5Tauson R.. Health and production in improved cage design [J] . PouhSci, 1998, (77): 1820 -1827.
6Fleming R. H. , Whitehead C. C. , Alvey D. , et al. Bone structure and breaking strength in laying hens housed in different husbandry systems [J] . Br Pouh Sci, 1994, (35) : 651 - 662.
7Tauson R. , Abrahamsson P.. Foot and skeletal disorders in laying hens. Effects of perch design, hybrid, housing system and slocking density [ J]. Acta Agric Scand Section A Anita Sci, 1994, (44) : 110 -119.
8Webster A. B.. Welfare implications of avian osteoporosis [J]. Pouh Sci, 2004, 83(2) : 184- 192.
9Appleby M. C. , Hughes B. O.. Welfare of laying hens in cages and alternative systems: Environmental, physical and behavioural aspects [ J ]. World' s Poult Sci J, 1991, (47) : 109 - 128.
