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. CIELAB, spectrophotometer, food colour, litter, cageQuality indicators of eggs depend not only on the nutrition of laying hens and intravital factors but also on the rearing system used.According to Wan Den Brandt et al. (2004), it is more difficult to maintain stable quality of eggs in the outdoor rearing system than in the cage rearing system. He investigated the effect of two rearing systems (outdoor vs. cages) on indicators such as egg weight, egg white, egg yolk, the content of the egg shell, the level and the pH of the white, and dry matter content of the white and the yolk. Characteristics such as egg weight, the content of the shell, the level and the pH of the white, and the levels of dry matter in the white and the yolk correlated with the age of layers and the rearing system. Yolk colour of eggs from layers reared outdoors was significantly darker.The quality of eggs from white (LSLs) and brown layers (LTs) reared in three different housing systems (cages, aviaries, and intensive outdoor rearing) were compared. LSLs gave eggs of better quality as compared to LTs. LSLs showed significantly higher levels of Haugh units (HU) (91.62), egg yolk weight, strength and density of the shell but had significantly lower values for egg yolk colour (12.9) and the occurrence of eggs with meat and blood spots was lower. The comparison of egg quality traits for the rearing systems investigated revealed that none of the systems had superior advantages over the others. The egg yolk weight was increased in the cage system. The highest colour intensity of egg yolk was found in the outdoor rearing system with LSLs and in the cage rearing system with LTs (Leyendecker et al. 2001).Quality indicators of eggs were also monitored in the ISA Brown layers in the cage rearing system,...

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