse.com THE HORSE June 2017 nerves, and "skin appendages." Its main function is to nurture the epidermis. Blood vessels supply nutrients and help regulate the horse's body temperature. Specifically, increased blood flow to the vessels in the dermis help dissipate heat during exercise, while blood vessel con- striction decreases blood flow to reduce heat loss through the skin. The nerve supply to the skin is impressive, allowing horses to rapidly respond to heat, cold, pain, and subtle pressures and touches. Our nerve supply is similar; think about the immediate reaction you have after touching a dish right out of the oven or slicing your finger on a piece of mail. Hair follicles, one of the major skin appendages, produce the individual hairs. Ancillary appendages include sebaceous glands that produce an oily substance called sebum. Sebum protects the skin by keeping it soft, moist, and pliable. It also possesses antimicrobial properties. Sweat glands, primarily located on the abdomen and thorax (and not the legs) also help control the horse's body temperature. As sweat evaporates, the body cools. LAYER 3: The Hypodermis The third and final layer, found beneath the dermis, contains fat, muscle (the twitch muscles, for example, that discourage insects from landing), blood vessels, and nerves. Life on the Surface So, we now know this outer layer— this collection of dead skin cells covered with sebum and punctuated with hair follicles—is protective, thermoregulatory, and infection-fighting. A population of microscopic organisms on the surface of the skin lends a helping hand. Just like the intestines are filled with millions of microbes that keep the horse healthy, the skin also has "normal" bacteria, viruses, and fungi (including yeast) residing on its epidermis. These microbes, called the skin microbiome, populate the skin's surface during and immediately after birth. They remain with the horse for the rest of its life. As commensals—organisms that live on or in a host with both microbe and host deriving a mutual benefit—they help prevent pathogenic (disease-causing) organisms from colonizing the skin. Dozens of bacterial species inhabit the skin, including Staphylococcus spp (even S. aureus, of MRSA infamy) and Strepto- coccus spp. More than 30 fungi species cohabitate with the bacteria, including Aspergillus, Candida, and Malassezia. Interestingly, certain types of bacteria and fungi prefer certain regions of the skin; some species choose to inhabit the armpit and groin areas, while others frolic on the back, head, or neck. Members of the skin microbiome can, in some cases, cause or contribute to certain skin diseases. When breaks in the skin or changes in the epidermal "envi- ronment" (the amount of sebum present, for example) occur, commensals can cause infection and/or disease. Pros and Cons of Bathing Depending on a horse's use, the num- ber of baths he gets can vary tremendous- ly. Some of us might have to wrack our brains to recall the last time we bathed our pony, whereas others give their babies a weekly spa treatment. Others still bathe them daily or even multiple times a day. Removing dried sweat, dirt, and debris is absolutely necessary, especially after riding. Foreign material between the horse and the saddle or boots can damage the skin, causing infection and pain and lost riding time. Grooming, not neces- sarily bathing, removes said debris, often preventing these insults. Routine groom- ing also allows us to examine our horse carefully from top to bottom for: ■ Cuts, abscesses, or abrasions; ■ Insect or animal bites; To Bathe or Not to Bathe? Sweat Gland Nerves Hair Follicle Blood Vessels Skin Layers Sebaceous Gland Epidermis Dermis Hypodermis Overbathing can cause skin flaking, dandruff, itchiness, and even allergic reactions. ALEXANDRA BECKSTETT ILLUSTRATION BY ROBIN PETERSON, DVM