Day length and intensity are commonly
manipulated aspects of the light environment in commercial
broiler production. Both influence circadian
rhythms, but it is unclear if they do this independently
or synergistically. The effect of light:dark (20L:4D,
16L:8D) and intensity contrasts (1 lx:0.5 lx, 200 lx:0.5
lx) on broiler behavior and health (n = 1,004, 4 replicates/treatment)
was evaluated. Activity was measured
using passive infrared detection, and feeding activity
was measured by the amount of feed consumed/h over
one 24-h period each week. Broilers were gait scored
and weighed at 6 wk of age. Following euthanasia, eyes
were dissected from 30 birds/treatment. Behavior and
performance were analyzed using the GLM, gait score
using the Kruskal-Wallis test, and eye measures using
a MANOVA. The 200 lx birds were more active (P =
0.03) and fed more (P = 0.001) during the photophase
but were less active (P = 0.02) and fed less (P < 0.001)
during the scotophase, than the 1 lx birds. There were