Hybrids Generated by Crossing Elite Laying Chickens Exhibited Heterosis for Clutch and Egg Quality Traits

ABSTRACT Crossbreeding advantage in hybrids compared to their parents, termed heterosis, has been exhaustively exploited in chicken breeding over the last century. Reports for crossbreeding of elite laying chickens covering rearing and laying period remain infrequent. In this study, resource populations of Rhode Island Red (RIR) and White Leghorn (WL) pure-bred chickens were reciprocally crossed to generate four distinct groups that were evaluated for pre-laying growth, egg production, and egg quality. Birds monitored for pre-laying growth consists of 105 (RIR), 131 (WL), 207 (RIR × WL) and 229 (WL × RIR), and 30 pullets from each group were evaluated. Egg laying records were collected from 102, 89, 147, and 191 hens in the four populations, respectively. In addition, expression of five candidate genes for egg production in the ovarian follicles was measured by RT-qPCR. Results showed that BW of hatched chicks in the WL line was higher than the other populations. However, the two crossbreds grew faster than WL purebred throughout the pre-laying period. Low to medium heterosis was observed for BW and body length before the onset of lay. WL and the hybrids commenced laying earlier than RIR pullets, and egg production traits were favorable in the crossbreds compared to purebreds. Heterosis for egg number and clutch size was moderate in WL×RIR but low in RIR × WL hens. Expression of anti-mullerian hormone gene was high in WL and RIR×WL hybrids, suggesting WL parent-specific enhancing dominant expression. Shell weight was higher in the crossbreds than purebreds at 52 wk of age but RIR hens laid eggs with higher shell ratio than the other populations (P