Hypothyroidism — underactive thyroid gland — is the most common endocrine disorder in dogs and causes a constellation of symptoms that significantly impair quality of life yet are frequently attributed to normal ageing.
Hypothyroid dog welfare is chronically impaired by a condition that is entirely treatable yet frequently missed because its signs are gradual and mimic normal ageing. A dog that gains weight steadily, becomes less willing to exercise, seeks warmth, and loses coat lustre over months is showing clear hypothyroid signs that owners commonly attribute to "getting older." The welfare cost of untreated hypothyroidism includes reduced energy and motivation for activity, discomfort from weight gain and skin changes, and potentially impaired mental function (myxedema coma in severe cases). The transformation following appropriate levothyroxine treatment is often dramatic — owners report that their dog seems "years younger," with restored enthusiasm for walks, play, and social interaction. This before-after contrast confirms the substantial welfare deficit that existed before diagnosis. Annual thyroid screening in predisposed breeds from middle age could prevent years of subclinical hypothyroid welfare impairment.