The thyroid gland is located either side of around a dog’s larynx and its function is to produce a hormone called thyroxine, which regulates the metabolism rate of most tissues in the body. A thyroxine deficiency due to an affected thyroid gland causes cell function to decrease, impacting on several of the body’s organ systems. Hypothyroidism affects approximately 0.2% of all dogs. Signs develop gradually and spread widely.

Lethargy, depression, getting tired easily from exercise, sleeping a lot more than usual, changes in behaviour or disposition, gaining weight despite no other changes to lifestyle or diet, seeking warmth frequently. Several skin issues can occur ranging from hair loss, dry coat, poor skin healing and increased occurrence of bacterial skin and ear infections. Several complications can arise if the hypothyroidism is not treated. The heart will beat more slowly, becoming weaker over time. The nervous and muscular system can also be affected, leading to paralysis, poor reflexes and general weakness. Regurgitation (passive vomiting) after meals can also occur, when food can't pass properly into the stomach due to muscle weakness in the oesophagus.

Causes of hypothyroidism can range from having insufficient iodine in the diet, to cancer, or even an infection. In 90% of dogs, the cause is undetermined. Fortunately, the condition is easily managed with hormone supplementation, and the outcome is usually excellent. Dogs can live a full and healthy life as long as they receive their hormone supplementation for the rest of their lives, with the dosage as directed by their veterinarian.