Effects of different housing systems on visceral organs, serum biochemical proportions, immune performance and egg quality of laying hens

The experiment was conducted to investigate the effects of different housing systems on visceral organs, egg quality, serum biochemical proportions and immune performance of laying hens. A total of 180 25-week-old Hy-Line laying hens were randomly divided into 2 groups (free-range treatment and cage-reared treatment) with 6 replicates per group and 15 hens per replicate. At 42 d of the experiment, four hens per replicate of each group were selected randomly to collect blood samples from wing for physicochemical analysis of serum biochemical parameters, and slaughtered to analyse growth of organs and immune parameters. At the same time, six eggs per replicate of each experimental group were collected randomly to measure egg quality. Body weight of free-range treatment was significantly lower than that of cage-reared treatment (P<0.05). In contrast, the proportions of proventriculus, gizzard, liver, spleen, duodenum, jejunum, ileum, cecum, and rectum of free-range treatment were significantly higher than those of cage-reared treatment (P<0.05). The albumen height and eggshell thickness of eggs from free-range treatment were significantly higher than those of eggs from cage-reared treatment (P<0.05). The concentration of triglycerides was significantly lower in free-range treatment than in cage-reared treatment (P<0.05). The two raising systems had no effect on serum concentration of IL-2 (P>0.05), but mRNA level of IL-2 gene expression in spleen of free-range treatment was significantly higher than that of cage-reared treatment (P<0.05). The results indicate that the free-range raising system could improve visceral organ, egg quality, and immune performance in laying hens.