FACTORS WHICH AFFECT SERUM T(3) AND T(4) LEVELS IN THE HORSE

When evaluating resting thyroid hormone levels, practitioners should consider: time of day when sampling is performed, climate, diet, concurrent disease, age of horse, stage of estrus cycle, and level of training. Before thyroid hormone levels are evaluated a practitioner must first rule out any concurrent disease or prior drug administration. Dietary iodine intake should be assessed. Some supplements, particularly those containing kelp, are extremely high in iodine. If a practitioner deems a horse to truly be hypothyroid after taking into account all the factors which affect thyroid hormone secretion, a trial of therapy using replacement hormone supplementation is warranted.