What Are the Causes of Low T4 Hormone in Dogs?

If your dog is overweight or inactive, he may have low levels of the hormone T4, which can indicate hypothyroidism. In dogs, hypothyroidism is the most common hormone-related disease; like a human thyroid disorder, the problem is usually preventable. Fortunately, there are medications to raise a dog's T4 level, which can treat the disorder.

  1. Canine Hypothyroidism

    • Like the human thyroid gland, a dog's thyroid gland is attached to the throat's windpipe and produces both T3 and T4 hormones. The thyroid's T3 hormones are active, while T4 hormones are inactive forms of T3 that move from the thyroid gland into the bloodstream. A dog's pituitary gland, which resides in the base of the brain, controls T4 production. If there is a deficiency in a dog's T4 production levels, hypothyroidism may be present.

    Common Factors

    • There are four causes of low T4 hormone production in humans, including congenital disease, a dietary deficiency of iodine, immune-related damage to the thyroid gland or a natural slowing down of the thyroid gland. In dogs, two of these causes account for low T4: immune destruction of the thyroid and natural deterioration of the thyroid. Dogs usually show signs of poor T4 hormone production in mid- or late life. Certain dog breeds are more susceptible to low levels of T4 hormone, including golden retrievers, Great Danes, Irish setters, dachshunds, boxers and Doberman pinschers.

    Physical Traits

    • Dogs with low levels of T4 hormone often have a facial disorder known as tragic face, which presents as a thickening of face and head tissue and multiple skin folds. The thickening of the skin tissue may also develop on other areas of the dog. Other common physical characteristics include skin abnormalities or infections, hair loss, dry or brittle coats, lethargy, anemia (lack of iron) and obesity. Dogs with low T4 levels are also prone to high cholesterol levels.

    Treatment

    • Treatment for low T4 hormone production in dogs is available, but medication is a lifetime endeavor. Veterinarians prescribe two oral doses of T4 a day to start; as the condition improves, the dose may be reduced to one pill a day. The price of medication varies by the manufacturer, but pills are affordable for most dog owners. Once treatment begins, the veterinarian monitors the dog's hormone levels regularly to check on progress.