In canines, hypothyroidism is commonly caused by autoimmune diseases that damage the thyroid gland, leading to insufficient hormone production. This condition often manifests in middle-aged dogs and can result in a range of symptoms, including weight gain, lethargy, skin issues, and a dull coat. The thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3), play a crucial role in regulating metabolism, and their deficiency can significantly impact a dog's energy levels and overall health. Managing hypothyroidism is vital for promoting longevity in dogs, as untreated cases can lead to more severe health issues over time. Regular veterinary check-ups are essential for early detection and treatment, which typically involves hormone replacement therapy. With appropriate management, many dogs with hypothyroidism can lead healthy, active lives, contributing to their overall well-being and longevity.