Changes in serum thyroid hormone levels in newborn calves as a diagnostic index of endemic goiter

Maximum serum thyroxine (T-4) and triiodothyronine (T-3) levels of healthy calves were seen at 1 day after birth, and thereafter rapidly decreased unt il 5 days after birth. They stabilized until 2 weeks after birth, then grad ually decreased until 4 weeks after birth. Serum T-4 levels of calves with endemic goiter tended to be lower than those of healthy ones, but showed si milar levels to those of adult cows. T-3 levels of calves with goiter were similar to those of healthy ones, but showed higher variation. T-4/T-3 rati o of calves with goiter were significantly lower than those of healthy ones and adult cows. While individual levels of serum T-4 and T-3 at just after birth could not be considered as a diagnostic index, the T-4/T-3 ratio cou ld be adopted as a diagnostic index of endemic goiter.