Abstract: Increased mortality during the first wk of brooding is typical in broiler offspring from young breeder hens. Therefore, the purpose of this study was to evaluate the age-dependent changes in various physiological parameters of broiler chicks from young breeder parents (29 wk of age) through the early stages of brooding (72 h), and to identify those parameters which might be most predictive of future performance. In an effort to simulate procedures in the poultry industry, chicks were subjected to a 12-h delay in brooding placement after hatch in a broiler hatchery. In association with growth through 72 h post-hatch, chick relative liver weight (RLW) and liver glycogen content (LGLY) peaked at 72 and 48 h, respectively, and chick rectal temperature (RT) was greater between 24 and 72 h compared to that at both 0 and 6 h. Furthermore, plasma refractive index (RI) was greatest at 24 h and RI at 48 h was greater than that at 6 h. At hatch (0 h), RI was negatively correlated with BW but was positively correlated with RT, and RLW at hatch was positively correlated with hematocrit (HCT) at 6 h. Also, plasma glucose (GLU) at hatch and RT at 6 h were positively correlated. Between 24 and 72 h, BW was positively correlated with RLW and RT, and was negatively correlated with HCT and RI. There was a negative correlation between HCT and RI, but HCT was positively correlated with body fat loss score (BFLS) and RI. Also, between 24 and 72 h, chick RT was negatively correlated with BFLS and RI, and LGLY and GLU were positively correlated. These data demonstrate a close association between metabolic rate and growth in these post-hatch chicks, and while they experienced increases in BW and RT through 72 h, dehydration, as indicated by increased RI at 24 h, may have retarded growth. Plasma refractive index was the only blood parameter that changed significantly over time, fluctuated oppositely to that of BW between 24 and 72 h, and increased significantly between 6 and 24 h when chicks failed to gain BW. These associated changes with time and the maintenance of consistent negative correlations between RI and BW at hatch and between 24 and 72 h post-hatch indicate that RI may be a sensitive, practical, and reliable indicator of the physiological response of a post-hatch chick to common brooding management and would, therefore, be a useful indicator of future performance.