Hypothyroidism is the most common hormonal disorder in dogs, causing weight gain, lethargy, skin changes, and cold intolerance that are often mistaken for normal aging, delaying diagnosis and treatment.
Hypothyroidism causes chronic, insidious welfare harm that accumulates over months before diagnosis. Affected dogs feel cold, tired, and physically uncomfortable from the metabolic slowing caused by thyroid hormone deficiency. They gain weight despite not overeating and lose the cognitive sharpness and activity that characterise their healthy selves. The tragedy of undiagnosed hypothyroidism is that these changes are frequently attributed to normal aging — leading to years of avoidable suffering. Treated hypothyroid dogs recover dramatically: the return of energy, coat quality, and engagement with life after initiating levothyroxine therapy is one of the most rewarding responses in veterinary practice. Lifelong management requires consistent twice-daily dosing and periodic monitoring, but the welfare outcome for a well-managed hypothyroid dog is excellent. Breed health programmes that reduce the incidence of lymphocytic thyroiditis through genetic testing represent an important preventive welfare measure.