Resumo
Photo-incubation can influence the fear and stress responses of poultry. However, it is unclear how photostimulation initiated at different phases of development influences the welfare status of slow-growing broiler birds. 500 Sasso eggs were assigned to 4 treatments; some were incubated in the dark throughout incubation (TA), while TB, TC and TD were photo-stimulated (12L:12D) from days 1, 7, and 14 of incubation, respectively, until hatch using a 6,500k LED at 788 clux intensity. Birds were raised in 5 replicates per treatment with 16 birds per replicate using a 6,500k LED (at 28 clux) and a photoperiod of 16L:8D. Fear (emergence, tonic immobility, isolation and inversion tests) and stress response (physical asymmetry) of 10 birds per treatment were examined. At the end of the three-week brooding, all parameters measured were not significantly influenced (P > 0.05) by the onset of photo-incubation. At slaughter age (12 weeks), physical asymmetry was significantly higher (P < 0.05) in TA compared to the other treatments. The frequency of isolation vocalisation was significantly lower (P < 0.05) in TB compared to TA, and latency to rightness during tonic immobility was significantly higher (P < 0.05) in TA compared to the other treatments. Latency to emerge was significantly longer (P < 0.05) in TA compared to TC and TD. The frequency of wing flaps during inversion was significantly higher (P < 0.05) in TA and TD. Conclusively, photo-incubating eggs reduce stress and fear, and initiating photo-incubation during the first phase of incubation is more beneficial.