EFFECTS OF CHANGES IN PHOTOPERIOD AND FEEDING OPPORTUNITY ON THE PERFORMANCE OF 2 BREEDS OF LAYING HEN

1. ISA Brown and Shaver 288 hens, fed ad libitum, were given a 5-h inc rease or a 2, 5 or 10-h decrease in photoperiod at 215 d of age. Hens of both breeds were also maintained on constant 10, 13 or 18 h photope riods. Other groups had their photoperiod increased from 8 to 13 h, or were held on constant days but had their access to food limited to 8 h per day. 2. Both breeds on ad libitum feeding exhibited curvilinear rate of lay and egg output, and linear food intake, responses to photo period change. Shaver hens reduced their egg output and rate of lay to a greater extent than ISA Brown hens when photoperiod was decreased. 3. In both breeds the beneficial effect on egg production of the 5-h i ncrease in photoperiod was less than the adverse effect of the 5-h dec rease. 4. The influence of light change per se generally had a greater effect on performance than the influence of feeding opportunity, but significant effects of changing feeding opportunity were demonstrated. 5. The reduction in mean rate of lay and egg output following a reduc tion in photoperiod was partly caused by some birds ceasing lay, but a ll birds showed some decrease in both variates.