The effect of 23 h light-dark cycle on egg production and egg characteristics in the domestic fowl.

Abstract

In order to investigate the effect of 23h light-dark cycle on egg production and egg characteristics, 480 White Leghorn birds of 17 weeks of age were divided into two groups and maintained under 23 (15L:8D) and 24 (15L:9D)h light-dark cycle respectively up to 65 weeks of age. Rate of lay was 2-3% less and egg weight was 1-2g heavier under 23h light-dark cycle compared to that under 24h light-dark cycle. Yolk weight/egg weight was slightly heavier under 23h light-dark cycle than 24h light-dark cycle. Shell strength was almost the same under the both light-dark cycles. Mean oviposition interval was almost the same under the both light-dark cycles, but the variation among individuals was larger sig-nificantly under 23h light-dark cycle than 24h light-dark cycle. Genetic correlation between the trait under 23 and 24h light-dark cycle in various periods or ages was 0.3-0.5 for rate of lay, 0.5-0.8 for mean oviposition interval, 0.6-1.0 for egg weight and egg compositions, and 0.7 for shell fracture force. Genetic correlation between the trait under 23 and 24h light-dark cycle was of high magnitude in the trait with high heritability. There were three birds which laid eggs over 100% under 23h light-dark cycle on 24h basis from 181 to 300 days of age and 15% of the birds laid eggs with intervals of less than 24h under 23h light-dark cycle.It should be considered that the birds of high egg production potential could be iden-tified by using light-dark cycle less than 24h as a selection environment for laying birds.