The aim of this study was to investigate the effect of group size and stocking density on the welfare and performance of hens housed in furnished cage systems during summer. A total of 924 Hy-Line Brown hens were assigned to three housing systems: a standard battery cage system (control, 4 hens per cage and 398 cm 2 per hen), two furnished systems (including perches and nest); one with a small (SFC, 21 hens per cage; 586 cm 2 per hen) and one with a large group size (LFC, 48 hens per cage; 543 cm 2 per hen). The results showed that hens housed in SFC and LFC had a higher feed intake and a poorer feed efficiency compared to control hens. Laying rate and egg weight were not significantly affected by housing systems. Hens housed in LFC and SFC systems showed less sitting and more walking behaviours than control hens. SFC hens showed more nesting and less perching behaviours than LFC hens. Hens kept in SFC systems showed fewer signs of heat stress during summer, with less panting activity than LFC or control hens, and a relatively lower rectal temperature than controls. The rectal temperature of LFC hens did not differ from the SFC hens and controls. Blood concentrations of luteinising hormone, follicle-stimulating hormone and oestradiol were not significantly influenced. In conclusion, group size and stocking density in furnished cages have an effect on behaviour and performance of hens. The furnished cage systems with small group sizes were favourable for hen welfare without markedly affecting performance. Group size should be considered in the development of furnished cage systems.

This article is available online at http://www.jlr.org secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus stimulates the release of the pituitary gonadotropins, luteinizing hormone (LH), and folliclestimulating hormone (FSH), which in turn activate gonadal development and release of sex steroids, including estradiol (E2) and testosterone. Stress is a common problem disrupting breeding in either wild birds or domestic chickens ( 1 ). Glucocorticoids (GC), as the fi nal effectors of the hypothalamic-pituitary-adrenal axis, participate in the control of whole body homeostasis and the arousal of stress responses. GCs transmit information about environmental conditions to the HPG axis, which ultimately infl uences the timing of breeding.Female kittiwakes with low baseline LH levels and elevated levels of baseline corticosterone (CORT), the main form of GCs in avians, were more likely to skip breeding ( 2 ). An experimental reduction of CORT release during the prelaying period was associated with an advancement of egg laying in female kittiwakes ( 3 ). In domestic chickens, an acute infusion of CORT resulted in a pause in laying and a severely reduced ovarian weight ( 4 ). Chronic and repeated exposure to CORT during the rearing phrase suppressed reproductive performance, resulting in a delay of fi rst egg laid and a reduction of egg production ( 5 ).In avians, the development of ovarian follicles is accompanied by the deposition of a large amount of yolk. During a laying cycle, follicular development is matched with a supply of yolk precursors. Triacylglycerols (TG), the main