Hypothyroidism is one of the most common hormonal disorders in dogs, causing weight gain, lethargy, and skin problems. Unlike feline hyperthyroidism, it is easily treated with daily medication that provides excellent welfare outcomes.
Hypothyroidism creates a welfare burden that is often gradual and easily mistaken for normal aging. Dogs with low thyroid function feel cold when others are comfortable, lack energy for previously enjoyed activities, gain weight despite controlled feeding, and may develop skin infections and hair loss. The lethargy is profound - affected dogs sleep more, play less, and seem fundamentally less engaged with life. Because these changes develop gradually over months, owners often fail to recognize the disease until blood testing reveals the diagnosis. The welfare case for routine thyroid screening in middle-aged and older dogs is strong because the treatment is so effective: most hypothyroid dogs transformed by thyroid supplementation within weeks is one of the most rewarding welfare interventions in companion animal medicine.