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. / Master of Science

Relationships among glucose tolerance, plasma insulin, and plasma glucagon were examined in chicks developed through selection for high (HW) and low (LW) body weight, and in F, crosses (HL) between HW males and LW females. At 21, 42, 63, and 84 days of age, chicks from each population were intubated with glucose (2 g/kg body weight) following a 24-hr fast. Blood was collected at 20-minute intervals up to 100 minutes postadministration. At all ages, the LW chicks were better able to metabolize glucose than their HW counterparts, while the HLs exhibited intermediate responses. Impaired glucose tolerance in the HWs and HLs was not associated with insulin insufficiency; the HWs and HLs, in comparison to the LWs, were hyperinsulinemic at 42 and 63 days of age and plasma insulin levels did not differ among populations at 21 or 84 days of age. Plasma glucagon responses to glucose administration were inconsistent, but plasma glucagon levels were consistently higher in the HWs and HLs than in the LWs. It was concluded that excessive fat deposition in chickens selected for rapid growth is associated with hyperinsulinemia and insulin resistance. / Master of Science