Equine Hypothyroidism

The prevalence of equine hypothyroidism is controversial. Most believe it to be a rare condition.

TRH Stimulation Test

  1. Take a basal blood sample
  2. Inject 1 mg TRH per horse or 0.5 mg per pony i/v slowly over one minute
  3. Collect a second blood sample 4 – 6 hours later
  4. Label both samples clearly and request TT4 analysis.


In normal horses and ponies, TT4 is expected to rise at least 1.4 times basal following stimulation.
In the horse, TT3 rises earlier and more dramatically than TT4 and so its measurement may be valuable. In normal animals TT3 will rise up to 3 times the basal value after 4 – 6 hours.