INHIBITION OF ADRENAL STEROIDOGENESIS, NEONATAL FEED RESTRICTION, ANDPITUITARY-ADRENAL AXIS RESPONSE TO SUBSEQUENT FASTING IN CHICKENS

White Plymouth Rock chickens placed under 60% feed restriction or ad l ibitum feeding, with or without metyrapone (adrenal blocking agent) tr eatment, from 4 to 6 days of age were subjected to either 8 or 24 hr f eed 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. Howev er, there was no difference in plasma corticosterone and ACTH response s between 60R and 60M chicks. Except for increases in H/L and plasma c orticosterone concentrations among ad libitum fed (AL) and 60M chicken s, respectively, there was no indication of stress response attributab le 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 tha t had been subjected to early 60% feed restriction with nonmetyrapone- treated feed. In contrast, chicks of other regimens had elevated H/L a nd plasma corticosterone responses when exposed to a similar procedure . Except for those fed ad libitum during the neonatal stage, circulati ng levels of ACTH declined following the 24-hr fast. These results dem onstrate that stress early in life without concurrent rises in circula ting corticosteroid levels may not help the biological system in copin g with subsequent stressors. (C) 1995 Academic Press, Inc.