Neonatal levels of plasma thyroxine in male and female calves fed a colostrum or immunoglobulin diet or fasted for the first 28 hours of life.

The effect of diet on changes in plasma thyroxine levels was studied in 83 newborn Friesian X Holstein calves. Fifty-four received four copious meals of first-milking colostrum at 4, 10, 16 and 22 neonatal hours. At the same time, 24 animals received four meals of a solution of colostrum immunoglobulins containing little energy, and 5 calves were kept fasted. The last two treatments resulted in lower plasma thyroxine levels than those in colostrum-fed calves. At the same time, plasma thyroxine level was higher in females than in males during the first neonatal week.