Responses to abrupt changes in feeding and illumination in laying hens

This study aimed to investigate the responses to abrupt changes in feeding and illumination during the egg-laying period. Six hens were housed individually in cages under constant environmental conditions, with a photoperiod of 15 h (0400-1900) and ad libitum access to food for 10 days. Then the same hens were subjected to a feed withdrawal trial (between 1200 and 0830), followed by a 5-h reduction in the photoperiod (0400-1400). The heart rate (HR), body temperature (BT), and locomotor activity (LA) of the laying hens were measured continuously using radiotelemetry, with simultaneous recording of the time of oviposition. Behavioral responses to sudden changes in the management program during the pre- and post-laying periods were also recorded. Hens with restricted access to food had significantly lower HR, BT, and LA during the pre- and post-laying periods than hens given unrestricted access to food. In the pre-laying period the behavioral activity counts for cage pecking and preening were significantly higher, and feeding and drinking counts were significantly lower in the hens with restricted access to food than in the hens given unrestricted access to food. During the post-laying period the behavioral activity count in preening was significantly higher in the hens with restricted food access than in those given unrestricted access to food. Experimental hens subjected to a reduced photoperiod had significantly higher HR and BT during the pre-laying period than those under the normal light regime. During the pre- and post-laying periods hens subjected to light reduction had significantly lower LA than the hens subjected to the normal light regime. In the pre-laying period the behavioral activity count for circling was significantly lower and the preening count was significantly higher in the hens subjected to light reduction than in the hens subjected to the normal light regime. The post-laying period occurred during the light period and thus the behavioral activities were similar in the hens subjected to light reduction and those under the normal light regime. Mean onset of egg laying in all groups exposed to food withdrawal or darkness was delayed by 34 min in the food reduction trial and by 11 min in the light reduction trial, as compared to the hens during the control period. These results suggest that changes in the management program might lead to stress and impair the welfare of hens.