Hair loss, technically called ‘alopecia’, is partial or complete lack of hair in areas where they are normally present. Alopecia doesn’t refer only to hair loss; it also includes coat defects, and failure of hair growth. –by Dr Preeti Mor and Dr Rohit Kumar

Hair loss is typically associated with an underlying medical disorder. Many medical conditions involve hair loss. Some can be a result of genetics, while other diseases can be caused due to external parasites, fungal and bacterial skin infections, certain drugs, hormonal/endocrine imbalances – Cushing’s Disease, Addison’s Disease, Hypothyroidism, Hyperthyroidism, etc. Allergies, stress, poor nutrition, lack of proper grooming, and cancer can also cause hair loss in dogs.

How does dog hair grow?
Hair begins growth within a little pocket called a follicle where it is nourished by proteins and other materials in the blood. Blood also carries hormones, such as epidermal growth factor, that determine the growing, resting, regressing, and shedding phases. Hormones that control hair growth are influenced by sunlight and temperature. Thus, many pets have major growing and shedding cycles each spring and fall. With more pets kept indoors in a controlled climate, marked growing and shedding cycles are less frequent, and they tend to shed evenly throughout the year.  The rate at which hair grows is influenced by hormones and by blood supply. A good blood supply brings nutrients and a normal concentration of hormones so that the area experiences healthy hair growth. Areas with a poor blood supply do not have healthy hair growth.

Breeds most susceptible
There is no particular age or gender predisposition for development of alopecia. Although certain breeds are at an increased risk

  •  Dachshunds have a breed predilection for thinning over the ears, abdomen, and neck.
  •  Hair loss due to hypothyroid disease affects – Afghan Hound, Airedale, Boxer, Chow Chow, Cocker Spaniel, Dachshund, Doberman Pinscher, English Bulldog, Golden Retriever, Great Dane, Irish Setter, Irish Wolfhound, Miniature and Giant Schnauzer, Newfoundland, Poodle, Scottish Deerhound, and Shetland Sheepdogs.
  •  Hair loss due to hyper-adrenocorticism (Cushing’s Disease) affects – Beagle, Boston Terrier, Boxer, Dachshund, and Poodle.
  •  Some breeds grow hair very slowly after being clipped – Siberian Huskies, Alaskan Malamutes, Chow Chows and mixed breed dogs with Northern genetics.
  •  Doberman Pinschers and many other breeds are prone to developing colour dilution alopecia.
  •  Alopecia X (also called adrenal reproductive hormone imbalance and sometimes called “Black Skin Disease”) occurs more commonly in plush-coated breeds such as Pomeranian, Chow Chow, Keeshond, and Miniature Poodle.

Causes
Parasites
External parasites are notorious for causing alopecia in dogs. Fleas, ticks, lice and mites can all cause intense itching and scratching which leads to hair loss. Mange may also cause localized to generalized hair loss with redness and mild scaling.

Fungal infections
Fungal infections of the skin (called ‘Dermatophytosis’) can cause partial to complete alopecia with scaling and redness. Some fungal infections are zoonotic, which means that they have the potential to cause skin lesions in people as well.

Bacterial infections
Bacterial skin infections can cause alopecia with redness, skin crusting, and circular patterns of hair loss. Bacterial folliculitis is the most common cause of multifocal alopecia in dogs.

Allergies
Allergic pets have itchy skin, and in response they scratch or chew out their hair. Pets can be allergic to:

  •  Foods – Grains (wheat, corn, soy), meat, fish, pork, milk, yeast.
  •  Inhaled allergens – Pollen, cigarette smoke, perfumes
  •  Contact allergies – Walking through grass, chemically treated floors or carpets

Poor nutrition
Hair requires a constant supply of nutrients to remain anchored in the skin. Nutrients that support healthy hair are same as those that support healthy skin: vitamins, minerals, antioxidants, and Omega 3 and Omega 6 fatty acids. When the body doesn’t receive a balanced supply of nutrients hair becomes dull, loosens, and falls out.
For example, pets on diets have thin, dull coats. Some Northern dog breeds, such as the Siberian Husky, have a genetic tendency of zinc deficiency that leads to skin and coat problems. The problem is in the pet’s inability to absorb zinc, which is usually present in adequate amounts in the diet. The medical term is Alopecia X of the Northern breeds.

Blood flow
Hair is a living element anchored in the follicle and is nourished by blood for most of its cycle. If blood circulation is poor, hair will not grow well. Pets with weak hearts, low blood pressure, and chronic anaemia may have dull coat and skin.

Excessive or deficient hormone levels
Many hormones influence hair growth, including testosterone, estrogen, melatonin, growth hormone, thyroxin, and cortisol. Abnormal levels of these hormones cause hair to be too thin or to be too thick.

  •  Thyroxin increases the rate at which cells grow and multiply because it stimulates the cell’s nuclear machinery. Hair follicles and skin cells are as strongly influenced by thyroxin. With normal thyroxin levels, hair growth is normal. With insufficient thyroxin, which usually occurs in dogs with hypothyroidism, hair growth is slow and they have thin hair especially over the back.
  •  Cortisol is a hormone released from the adrenals that is carried by the blood. Cortisol level can be excessively high due to Cushing’s Disease or cortisol medication overload. This may lead to hair thinning over the back all the way down the tail, leaving tuft of hairs at the very end (rat tail). If hair is clipped anywhere on the body, it grows back very slowly.

(….to be continued in next issue)

(Dr Preeti Mor, PhD in Animal Nutrition and Dr Rohit Kumar, MVSc, Animal Nutrition are from National Dairy Research Institute (NDRI), Karnal, Haryana)