Hypothyroidism is the most common endocrine disorder of dogs, causing weight gain, lethargy, and skin problems that significantly reduce quality of life without treatment.
Hypothyroidism causes chronic, progressive welfare compromise that owners often attribute to normal ageing. Weight gain despite unchanged feeding causes owner frustration and may lead to inappropriate dietary restriction; lethargy reduces engagement in activities dogs enjoy; cold intolerance causes discomfort in cooler environments; skin and coat changes cause pruritus. Dogs with untreated hypothyroidism may also show behavioural changes including aggression or fearfulness linked to the neurological effects of thyroid hormone deficiency. Treatment response is typically dramatic and rewarding for owners — affected dogs regain energy, lose weight appropriately, and show coat improvement within weeks. Regular monitoring of thyroid levels after dose stabilisation ensures continued welfare benefit.