Hypothyroidism:

Hypothyroidism is a condition which is characterized by low levels of thyroid hormone.
Since thyroid hormone is involved in the control of cellular metabolic rate and signaling of changes in cellular requirements, the effected dog has poor overall health.

Hypothyroidism occurs with equal frequency in males and females.

The average age of onset is 3 years.
Early symptoms of hypothyroidism include low energy levels, susceptibility to infection and elevated cholesterol levels.
As time progresses, the dog will manifest signs of obesity, weakness, inability to participate in active exercise, intolerance to cold, poor coat and hair loss, infertility and skin disease.

The course of hypothyroidism occurs over several years and because of its typically slow onset and subtle signs, owners often do not recognize their dogs have a problem.

If your dog shows signs that may indicate a thyroid problem ask your vet to test.