The most dogs, cats, small animals and horses shed to some extent. The reason for shedding can be the diet, animal’s breed, age, hormonal status or the grooming routine of the pet owner. This article is meant to introduce you to the different factors influencing the hair shedding cycle of animals. We separated three groups in total relating to the environment, the animal and the pet owner.
Shedding seems to be connected to seasonal temperature, but it is actually governed by day length.
Since shedding is strongly related to changes in the duration and intensity of day light, indoor animals shed more or less during the whole year. Inside living animals need to be groomed during heavier shedding periods to help remove the loose undercoat.
Outside living animals usually shed heavily as days lengthen in spring. Outdoor animals help themselves to get rid of the itching loose hair by brushing themselves.
Hair loss due to poor nutrition often involves the whole animal, but may be most obvious over the back and hips where hair follicles have shorter growth cycles and longer inactive periods. As protein is necessary for proper kertanization of the skin, hair of animals deficient in protein will become dry, dull, brittle and will shed easily and may be slow to grow.
An improper diet can cause unnatural shedding. B vitamins are important for proper hair growth. Copper is important for hair production and a deficiency will result in a poor hair coat. Zinc can also influence hair growth in dogs.
The breed of dog affects how much the animal will shed.
Some breeds tend to be low shedding because almost all of their follicles are in the growing phase almost all the time; their hair continues to grow. Some have most of their follicles in the shedding phase and may be almost completely hairless.
Dogs with a long hair growth cycle will shed less.
Dogs with long, fine hair tend to shed less than other breeds. Some breeds shed very little hair. Strictly "non-shedding breeds" do not exist. However, most breeds with single coats are considered "non-shedding" because their shedding is not very noticeable. Short-haired dogs shed the most often and continuously.
Breeds with a high density of hair follicles have more guard hairs (topcoat) per square inch and less undercoat. They shed less than breeds with a low density of hair follicles but more undercoat associated with each one. These breeds blow their coats with every season change, losing tufts of undercoat at a time.
In general, no new hair follicles are formed after birth. Initially, a puppy or kitten has simple hair follicles that hold a single hair. The secondary hairs emerge at about the age of 12 weeks. The coat becomes more dense, stiffer and coarser depending on the characteristics of the breed. Puppies or kittens do not actually "lose" their first coat, rather they gain an adult coat. The age of the first shed depends on the season of birth and occurs between 4 and 14 months.
Blood carries hormones that determine the hair growth phases. Shedding is controlled by hormonal changes that are tied to day length. Some hormones will stimulate hair growth, while others will delay it.
Female animals tend to shed after a heat cycle and after giving birth. This shedding typically occurs when the litter is five to twelve weeks old. False pregnancy and nervous lactation can cause loss of hair from the chest, belly and sides.
Hair follicles and skin cells are also strongly influenced by thyroxin. Thyroxin initiates hair growth and increases the rate of new growth. A deficiency in thyroid hormone (hypothyroidism) results in poor hair growth and thinning of the hair, especially over the back.
Corticosteroids delay hair growth by inhibiting new hair growth resulting in thinning of the hair as well. A lack of growth hormone results in retention of the hair in young animals and lack of hair growth in adults.
Some animals' hair changes color with the season. This occurrence is another hormonally-controlled aspect of the hair cycle. The activity of melanocytes changes to give hair more or less pigment.
Anytime an animal is stressed, the skin and coat suffer. All stressors, noise, boredom, fear, sudden changes to environment, inconsistencies in food or water supply, a lack of visual contact, pain and anxiety accentuate hair loss. During the initial phase of stress, such as a visit to the vet or groomer, stress hormones are released into the bloodstream inducing shedding for a couple of days. In cases of daily stress, shedding becomes even more problematic.
Intensity and speed of shedding varies with different species, breeds and individuals, but stressful conditions typically cause hair to shed first on the body and rear hips.
Bathing too frequently can dry out the hair coat and cause excessive shedding. Attention should be paid to the products used, as skin pH differs between species. Choice of shampoo should be strictly related to skin pH.
Some dogs may have a pause in hair growth after clipping. After several months of a lack in re-growth of hair, this resolves spontaneously.