This study was conducted to investigate the effects of cage stocking density on egg yield, some egg quality traits and plumage condition in laying hens. Eighteen weeks-old 264 ISA-Brown pullets were divided into four cage density groups. The densities were 2 000, 1 000, 667 and 500 cm<sup>2</sup> per hen (by allocating 1, 2, 3 and 4 hens per cage; floor area 40 × 50 cm) with 48, 30, 24 and 21 replicate cages, totally 123 three-tier battery cages. During the experimental period from 18 to 53 weeks of age, all birds were provided illumination for 16 hours a day. The hens were fed a diet containing 11.7 MJ ME/kg and 180 g CP during the period of 18 to 40 weeks of age and 11.3 MJ ME/kg and 170 g CP during the period of 41 to 54 weeks of age. Feed and water were available for <I>ad libitum</I>. Egg yield, mortality, live weights at 50% egg production age and at the end of experiment, pecking related mortalities, some egg quality traits and plumage condition were recorded weekly. Hen-housed egg production, egg mass, viability, and live weights were significantly decreased by higher densities. Most of the egg quality traits were not affected by cage densities. Pecking related mortalities increased in cage densities of 667 cm<sup>2</sup> and 500 cm<sup>2</sup> per hen compared to the other densities (<I>P</I> < 0.05) while plumage scores were higher in all body parts of hens kept in cages of 2 000 cm<sup>2</sup> and 1 000 cm<sup>2</sup> densities compared to the higher densities. The results showed that brown laying hens should be kept in cages having 1 000–2 000 cm<sup>2</sup> densities in order to improve their welfare and performance.
A COMPARISON OF THE PERFORMANCE AND SOME PHYSIOLOGICAL STRESS OF LAYING HENS KEPT IN BATTERY CAGES AND ON FLOOR PENS SYSTEM
