Many aspects of broiler health improve with decreasing day length, i.e. longer periods of dark, according to a paper published in Poultry Science in January 2013.

Karen Schwean-Lardner of the University of Saskatchewan in Canada and co-authors there and at Aviagen in the US studied the effects of day length, sex and genotype (Ross × Ross 308 and 708) on mortality causes, bird mobility, footpad health and ocular size, in four trials within the experiment.

Four graded day lengths were chosen to allow the study of relationship between day length and health parameters, including (hours of light:hours of dark) 14L:10D, 17L:7D, 20L:4D and 23L:1D. The primary statistical tools used to assess the day length relationships were regression analysis (Proc Reg and RSReg of SAS).

Data were also analysed as a 4 (lighting programme) × 2 (sex) × 2 (genotype) factorial arrangement.

Total mortality, as well as mortality due to metabolic and skeletal disease, decreased linearly with increasing inclusion of darkness in the periods 7 to 32 days, 7 to 38 days and 7 to 48 days.

Infectious disorders were quadratically related to day length in the period 7 to 48 days only, with birds under 20L having the highest level.

Day length was linearly or quadratically related to average gait score in a positive fashion, and the incidence of birds falling in painful gait score categories increased linearly with increasing day length.

Average footpad lesion scores increased with increasing day length (28 and 35 days).

The 23L photoperiod resulted in heavier eye weights than other lighting programmes.

Males had a higher mortality and morbidity rate and a higher average gait score than females. Average footpad score was lower for males than females (at 28 and 35 days).

Overall mortality was higher for 308 than 708 broilers; hence, levels of specific mortality causes were higher. Average gait scores were lower for 308 than 708 birds in two of the three time periods measured and footpad lesions were higher.

Reference

Schwean-Lardner K., B.I. Fancher, S. Gomis, A. Van Kessel, S. Dalal and H.L. Classen. 2013. Effect of day length on cause of mortality, leg health, and ocular health in broilers. Poult. Sci. 92(1):1-11. doi: 10.3382/ps.2011-01967

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