Hypothyroidism is one of the most common endocrine disorders in dogs, caused by underproduction of thyroid hormones and leading to a wide range of symptoms that significantly affect quality of life when undiagnosed or poorly managed.
Undiagnosed hypothyroidism causes progressive deterioration in quality of life over months to years. Affected dogs experience lethargy that limits their ability to exercise and engage in normal behaviour, weight gain that compounds metabolic effects, and skin and coat changes that may cause discomfort. The gradual onset means owners often attribute signs to normal ageing rather than a treatable condition. Once diagnosed and treated, welfare improves dramatically in the majority of cases. The main ongoing welfare concern is ensuring consistent medication administration and monitoring, as under-treatment causes return of symptoms and over-treatment causes hyperthyroid signs.