Piglet plasma insulin (I), cortisol (C), triiodothyronine (T3) and tetraiodothyronine (T4) levels have been studied for their dynamics depending on the age and metabolic energy in ration of pregnant sows. The considerable changes occur in the concentration of adaptive hormones in the piglet blood during 24 hours after birth. The level of insulin in the piglet blood during the first day increases from 1.1 +/- 0.18 to 27.4 +/- 5.9 mkU/ml, whereas C, T3, T4 levels sharply decrease. There are no considerable differences in hormone concentration in the blood of older (5- and 21-day) piglets. It is established that insulin concentration in the blood of piglets increases 11, 7 and 2 times by the 0, 6, 12th hours, respectively, after feeding pregnant sows with the ration containing nutrient animal fat. The 3- and 2-fold increase of T3 and T4 levels, respectively, was observed in the blood of newborn piglets from sows which received high fat ration. The influence of metabolic energy in the ration of pregnant sows at the level of T3 and T4 in the piglet blood also takes place at the later stages of neonatal development. It is supposed that piglets, whose mothers received extracaloric rations are more viable because of the changes in hormonal status in the neonatal period.