Body weight trajectories on behavioural and physiological indicators of broiler breeder females.

The objective of this study was to evaluate effects of relaxed feed restriction, achieved by modifying growth trajectories, on feeding behaviour and welfare indicators of broiler breeder females. Two simultaneous experiments (Exp 1 and Exp 2) used a precision feeding system and target body weight (BW) trajectories derived from a 3-phase Gompertz model fitted to the Ross 308 recommended target. Exp 1 used a 6 × 2 factorial design, with six continuous coefficients for age at maximum pubertal growth: I2 = 15, 17, 19, 21 (Ross 308 standard), 22, and 23 wk; and two discrete early growth shift treatments (EG). In EG0, prepubertal (g1 = 1.77 kg) and pubertal (g2 = 1.98 kg) gains followed the Ross 308 standard target. In EG20, 20% of g2 was shifted to g1. Exp 2 used a 6 × 2 factorial design with six continuous EG shifts: -10, 0 (Ross 308 standard), 10, 20, 30, and 40% of g2 shifted to g1; and two pubertal growth rates: standard b2, or 50% faster (b2 150%). Average daily station visits, meals, meal size, and successful visits were summarized for rearing (3 to 22 wk) and laying (23 to 60 wk). Heterophil-to-lymphocyte ratio (H/L) was measured in five birds per treatment at 16, 20, 22, 24, 26, 28, 30, and 32 wk, and plasma corticosterone (CORT) at 16, 20, 24, and 28 wk. During rearing, feed-seeking behaviour, measured as station and successful visits, decreased as BW targets increased in both experiments. In Exp 1, H/L decreased by 0.05 for each week I2 was advanced, and CORT at 16 wk decreased by 149.6 pg/mL per week of advancement. In Experiment 2, H/L decreased by 0.007 per percentage-point increase in EG, and CORT from 16 to 28 wk decreased by 9.70 pg/mL per percentage-point increase. Relaxed feed restriction during rearing therefore reduced feed-seeking behaviour and improved physiological stress indicators.