Effect of lighting stress on fluctuating asymmetry, heterophil-to-lymphocyte ratio, and tonic immobility duration in eleven breeds of chickens.

The purpose of the present study was to analyze the effect of a lighting stress on the fluctuating asymmetry (FA), the heterophil-to-lymphocyte ratio, and the tonic immobility duration of chickens. The experiment (440 birds) measured the FA of several traits (outer, middle, inner, and hind toe lengths and leg, wing, second primary feather, and spur lengths), the heterophil-to-lymphocyte ratio, and the tonic immobility duration in 36-wk-old hens and cocks of 8 Spanish breeds of chickens (Black-Barred Andaluza, Black-Red Andaluza, Black Castellana, Buff Prat, Red-Barred Vasca, Red Villafranquina, Birchen Leonesa, and Blue Leonesa), a synthetic breed (Quail Castellana), a White Leghorn population, and the e(y) tester line, which had been housed in continuous light (24L:0D) or in a light-dark regimen (14L:10D) for 16 wk. There was a significant difference between lighting treatments in both females and males on the combined FA of the 4 toes (P < 0.01) and the combined FA of toe, leg, wing, feather, and spur (in males) lengths (P < 0.05), the FA of birds housed under continuous light being greater than that of control birds. There was a significant difference (P < 0.001) for the heterophil-to-lymphocyte ratio and the tonic immobility duration between lighting treatments, the ratio being higher and the duration being longer in the group of birds housed under continuous light. Thus, birds exposed to continuous light were more stressed and fearful than control hens. Results were consistent across the breeds and indicate that a continuous light regimen seriously negatively affects the welfare of birds.