Hypothyroidism is the most common endocrine disorder in dogs, causing weight gain, lethargy, skin changes, and reduced quality of life. Early diagnosis and lifelong treatment restore welfare significantly.
Hypothyroid dogs experience significant welfare impact before diagnosis: lethargy reduces enjoyment of exercise and play; weight gain strains joints and reduces mobility; skin changes including seborrhoea and bacterial pyoderma cause itching and discomfort; peripheral neuropathy in advanced cases causes weakness and pain. Dogs may be labelled "lazy" when in fact they are suffering from a manageable condition. Once diagnosed and treated with oral levothyroxine, the welfare improvement is dramatic — most dogs become active, lose weight, and show return of coat quality within weeks. Lifelong medication is required and monitoring of thyroid levels every 6–12 months ensures dose remains appropriate. The condition is not heritable in all cases but immune-mediated forms have a genetic component — breed-health committees should monitor prevalence in affected breeds.