Effect of group size on performance and egg quality of laying hens during 20 to 36 weeks of age

The aim of this study was to improve knowledge on the effect of group size on productive performance and egg quality of hens raised in furnished cages equally designed. A total of 520, 15-week-old Lohmann Brown laying hens were divided into 2 groups to have a similar initial body weight (average 1392 +/- 16.3 g). The cages of S25 group (240 L x 78 W x 50 H cm, 749 cm(2)/hen) hosted a total of 200 hens, while those of S40 group (462 L x 65 W x 50 H, 751 cm(2)/hen) included 320 birds. Experimental data were recorded after an adaptation period of 5 weeks (20 to 36 weeks of age). Hens were submitted to 15 h of light/d. The average temperature inside the building was 24.6 +/- 2.5 degrees C over the entire experimental period with higher values at 24, 26, 28 and 30 weeks of age. The relative humidity recorded inside the building was 55% at week 20 and 60% all through the experimental period. Hens raised from S40 group had lower percentage of egg production (84.91 vs 88.90%, P<0.01) and higher feed conversion ratio (2.70 vs 2.25, P<0.0001) than S25 group. The percentage of eggs laid out of the nest was higher in S25 than S40 group (0.26 vs 0.19%, P<0.01). As expected, the week of age affected almost all the parameters (feed intake, body weight, laying percentage, egg weight, yolk, shell and albumen indexes, shell thickness, Haugh unit). However, the effect of group size was particularly evident during the hot period.