In dogs, the thyroid is a gland in the neck that produces hormones to help regulate metabolism and other bodily functions. Hypothyroidism, in which the thyroid does not produce enough hormone, is much more common in dogs than hyperthyroidism, in which the gland produces too much hormone. Either condition can lead to a range of problems that produce various signs and symptoms.
Weight and Activity Level Changes
Because thyroid hormone plays a role in regulating metabolism, if there is too little of it present in your dog's system, it may appear sluggish and sleep a lot. Pet Place says lethargy is present in 70 per cent of dogs with an underactive thyroid. Your dog may also gain weight because of its impaired metabolism and lack of activity. The lack of thyroid hormone may also lead to a slower-than-normal heart rate. In hyperthyroidism, many of the symptoms are reversed. For instance, your dog may have a hard time maintaining its weight even though its appetite may increase. It may also have an increased amount of energy and increased heart rate, and it may appear nervous or jittery.
Hair and Skin Problems
Hormones produced in the thyroid help regulate skin and hair growth, so when there is a deficiency, it can lead to problems. These include excessive shedding, slow growth, hair loss and hyperpigmentation of the skin. According to Pet Place, hair loss and excessive shedding occur about 60 to 65 per cent of the time in dogs with hypothyroidism, while skin pigmentation problems are present about 25 per cent of the time.
Intolerance to Cold
The slowing of metabolism can also lead to an inability for dogs with hypothyroidism to regulate their body temperature properly. This manifests most often as intolerance to cold. Pet Place reports that cold intolerance occurs in 15 per cent of dogs with hypothyroidism. This symptom may not be readily apparent, but the Merck Veterinary Manual says dogs with this problem will often seek out warm places.
There are other common symptoms of both hypothyroidims and hyperthyroidism. These include anaemia and high cholesterol, which occur in half or more of dogs with hypothyroidism, according to Pet Place. Dogs with hyperthyroidism may exhibit the additional symptom of excessive thirst and may urinate more frequently as a result.