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By Naheeda Portocarero, UK
While we know that light intensity has an impact on behaviour and physiology, there is debate surrounding the optimum level that should be used. A comparison of different light intensities; 1, 10, 20 and 40 lux carried out at the University of Saskatchewan showed that birds exposed to 1 lux rested more and showed reduced foraging, preening, dust-bathing, stretching and wing-flapping behaviours in comparison to birds exposed to brighter light intensities.
These birds also had bigger and heavier eyes. While there was no effect of light intensity on skeletal health, deep ulcerative footpad lesions decreased linearly as light intensity was increased. And although diurnal rhythms of serum melatonin were unaffected, these results suggest that very low light intensities can compromise the welfare of birds.
Intensity influences behaviour
In practise, however, long periods of dim lighting are commonly used, despite a growing awareness that moderate-length photoperiods with brighter light intensities could benefit the welfare of the birds. Work at the University of California looked at the effects of long and moderate photoperiods at dim and bright light intensities on behaviour and health of broilers. The long photoperiod consisted of 20 hours light and 4 hours dark, while the moderate photoperiod was made up of 16 hours light and 8 hours dark. The dim photoperiods consisted of 1 lux during the day and 0.5 lux during the night whereas the bright photoperiod was 200 lux in the day and 0.5 lux at night.
There were no differences in feed conversion ratio, but the birds subjected to dim lighting were around 70g heavier than those in bright light. The birds in bright light were more active and fed more during the day but less active and fed less at night than those reared with dim light. Birds on low light intensity had larger and heavier eyes than those receiving bright light. These results suggest that light intensity, rather than photoperiod, has more influence on broiler behaviour and eye health and that very low intensity appears to dampen behavioural rhythms.
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