Small (48-54 g) and large (58-64 g) or low (≤1.070) and high specific gravity (≥1.080) eggs from broiler breeder flocks were used. The hatching sequence was divided into four periods with 25% of the chicks being hatched in each period. One-half of each group was weighed and returned to the hatcher and the remainder were placed in floor pens. Hatch-held chicks were removed at 21 days, l2 hrs, weighed and placed in floor pens. Effect of two post-hatch holding times (0 and 30 hrs) on bursa and spleen weights were measured through 35 days of age. Hematocrits, heterophil/lymphocyte ratios, plasma proteins and glucose were measured through 11 days of age.

Broilers from large vs small eggs were 10% heavier and had lower mortality at 49 days of age. Chicks that were held for extended time in the hatcher had lower body weights throughout the growing period. Held chicks had 1.6% (Exp 1) and 2.1% (Exp 2) lighter body weights at 49 days of age than removed chicks. No effect on body weight was observed for egg specific gravity.

Relative bursa and spleen weights were lower in held chicks through 14 days of age. Total plasma protein (TPP) and glucose levels were higher in the held chicks at 1, but lower at 3 days of age. Heterophil/lymphocyte ratios were higher in held females at 3 and 5 days and males at 3 days of age. Females had higher TPP levels through 5 days and hematocrits through 11 days of age.