You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Reptiles and Chelonia possess a thyroid gland which secretes thyroid hormone. If insufficient hormone is secreted hypothyroidism occurs

The thyroid hormones are responsible for many activities in the body including  :

• Regulating metabolism
• Activity
• Growth
• Temperament
• Skin production, health and shedding 

Hypothyroidism is reported to occur most frequently in captive herbivorous chelonia particularly giant land tortoises  but it also occurs in smaller specimens and in reptiles eg Green Iguanas.

Causes include :

• Iatrogenic - primary or secondary thyroid gland disease of unknown cause
• Iodine deficiency
• Large intake of goitrogenic vegetables - eg bok choy, Brussels sprouts, broccoli, cabbage, kale, soybean sprouts (tofu), spinach. These plants contain anionic goitrogens - glucosinolates and thiocyanates that bind iodine rendering it unavailable.

Signs of hypothyroidism include :

• Anorexia
• Apparent weight gain (may be fluid accumulation)
• Goitre - enlargement of the thyroid gland
• Lethargy
• Oedema - limbs
• Reduced growth rate

Treatment 1 - iodine deficiency can be corrected by iodine supplementation as :

• Add sodium iodide supplement to food - in bread (several times a week) - tastes unpleasant
• Add sodium iodide solution supplement to water - tastes unpleasant
• Give powdered kelp tablets (contain iodine)
• Give iodinated casein supplement
• Avoid goitrogenic foods

The dose rates that have been recommended for iodine supplementation is 2-4mg/kg by mouth every 7 days *, however authors differ in their recommendations,  and one advises that a supplement containing 6-10mg of iodine/kg of supplement should be given with every meal*

Treatment 2 - thyroid hormone replacement therapy

• Administer thyroxin (T4) orally

The dose rate of levothyroxine that has been recommended for reptiles is 20 micrograms/kg by mouth on alternate days *

* For most reptiles the pharmacokinetics of drugs and precise nutritional requirements have not been evaluated, so these are guidelines only. Also, most drugs are not licensed for use in reptiles, so care is needed.