Analysis of Factors Affecting Year-Round Performance of Single Comb White Leghorn Laying Hens Reared Under an Open-Sided Housing System

Abstract

Based upon a field survey, an analysis was made to clarify factors affecting year-round performance of laying hens reared within an open-sided housing system. Data were collected from flocks located in Kumagaya city (36° N, Japan), where they were subjected to periodic seasonal changes in photoperiod and ambient temperature specific to that area. Monthly performance of Single Comb White Leghorn laying hens at 5 to 16 mo of age was recorded and analyzed in terms of month of hatch, ambient temperature, and age. Changes in egg production and daily egg mass coincided with those in natural daylength. Egg weight was significantly lower in June-hatched layers; egg mass was highest in May and lowest in December hatches. Feed, CP, and ME intakes showed opposite periodic changes to that of ambient temperature with various delay times: ME intake showed no delay, whereas feed and CP intakes had 18 and 29-day delays, respectively. By comparing the performances of April to June and September to November-hatched hens, it was found that natural photoperiod appeared to be more important than ambient temperature in egg production, and that the effect of natural photoperiod became small and insignificant as the bird aged. The effect of temperature on egg production rate was found to be dependent on age of laying hens, i.e., it was more evident in old birds, especially when birds were exposed to a cold climate. Apparent age-dependent changes in the periodic element of egg production rate as related to calendar month were also shown.