Re: Thyro L
Hi, Cindy - Primary hypothyroidism in horses is *extremely* rare. "Euthyroid sick syndrome", a term for a thyroid gland that can function normally, but due to illness or other factors is fairly common: Euthyroid sick syndrome is a condition in which serum levels of thyroid hormones are low in clinically euthyroid patients with nonthyroidal systemic illness. Diagnosis is based on excluding hypothyroidism. Treatment is directed toward the underlying illness; thyroid hormone replacement is not indicated. (from Merck https://www.merckmanuals.com/en-ca/professional/endocrine-and-metabolic-disorders/thyroid-disorders/euthyroid-sick-syndrome )
Much more commonly in our horses is just a low total T4, due to dietary, IR, or PPID issues: Horses on medications such as bute or Trimethoprim sulfa, with chronic illness such as Cushing's disease, or in racing shape may have falsely decreased total T4. (from the Cornell test interpretations for equine thyroid panels https://ahdc.vet.cornell.edu/test/list.aspx?Species=Equine&WebDisc=&TstTyp=&Test_Name=thyroid )
So, you can check thyroid levels to get a baseline, then repeat once diet etc is more under control. Get the Equine Thyroid panel if concerned: often one finds low total T4, but normal free T4 (which is available to be converted to active T3), and normal T3.
Jaini Clougher (BSc, BVSc)
Merlin (over the bridge), Maggie, Gypsy, Ranger
ECIR mod/support, BC 09
DDT+E = effective treatment for PPID and EMS/IR equines: https://bit.ly/2J4ZgYT