Effects of modifying layer cages with solid sides on stress physiology, plumage, pecking and bone strength of hens

This experiment evaluated the welfare of layer hens housed in cages modified with solid sides. Welfare was assessed on the basis of physiological measures of stress [corticosterone concentrations 'at rest' and in response to adrenocorticotrophic hormone (ACTH) and heterophil: lymphocyte ratios)] and immunological responsiveness, feather condition and cover, bone strength, claw length and between-bird pecking behaviour. Factors examined were cage modification (solid sides v. open sides i.e. standard cages), tier (upper v. lower), birds (1 or 2 birds/cage) and age (commencing at 35 v. 60 weeks of age). The cages provided a floor area of 1504 cm(2). Floor pens (2.5 by 2.5 m) with 10 birds/pen served as an external control treatment. Solid sides in cages reduced the level of stress, compared with both standard cages and floor pens, based on lower corticosterone concentrations (2.2 v. 3.4 and 4.4 nmol/L, respectively) and lower heterophil: lymphocyte ratios (1.36 v. 1.66 and 1.66, respectively) (P<0.05). The ACTH response data reflected a lower level of stress in the solid side compared with the pen treatment (P<0.05). Feather condition and cover were improved by the presence of solid sides compared with standard cages (P<0.05), were similar to the floor pen treatment and were probably a consequence of reduced pecking behaviour both within (65%) and between cages (86%) (P<0.05). Solid sides had no effects on immunological responsiveness, claw length or bone strength. The experiment showed that solid sides can have a positive effect on welfare by reducing the level of stress, decreasing between-bird pecking and improving feather condition and cover. However, another study showed mortalities increased in cages with solid sides during hot weather.