Hormonal status and regulation of glycemia in neonatal calves during the first hours of postnatal life

The aim of this study was to examine changes in some hormones concentrations in calves during the first 32 hours of neonatal life and to estimate their association with glycemia. Thyrty two Holstein breed calves were selected for the study. Blood samples were taken at 30, 60 and 90 minutes postnatal. Calves received pooled colostrum: primary colostum (1.5 L, 2 hours after birth), secondary colostrum (2 L, 14 hours after birth) and tertiary colostrum (2 L, 26 hours after birth). Blood samples were taken at hours 5, 20 and 32 of neonatal life. Concentrations of glucose, insulin, cortisol, thyroid hormones and IGF-I and abundance of IGFBP-1, IGFBP-2 and IGFBP-3 were determined in the blood serum. The T3/T4 ratio was also calculated. Calves were born hypoglycemic (glycemia was 2.56 +/- 1.05 mmol/L at birth). Thereafter, glycemia significantly increased (p is less than 0.001) to 3.05 +/- 0.89 mmol/L at min 90. Glucose concentration showed a further increase after colostrum intake and was significantly higher than at the initial value in all examined periods (p is less than 0.001). During the first 90 minutes of neonatal life insulinemia decreased significantly (p is less than 0.001) compared to initial value (26.33 +/- 10.05 microlU/l) and it measured 18.66 +/- 5.56 microlU/l at min 90. Cortisolemia was highest at minute 30 (85.08 +/- 19.36 nmol/L) and than decreased until the end of the experiment (p id less than 0.001) compared to initial values in samples obtained during the period of colostrum intake. A significantly high correlation was determined between glycemia and cortisolemia in all examined periods before the first colostrums intake (r2=0.854; p is less than 0.01 at min 30; r2=0.742; p is less than 0.01 at min 60 and r2=0.551; p is less than 0.01 at min 90). T4 concentrations significantly increased during the first 2 hours, while T3 concentrations decreased, significantly from min 30 to min 90 postnatal (p is less than 0.05). T3/T4 ratio significantly increased during the first 2 hours of neonatal life. After first colostrum intake, concentrations of both hormones rose significantly compared to the initial level, but T3/T4 ratio did not change and maintained the value determined at minute 90. IGF- 1 concentrations significantly decreased during the first 2 postnatal hours. A significant positive correlation was observed between IGF-1 concentration and insulinemia (r2=0.463; p is less than 0.05 at min 30, r2=0.662;p is less than 0.01 at min 60 and r2=0.583; p is less than 0.01 at min 90). IGFBP-3 abundance significantly decreased, while IGFBP-1 significantly increased in this period. IGFBP-2 abundance was highest at birth. Results presented in this study indicate that the increase in glucose concentration during the first 2 hours of neonatal life, before the first colostrum intake is mainly the result of increased activity of the adrenal cortex in cortisol secretion and extrathyroidal tissue thus providing sufficient triiodothyronine. Immaturity of mechanisms responsible for insulin secretion provides the dominance of catabolic processes. Changes of the IGF system provide a rise of glucose concentration and establishment of energy balance.