LAUSR

ABSTRACT 1. This study investigated the impact of photoperiod on the productivity and welfare of broilers reared without antibiotics (RWA). 2. A total of 8,064 mixed sex Ross 308 broilers were allocated to two trials. Lighting treatments were 14L:10D, 17L:7D, 20L:4D or 23L:1D. 3. Significance defined when P ≤ 0.05 and trends noted when P ≤ 0.10. Highest body weights and feed consumption were found in the 4D treatment. Longer dark periods resulted in improved feed conversion. Uniformity was improved with 1D. 4. Heterophil/lymphocyte ratios were highest in birds reared on 1D. Longer photoperiods negatively impacted gait and footpad scores. Birds spent more time performing feeding behaviours under longer photoperiods. Birds reared under 1 and 10D spent more time standing while those under 4 and 7D spent more time preening. Birds raised on 4D spent more time environmental pecking, while object pecking occurred more under 10D. Condemnations were lowest in birds reared under 7D. 5. In conclusion, rearing RWA broilers on longer photoperiods negatively impacted welfare, as indicated by poorer mobility, higher stress, more severe footpad lesions, and altered behaviour.