Variation in Egg Yolk Colour in Different Systems of Rearing Laying Hens

Abstract

A total of 72 laying hens (ISA BROWN hybrid combination) were divided into two groups. Thirty-six layers in the first group were reared on litter while the second group of layers was reared using the cage rearing system. Samples of eggs were collected from both groups for a period of seven months. Yolk colour was determined using a portable spectrophotometer using a newly developed method, which complied with the CIELAB system. Yolk colour indicator L* decreased for the rearing system on litter, i.e. egg yolk colour became darker in the course of the whole experiment (α = 0.05). Indicator a* showed a distinct increase in the case of the rearing system on litter, with the differences being significant (α = 0.05) over the last three months of the experiment. Differences for the whole experiment were highly conclusive (α = 0.01), as seen from the increasing red colour intensity. Similarly, indicator b* also increased, i.e. egg yolk was of more distinct yellow colour. In the case of the cage-rearing system, egg yolk colour indicators correlated well with egg weight indicators, as compared to the rearing system on litter. The rearing system on litter resulted in significantly increased intensity of orange colour compared to the cage rearing system.