Effect of Tier Level on the Performance and Egg Quality Traits of Laying Hens in Different Seasons

The aim of the present study was to determine the influence of tier level on the performance and egg quality traits of laying hens in different seasons. A total of 288 Lohmann hens were used and placed into 3-tier cage (T=top, M=middle, B=bottom). The measurements obtained herein for 12 months showed that the air quality and temperature changed depending on the season. Sure enough, as the outdoor temperature of poultry houses lowered in the winter season, the indoor temperature of poultry houses decreased. The lower values of CO2, NH3 and H2S of poultry houses in the summer increased in winter season, and also the relative humidity increased. While the egg production of hens caged at the T tiers was higher (P 0.05) in the winter and autumn seasons, this parameter was high (P 0.01) for hens housed at the T and M tiers in spring season. But, the hens at the T and M tiers consumed more feed (P 0.01) in the spring. Considering the tier levels, there was no difference in the feed conversion ratio during all the seasons. While the eggs of hens reared at the T and M were lighter in winter, but the eggs of hens at the T tier in spring, summer and autumn became lightened. In the assessments of the inner and outer quality of egg, the shape index and Haugh unit did not differ among the cage tiers during all the seasons. The eggshell of hens raised at the B tiers was thicker in summer. On the other hand, the stiffness of eggshell in the spring at the T tiers was higher. In conclusion, although the laying hens caged at the T tiers in winter, spring and autumn seasons had higher egg production than that of hens kept at the L tiers, the feed conversion ratio (FCR) being the most critical criteria of the performance traits, was not affected by tier levels.