Alopecia or hair loss in horses can occur for several different reasons and may be temporary or permanent. [1] Alopecia refers to the partial or complete absence of hair that occurs in any area of the body where hair is normally present. [1][2]

Congenital alopecia is a condition that is present at the time of birth. [2] This form of alopecia is non-inflammatory and may occur due to genetic factors, resulting in damage to the hair follicles. [1][2]

Acquired alopecia refers to a partial or complete loss of hair that occurs at any stage of life. [2] It is the most common form of hair loss that affects horses. [2]

Successful treatment of hair loss requires identifying and addressing the underlying cause of the condition. [1] Diagnostic dermatology and blood tests can aid in the diagnosis of acquired alopecia.

Strategies to help prevent hair loss include evaluating your horse’s skin and hair regularly, providing balanced nutrition, and treating injuries and wounds promptly.

Hair Loss in Horses

Alopecia is known to occur in various species, including humans, horses, dogs, cats, cattle, and mice. [1] The condition describes the partial or complete lack of hair in areas where it is normally present. [1]

Types of Alopecia

Depending on the cause of the condition, alopecia is classified as congenital or acquired.

Congenital Alopecia

This form of alopecia is present at birth and occurs because of damage to the hair follicles that may be associated with genetic factors. [2]

Congenital alopecia may or may not be hereditary and does not occur in conjunction with signs of clinical inflammation. There is no treatment for congenital alopecia. [2]

Acquired Alopecia

More common in horses than congenital alopecia, acquired alopecia is not present at birth but can occur at any stage of life. [2] This form of alopecia is classified as either non-inflammatory or inflammatory.[2]

Horses with acquired alopecia are born with normal hair and healthy hair follicles that can produce normal hair. [2] However, acquired alopecia results in the loss of hair due to internal or external factors.

Non-inflammatory causes of acquired alopecia in horses include autoimmune disease, stress factors such as illness, seasonal changes, rubs due to poorly fitted blankets or equipment, nutritional deficiencies, and low thyroid hormones. [2]

Inflammatory causes of acquired alopecia include infections affecting the skin or hair follicles, trauma to the skin and hair follicles, such as burns, allergic skin reactions, and skin cancer. [2]

Mad About Horses
Join Dr. Chris Mortensen, PhD on an exciting adventure into the story of the horse and learn how we can make the world a better place for all equines.
Apple Podcasts Spotify Youtube
Mad Barn Equine Nutrition Consultants

Prevalence

The exact number of horses affected by alopecia is unknown.

A retrospective study by researchers at UC Davis determined the prevalence of alopecia areata in various equine breeds was 0.017%. [3]

This study found that Appaloosas and Quarter Horse breeds were most commonly affected by the condition. [3]

Areas on the body where hair loss was most likely to occur included the mane, tail, and face of the horses. [3] The median age of affected horses was nine years, and the condition affected horses ranged from 3 to 15 years.

More than half of the horses presenting with alopecia had other medical conditions. [3] Five of seven (71.4%) owners reported a seasonal occurrence of alopecia in their horses and a worsening of the condition in the spring and summer. [3]

Clinical Signs

The clinical signs of alopecia depend on the type of and underlying cause of the condition.

Signs of congenital alopecia typically include: [2]

  • Symmetric hair loss
  • Hair loss that is localized to one area of the body
  • Well-demarcated areas of hair loss

Signs of acquired alopecia may include: [4]

  • Variation in patterns of hair loss depending on the underlying cause of the condition
  • Hair loss that is diffuse or localized to one area
  • Hair loss that is symmetric or asymmetric
  • Hyperpigmentation of hairs
  • Swelling, scaling, shedding, itching (pruritus), and thickened skin (lichenification) if inflammation is present
  • Secondary skin diseases such as bacterial infections
  • Secondary skin conditions including oily secretions of the sebaceous glands (seborrhea)

Causes

Congenital Alopecia

Congenital alopecia is rare in horses. The condition may or may not be hereditary. It results from abnormalities in the development and or function of hair follicles such as: [1][5]

  • Reduced quality and quantity of hair follicles, including follicles that do not develop completely (hair follicle aplasia) or develop abnormally (hair follicle dysplasia)
  • Reduced quality and quantity of hair fibers produced by the hair follicles

There is only one scientifically documented case of congenital alopecia occurring in a horse that was born with partial alopecia. By the time the blue roan Percheron was one year of age, the condition had progressed to become body-wide alopecia. [6]

Studies in humans and other animals suggest congenital alopecia is a complex trait involving many genes. [16]

Acquired Alopecia Associated with Inflammation

When acquired alopecia involves inflammation, inflammatory cells are present in the area where hair loss is occurring. Inflammation may result from: [1]

  • Bacterial infection
  • Fungal infection (such as ringworm infection known as dermatophytosis) [2][7]
  • Parasitic infection (associated with organisms such as ticks, fleas, demodex mites, or roundworms known as onchocercia)
  • Trauma to the skin (such as burns and injury)
  • Allergies (skin irritation, allergic reaction to specific foods, insect hypersensitivity)
  • Cancer [2][8]
  • Severe diseases involving skin infection and inflammation (cellulitis)
  • Infection of the hair follicles (folliculitis)

The above-mentioned conditions may lead to hair loss on their own but may involve itching (pruritis) that further contributes to hair loss. [1][9] Pruritis can cause affected horses to rub irritated and or painful areas of skin, thus promoting hair loss. [1]

Acquired Alopecia that is Non-Inflammatory

Acquired alopecia that is non-inflammatory (no clinical signs of inflammation) is caused by factors that slow or inhibit the growth of hair follicles, such as: [1][2][10]

  • Nutritional deficiencies (particularly protein)
  • Hormonal imbalances (such as low thyroid hormones or high estrogen level)
  • Pregnancy or lactation
  • Illness and fever
  • Autoimmune disease (alopecia areata, which involves diffuse hair loss, and linear alopecia which involves vertically linear areas of hair loss are conditions in which the immune system attacks the hair follicles.)
  • Changes in season (reported cases of seasonal alopecia that occur in the spring and summer)
  • Poisoning from mercury, thallium, and iodine
  • Friction due to poorly fitting blankets or equipment
  • Trauma to hair shafts due to excessive grooming, prolonged exposure to UV light, or exposure to chemical trauma from shampoos, pesticides, alcohol, and solvents
  • Stressors such as high fever, severe illness, pregnancy, surgery, anesthesia, and metabolic disease

Anagen effluvium refers to the abnormal diffuse loss of hair during the growth phase of the hair cycle.

Telogen effluvium refers to the abnormal diffuse hair loss during the resting phase of the hair cycle.

Diffuse hair loss is commonly due to telogen or anagen effluvium that is non-scarring and not associated with inflammation. Anagen effluvium and telogen effluvium are caused by an event such as (fever, metabolic disea