Hypothyroidism is common in medium to large breed dogs and causes significant welfare impairment through weight gain, lethargy, and skin and coat changes that are highly responsive to treatment.
Hypothyroidism causes genuine welfare compromise: the chronic fatigue and lethargy of hypothyroid dogs profoundly reduces their ability to engage in normal activities they previously enjoyed. Weight gain compounds this by reducing exercise tolerance and increasing joint loading. Cold intolerance causes discomfort and reluctance to go outside. Skin changes including hair loss, thickening, and infection cause discomfort. The insidious onset means that dogs can suffer for extended periods before diagnosis. The dramatic response to treatment — hypothyroid dogs often becoming markedly more energetic and comfortable within weeks of starting levothyroxine — reveals the significant ongoing welfare compromise before treatment. Regular thyroid screening in predisposed breeds would reduce the duration of unrecognised suffering.