Overview
The skin (cutis) covers the whole surface of the body and is continuous with the mucous membranes at the natural openings. It acts as a physical, chemical and microbiological barrier and takes part in thermoregulation and in the perception of touch, temperature, pain and itch. In the horse it is relatively thin and very sensitive; beneath it, the cutaneous trunci muscle lets the animal twitch the skin to drive off insects.
Layers
- Epidermis: keratinised stratified squamous epithelium without vessels; it thickens on the nostrils, lips and the skin of the distal limbs.
- Dermis: dense connective tissue with collagen and elastic fibres; it holds vessels, nerves, hair follicles, arrector pili muscles and glands.
- Hypodermis (tela subcutanea): loose connective tissue with fat; almost absent on the distal limbs, where the skin lies directly on tendons and bone.
Hair and glands
- Coat: simple follicles, one hair per opening. The winter coat is long and dense and is shed in spring.
- Long hairs: thick, long hairs of the mane on the neck, the forelock on the forehead and the tail. Draught horses also have tufts of feather on the palmar and plantar fetlocks.
- Tactile hairs: long and stiff, around the nostrils, lips and eyes.
- Sweat glands: apocrine and very abundant. The horse is one of the few domestic animals that loses most of its heat by sweating. Its sweat contains a protein, latherin, which makes it foamy and helps it wet the coat.
- Sebaceous glands: open into the follicles and lubricate hair and skin.
Special structures
- Chestnuts (castanea): horny plates on the medial forearm, proximal to the carpus, and on the medial tarsus.
- Ergots (calcar metacarpeum and metatarseum): small horny projections on the palmar or plantar side of the fetlock.
- Hoof: a modified skin structure described separately.
Clinical relevance
- Equine sarcoid: the most common skin tumour of the horse, associated with bovine papillomavirus types 1 and 2; locally aggressive and often recurs after removal.
- Melanoma: very common in older grey horses, at the tail base, perineum and parotid region.
- Insect bite hypersensitivity (sweet itch): hypersensitivity to biting midges (Culicoides), with intense itching of the mane and tail base.
- Dermatophilosis and pastern dermatitis: crusts and exudate on the back after prolonged rain, or on the distal limbs in wet, muddy conditions.
- Dermatophytosis (ringworm): caused by Trichophyton equinum and Microsporum; circular areas of hair loss, often in the girth and saddle area. It is contagious and can spread to people.
- Anhidrosis: loss of the ability to sweat in hot, humid climates, with a risk of heat stroke.