The Influence of an Increasing Photoperiod, a Modified Natural Daylength and Feed Restriction during the Rearing Period on the Performance of Five S.C.W.L. Genotypes

Abstract

Three tests involving approximately 7,000 S.C.W.L. birds were used to study three light treatment effects as follows: (1) a photoperiod that was gradually increased during the rearing period; (2) a modified natural photoperiod for Northern Hemisphere spring-hatched birds with the photoperiod decreased during the latter part of the rearing period; and (3) a constant 14-hour photoperiod from hatching to the end of the laying test. Restricting feed during the rearing period was also compared with full-feeding. Five commercial egg production genotypes were used in each of these experiments.Increasing the photoperiod during the rearing period was detrimental to general performance and reduced returns over costs when compared with a constant 14-hour daylength.The comparison between a 14-hour constant daylength and a modified simulated natural daylength which included a declining photoperiod during part of the rearing period, was not conclusive, although the latter treatment appeared to be somewhat superior to the constant 14-hour daylength.Although the birds on feed restriction returned more income over feed costs compared with full-fed birds, the difference was not significant and the effect was not considered important enough under conditions of this experiment to offset the extra cost of imposing feed restriction, however, in an environment in which the photoperiod cannot be controlled, feed restriction may be used to offset disadvantages associated with an adverse daylength.Evidence is presented which indicates that genotype × photoperiod interactions may be important.It is concluded that in windowless houses, photoperiodism can be used effectively to achieve optimum performance among S.C.W.L. egg production genotypes without the necessity of using a rearing period feed restriction program.