Inhibition of adrenal steroidogenesis, neonatal feed restriction, and pituitary-adrenal axis response to subsequent fasting in chickens.

White Plymouth Rock chickens placed under 60% feed restriction or ad libitum feeding, with or without metyrapone (adrenal blocking agent) treatment, from 4 to 6 days of age were subjected to either 8 or 24 hr feed deprivation at 36 days of age. Chicks subjected to the neonatal 60% feed restriction (60R) but not those provided metyrapone during the procedure (60M) had elevated heterophil/lymphocyte (H/L) ratios. However, there was no difference in plasma corticosterone and ACTH responses between 60R and 60M chicks. Except for increases in H/L and plasma corticosterone concentrations among ad libitum fed (AL) and 60M chickens, respectively, there was no indication of stress response attributable to the subsequent 8 hr fast. Feed withdrawal for 24 h did not cause rises in H/L ratios and plasma levels of corticosterone of chicks that had been subjected to early 60% feed restriction with nonmetyrapone-treated feed. In contrast, chicks of other regimens had elevated H/L and plasma corticosterone responses when exposed to a similar procedure. Except for those fed ad libitum during the neonatal stage, circulating levels of ACTH declined following the 24-hr fast. These results demonstrate that stress early in life without concurrent rises in circulating corticosteroid levels may not help the biological system in coping with subsequent stressors.