Hypothyroidism is one of the most common endocrine disorders in dogs, causing progressive metabolic slowing that impairs physical and mental wellbeing, but responds well to straightforward and affordable daily hormone replacement.
Hypothyroidism causes a progressive metabolic slowdown that owners often mistake for normal ageing. Affected dogs become lethargic, gain weight despite unchanged diet, seek warmth, and lose interest in exercise and play. The coat becomes dry, brittle, and thin. Mental dullness and reduced responsiveness may be interpreted by owners as cognitive decline. The welfare impact is substantial because the condition develops gradually, meaning dogs may live with significant metabolic impairment for months or years before diagnosis. Treatment is transformative — most dogs regain normal energy, body weight, and coat within weeks of starting levothyroxine. Regular monitoring of thyroid levels allows dose adjustment to maintain optimal welfare outcomes throughout the dog's life.