Focus on Health: The External Horse
The world might admit that beauty is only skin deep, but a horse's inner health is reflected onto all external features--a radiant and silken hair coat, mane, and tail mirror a horse's overall internal health.
Nutrient availability and absorption are critical to a horse's health. Stephen White, DVM, Dipl. ACVD, professor at the University of California, Davis, College of Veterinary Medicine, says, "Maintenance of normal hair cycles and turnover of epidermal skin cells takes a lot of energy, protein, and certain trace elements and minerals."
Mammals' skin is protected and stabilized in its outermost layers (the epidermis) by a process known as cornification that incorporates keratin as a structural matrix. Keratin forms as filaments from proteins to create a "waterproof" layer. Other components, such as collagen and elastin, combine with the keratin matrix to give skin its strength. These specialized epidermal cells are continuously shed and replaced.
Susan White, DVM, MS, Dipl. ACVIM, a professor at the University of Georgia's veterinary school, notes, "Normal growth of hair and keratinization of the skin use 25-30% of horses' daily protein requirements." Conditions such as gastric ulcers, sand irritation of the bowel, and internal parasitism can compromise the body's proper absorption of many nutrients.
Protein and Minerals Coat quality relies on appropriate balances of protein and minerals such as zinc, copper, iron, and selenium. "A deficiency in almost any nutrient has the potential to negatively affect the hair coat's appearance," according to Kelly Vineyard, PhD, an equine nutritionist at Land O'Lakes Purina Feed. "Protein (amino acids) and zinc are the most commonly observed deficiencies affecting skin and hair. Poor hair growth and a dull appearance result from amino acid deficiencies. Skin cells contain a moderate amount of zinc--deficiency leads to hair loss and 'parakeratosis,' (incomplete keratinization of epidermal cells) characterized by severely thickened and cracked skin."
Katie Young, PhD, also an equine nutritionist at Land O'Lakes Purina Feed, notes, "Differences in protein levels of hay versus green grass vary with plant maturity--the less mature the plant (live grass or at time of hay harvest), the higher its protein. Hindgut digestion of forage-derived protein yields few intact amino acids; an additional source of essential amino acids benefits horses maintained on a hay-only diet and/or mature grass pasture.
"While minerals are fairly stable, the higher the water content of forage, the more a horse must consume to meet daily nutrient requirements," Young adds. "Mineral interactions have significant effects and should be supplied in balanced, correct amounts."
Vitamins Fresh grass usually contains adequate vitamins for the average horse, but Young reports that shortly after harvesting, vitamins A and E leach out and aren't available in appropriate amounts. Vitamin A is important for skin health--too much or too little can lead to a scruffy hair coat. Vitamin E, in conjunction with selenium, plays an important role as an antioxidant to protect body tissues. Vitamin E deficiency also can result in a scruffy hair coat. Both vitamins A and E must be obtained from dietary sources.
Fats and Fatty Acids "Although deficiency of essential fatty acids (EFA) has never been documented in horses," says Vineyard, "owners have long recognized that adding dietary oil has positive effects on hair coat. In other species, EFA deficiency is associated with dry hair, scaly skin, and hair loss." There are two types of EFAs: omega-3 and omega-6 fatty acids, also known as polyunsaturated fatty acids.
Vineyard explains how fat improves skin and hair condition: "All cell membranes, including skin cells, contain polyunsaturated fatty acids (PUFA), so supplementation with dietary fat rich in PUFA improves membrane fluidity and integrity, giving a pleasing appearance to skin and hair."
She adds, "Hair is made up of protein, minerals, and fatty acids. As a component of skin oils (sebum), fatty acids coat each strand of hair--this oily, protective barrier gives a shiny appearance. Dietary fat also facilitates absorption of fat-soluble vitamins (including A and E), which contribute to a healthier hair coat."
Daily supplementation with at least 2 ounces of vegetable oil high in PUFA, such as corn or soybean oil, is known to improve the coat, Vineyard notes. If feeding dry fat, 7.5 ounces (3.5 cups) of rice bran or 4.5 ounces (2 cups) of ground flaxseed are equivalent to 2 ounces of oil. Horses have a high tolerance for dietary fat, but she advises that fat fed in excess of 15-20% of dry matter intake might adversely affect fecal output and digestibility of other nutrients, without further benefit to skin or hair.
Both omega-3 and omega-6 fatty acids are dietary essentials for skin and hair. Vineyard notes a diet devoid of one or the other is problematic, as is a diet too heavily enriched in either direction.
According to Vineyard, omega-6 fatty acids (e.g., corn products) have been "demonized" as contributing to immune suppression and inflammation, particularly in other species. But Vineyard says, "The best approach is to supply balanced amounts of both omega-3 and omega-6 fatty acids, but be aware that omega-3 fatty acid supplements don't have an unlimited shelf life."
She summarizes, "Allow horses fresh pasture access since green grass is an excellent source of the omega-3 fatty acid alpha-linolenic acid."
Grooming Just as brushing your hair circulates natural oils for improved luster, grooming improves the shine of a horse's hair coat. Stephen White reports, "Grooming removes dead, loose skin cells and old hairs that lose their 'sheen.' Actively growing hair has more gloss and shine."
Bathing "A cleansing shampoo removes sweat, debris, dust, and dander, doing a better cleaning job than plain water," says Stephen White. But shampoo at every bath isn't necessary, and Susan White suggests applying water with a spray nozzle to improve cleansing without shampoo. The water pressure alone can reach the hair roots and skin. She cautions, "Excessive bathing [with shampoo] removes skin oils and outer skin layers, potentially changing the composition of surface organisms with increased susceptibility to skin diseases."
There's a considerable variety of shampoo products available, but Susan White says, "Choose shampoos formulated for horses--low pH (acid) rather than high (alkaline) pH. Dilute shampoo to use only necessary amounts. Rinse thoroughly."
Stephen White favors shampoos with ethyl lactate: "It has antibacterial properties and is well-tolerated by horses ... Shampoo with benzoyl peroxide can 'bleach' or lighten coat color of dark-coated horses."
Antibacterial iodine or chlorhexidine shampoos are used sparingly to treat various skin conditions such as rain rot, but Susan White cautions, "These shampoos will dry and irritate skin if used repeatedly."
Itching (pruritus) Stephen White finds that applying cool to cold water soaks alleviates itching. Susan White describes another management approach: "Solar radiation aggravates itching regardless of cause--keep the horse out of the sun and use fans to provide relief."
Astringents, such as witch hazel or alcohol, only temporarily relieve itching, possibly through perceived "cooling," according to Stephen White, and Susan White notes these products tend to dry and harden skin, causing more pruritus. She instead recommends emollients, such as aloe vera, for dry, pruritic skin to increase water holding capacity of outer skin layers and to slow water loss.
External parasites Horses are regularly plagued by ectoparasites--flies, mosquitoes, ticks, lice, and mites. Most repellents for equine ectoparasites are permethrin-based. "These work well, but may need to be reapplied frequently," says Stephen White. "Natural" insect repellents containing citronella also require frequent application. To minimize chances of tick infestation, Susan White recommends mowing pastures to less than six inches high and removing overhanging branches where ticks perch. You can deter ticks by brushing tick powder into a horse's coat, but first test the powder in a small area on your horse's body to ensure he is not allergic before applying it to his whole body.
Woven-mesh fly sheets and leggings shield against pesky insects while blocking a portion of ultraviolet light that fades a vibrant hair coat. Susan White says, "Horses with nonpigmented skin (white markings) should be additionally protected with zinc oxide and/or stabling during peak solar radiation times (10 a.m. to 3 p.m.)."
Pastured horses might have access to photosensitizing plants that can cause photo-activated dermatitis, commonly referred to as "scratches." Nonpigmented skin is most commonly affected, with development of painful, oozing, crusty sores. Tube sock leg coverings can be useful during daylight hours (cut the feet out of tube socks and pull them up over the white leg markings). Fly face masks with lengthened nose netting partially block UV rays; ear nets protect against ear gnats and ticks.
The Outer Hoof
The hoof is another key external feature of the horse. Check feet daily for lodged stones, to remove mud and manure from frog clefts, and to monitor changes in shoes, frogs, or the white line (if unshod).
"Each section of the hoof (horn, sole, frog) is supplied by its own corium (deep inner layer beneath the epidermis)," says Steve O'Grady, DVM, MRCVS, owner of Northern Virginia Equine in Marshall. "The corium produces and replenishes these structures, dependent on its rich blood supply. Circulation is affected by overloading and compression, therefore the corium's function is influenced by many factors--the integrity of all hoof structures, foot conformation, and farriery practices."
Hooves subjected to continuous wet periods often develop problems. Hoof oversaturation occurs in inclement climates, but it also arises in persistently damp stalls and from constant bathing. O'Grady explains, "Consider a water-submerged board--as water penetrates, the board softens and falls apart."
This analogy extends to saturated hooves, as horn tubules swell with water, increasing in flexibility and losing strength and shock absorption capabilities. O'Grady suggests, "Bring horses into a dry area for several days and bed with wood products (shavings or sawdust) to allow feet to dry.
Instead of bathing with a hose, O'Grady recommends sponge baths to minimize water immersion of the hooves. Applying petroleum jelly to hooves before bathing also protects against water saturation.
O'Grady finds little value in hoof dressings: "Most hoof wall moisture is derived from inner structures in close proximity to blood circulation. In contrast, horn tubules of the outer hoof wall are extremely dense and impermeable--most hoof dressings either wear off quickly or if applied in excess, accumulate as sludge on the outer wall."
Rather than moisturizing, such sludge can trap microorganisms and create infection, particularly in the sole area, which is the most permeable area of the hoof. O'Grady likes one cosmetic dressing to use on hoof walls: "One part pine tar mixed with three parts cod liver oil doesn't accumulate when applied, yet leaves the hoof with a nice, smooth appearance.
O'Grady urges an approach that eliminates primary causes of thrush and white line disease, such as poor hygiene, moist environments, and farrier practices that degrade hoof integrity, remarking, "Good management often eliminates the need for treatment in the first place."
"Total nutritional status affects skin, hair, mane, and tail growth as well as hoof growth and integrity, but genetics and management also have considerable effects," says Young. For best results, collaborate with your veterinarian for each horse's nutritional needs. Susan White points out that regular grooming keeps skin and hair supple and lustrous and allows for regular inspection for injuries, external parasites, or skin disease. For optimal hoof strength, O'Grady summarizes, "Appropriate farriery applied to the horse's foot always improves external hoof health."
About the Author
Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.