Effects of shifting pullet body weight gain from pubertal to prepubertal phase on pullet development and reproductive performance of broiler breeder hens

This study evaluated the effect of early growth ( EG ) – shifts of gain from the pubertal phase ( g 2 ) to the prepubertal phase ( g 1 ) – and pubertal growth rate ( b 2 ) on development, feed efficiency, carcass composition, and reproductive performance of broiler breeder females. Two-hundred-eighty-eight Ross 308 pullets were randomly assigned to twelve BW growth trajectories and fed using a precision feeding system from 0 to 60 wk of age. A 3-phase Gompertz model fit to the recommended BW target of Ross 308 breeders was utilized, describing growth in phase 1, 2, and 3 (prepubertal, pubertal, and postpubertal, respectively). To design 12 growth trajectory treatments in a 6 × 2 factorial arrangement, six levels of the gain coefficients and two levels of the b 2 coefficient were used. The six continuous EG shifts were in 10% increments: −10%, 0% (Ross 308 standard), 10%, 20%, 30%, and 40%. For each EG treatment, the given gain (kg) as percentage of g 2 was shifted to g 1 . The 0% shift treatment used the coefficients g 1 and g 2 that described the breeder recommended target BW. The b 2 factor had two levels: Standard, where b 2 was 100% of the estimated standard pubertal growth rate from the breeder recommended pubertal phase (Standard b 2 ); and 50% faster, where b 2 was increased 50 percent (b 2 150%). Weekly BW and carcass composition were analyzed using three-way ANOVA (b 2 , EG, and age as fixed sources of variation). Analysis of covariance was conducted on the remaining dependent variables with b 2 as fixed effect, EG and age as continuous fixed effects. Bird BW followed the target BW trajectories for most of the study duration, as ADFI differed depending on the feed amount required to achieve the respective BW trajectories. Advancing EG increased breast fleshing score and pubic bone space and decreased the number of juvenile primary wing feathers during rearing (P < 0.05). Carcass fat percent increased with advanced EG after 4 wk of age, but this difference was not observed from 20 wk onward. Neither EG nor b 2 significantly affected egg production (P > 0.05). Feed per chick produced decreased with advanced EG only when b 2 was increased (b 2 150%; P < 0.05). In conclusion, early pullet growth increased mostly muscle and skeletal characteristics, whereas reproduction efficiency was increased by advanced EG only when pubertal growth rate was also increased.