The influence of dietary iodine on iodine in the blood serum of cows and calves in the perinatal period.

Concentrations of total iodine (TI) and protein-bound iodine (PBI) in the blood serum of both cows and their neonatal calves were related to the iodine content of the diet fed to the cows. A group of six cows (group 1) fed a diet containing 0.6 ppm iodine had mean concentrations of TI and PBI of 4.1 and 3.4 microgram/100 ml respectively. A second group (group 2), fed a diet containing 4.6 ppm iodine, had concentrations of 33.8 and 7.6 microgram/100 ml of TI and PBI respectively. Calves of groups 1 and 2 had mean concentrations of TI of 21 microgram/100 ml and 96 microgram/100 ml respectively within 24 h of birth, but these concentrations declined markedly over a period of eight days. Evidence was obtained that the high concentrations of TI, and also of PBI, in neonatal calves relative to the concentrations in their dams resulted mainly from placental transfer rather than from the ingestion of colostrum.