Hyperthyroidism is the most common endocrine disorder of older cats, causing significant welfare harm that is highly treatable when detected early through regular veterinary screening.
Feline hyperthyroidism creates a welfare paradox: the early symptoms — increased appetite and apparent energy — may look like improvement to owners, while the cat is in fact experiencing a metabolic state that causes significant physiological distress and progressive organ damage. Weight loss despite voracious appetite, muscle weakness, and cardiovascular stress all reduce quality of life. Without treatment, progressive cardiac hypertrophy leads to heart failure and significantly shortened lifespan. The welfare case for early detection is compelling: annual T4 testing in senior cats costs little and identifies disease before significant welfare harm has occurred. Treatment — particularly radioiodine therapy — is highly effective, restoring normal thyroid function and dramatically improving welfare and longevity. Owner education about the importance of senior cat screening is the primary gap to address.