Body weight optimization of broiler breeder hens. 2. Reproductive performance

The objective of this study was to evaluate the effect of shifted gain from the pubertal to prepubertal phase (early growth; EG) and timing of maximum pubertal growth (inflection point of a second growth phase; I2) on BW, feed efficiency, carcass composition, and reproductive performance of broiler breeder hens. Target BW trajectories were designed by changing coefficients of a 3-phase Gompertz model fit to the recommended Ross 308 BW target, [Formula: see text] . In each phase i, biologically relevant coefficients describe the amount of BW gain (g_i), the rate of growth (b_i), and the inflection point (I_i), which is the age (wk) when the growth for that phase is at its peak. The study had a 6 × 2 factorial arrangement of treatments, with six I2 levels (I from phase 2) and two EG levels. The I2 coefficients were 15, 17, 19, 21 (standard), 22, and 23. The EG treatments were: EG0, where g₁ and g₂ coefficients estimated from the standard breeder recommended BW were unchanged; and EG20, where 20% of the gain (g₂) in phase 2 (pubertal phase) was shifted to phase 1 (g₁; prepubertal phase). Two-hundred-eighty-eight Ross 308 pullets were randomly assigned to the twelve BW growth trajectories and fed using a precision feeding system from 0 to 60 wk of age. Weekly BW was analyzed using three-way ANOVA (EG, I2, and age as fixed sources of variation). Analysis of covariance was conducted on the remaining dependent variables with EG as fixed effect, I2 as a continuous fixed effect, and age as continuous effect. The observed BW followed the BW target trajectories for most of the experiment duration. Dorsal feather score decreased by 0.11/wk of earlier I2. Egg production, egg weight, and egg mass increased by 0.83%, 0.09 g, and 0.54 g/d for every week of earlier I2, respectively. Total eggs produced and estimated chick number per hen increased by 3.6 eggs and 4.4 chicks for every week of earlier I2, respectively. In conclusion, advancing BW gain around the pubertal phase of growth in modern broiler breeders increased egg and chick production.