Hypothyroidism is the most common endocrine disorder in dogs, caused by destruction of thyroid tissue. Once diagnosed, daily levothyroxine supplementation typically restores normal quality of life.
Hypothyroidism represents one of the clearest examples in veterinary medicine of a condition where diagnosis and treatment dramatically restore quality of life. Affected dogs often live for years with gradually worsening fatigue, skin problems, and weight gain before the diagnosis is made — during which time their capacity to exercise, engage with the world, and feel well is significantly reduced. Owners often normalise these changes as ageing, missing the opportunity for treatment. Once appropriately treated, most hypothyroid dogs show striking improvements in energy, coat quality, and engagement within weeks. The welfare cost of untreated or undertreated hypothyroidism is real, even if the suffering is less acute than in painful conditions.