Naturally-inspired intermittent lighting schedules to improve behavioural synchronisation in layer chicks

Naturally brooded domestic chicks spend a large proportion of time resting under and gaining warmth from their mother, spending multiple short bouts in relative darkness (Shimmura et al., 2010). In contrast, during rearing, commercial chicks experience one continuous light period each day. In this situation, behaviours become unsynchronised, with the potential for active chicks to disturb and direct feather pecks towards resting conspecifics (Riber et al., 2007; Gilani et al., 2012). Intermittent lighting (IT) schedules have the potential to mimic natural brooding and synchronise chick behaviour. Previous IT studies have used sucessive alternating periods of around 40 min L:40 min D (Malleau et al., 2007), based on field observations of wild populations (Wood-Gush et al., 1978). Chicks on this simulated brooding cycle (SBC) rested more than control chicks, with no compromise in weight or feed conversion. However SBC chicks still performed some resting during the light period, suggesting that they could benefit from a shorter light period. In the current study, we used video recordings of 27 broody hens and their chicks up to two weeks of age to determine suitable mean natural brooding patterns. We then developed an IT schedule based on these natural brooding patterns.

Eighty layer chicks (Lohmann classic) were obtained at one day old and were reared in 16 groups of five chicks for 2 weeks under either continuous (“C” 14h L:10h D, n=40) or intermittent (“IT” 8 min L:8 min D for 22h with an additional 2h D from 00:00h to 02:00h, n=40) lighting schedules. Behavioural synchronisation (% of observations in which behaviour was synchronised) was assessed on days 2, 7 and 14 and weight and feed consumption were measured throughout. At the end of the two week period, welfare outcome measures were taken; these included tonic immobility, human approach and novel obejct tests, and eye temperature response to handling.

IT chicks showed significantly higher behavioural synchronisation on days 2 (p = 0.003) and 7 (p = 0.02) than C chicks, but there was no significant difference on day 14. IT chicks also showed significantly higher weight gain (days 1-14 C: 6.26g/day, IT: 7.23g/day, p = 0.001) and a lower feed conversion ratio (days 1-14 C: 6.85g/g, IT:4.70g/g, p < 0.001) than C chicks. There were no effects of lighting schedule on welfare outcome measures. Naturally-inpsired intermittent lighting schedules are a promising tool to improve behavioural synchronisation in early rearing, with no detrimental welfare effects. However, further research is needed to determine the longer-term effects of naturally-inspired intermittent lighting schedules, including those on commercial laying hen farms.