Can Eggshell Quality be Determined by Shell Color?

Problem

* Is there a relationship between eggshell color and eggshell quality?
* Is computer-based image analysis technology a reliable indicator of shell color?

Introduction

Throughout the world, preference for a shell color in table eggs has differed and is based mainly on the visual appeal of the egg. For example, in North America the preference is for white-shelled eggs while in Asia the preference is for brown-shelled eggs. Shell color has very little to do with the nutritional value of a table egg. But is there a possible relationship between eggshell quality and shell color?

Previous studies have shown that there is a correlation between shell color and shell quality in eggs of a single strain. The overall finding was that darker brown eggs had a higher shell quality than lighter brown eggs. Shell quality was determined by specific gravity, egg weight loss (due to storage) and shell strength. While an association was found, it was too small to conclude that shell color was a more reliable measure of shell strength than specific gravity. Also, the measurement of shell color used in these past studies was subjective and may have been biased.

Approach

To determine if a relationship exists between eggshell color and eggshell quality, four different strains of broiler breeders were used. Each strain was subjected to three different feeding programs. The four strains of broiler breeders used in this study were the Cobb 500, Shaver Starbro, Hubbard Hi-Y and Avian 24K. To maintain anonymity, these strains were randomly and irrespectively assigned a code of either W, X, Y, or Z. These birds were part of a larger study (by Dr. Frank Robinson) testing the effects of different feed treatments on four strains of broiler breeders. The three feeding programs were ad libitum (AL), fast feed (FF) and slow feed (SF).

At 50 weeks of age, eggs were collected and weighed over a one-week period. The eggs were weighed and their specific gravity was determined. Shell color was determined using image analysis software, Northern Exposure (Empix Imaging Inc.). An egg was placed in a small (2.5 cm) aluminum cylinder with its large end up. A video camera placed directly above the egg records a picture of the egg and projects this image onto a computer monitor. The image was saved in black and white and stored for future measurements. The computer recorded a total of 818 images. Shell color was assessed as an average gray value on a scale of 0 to 255; with 0 being black and 255 being white. Average gray value was referred to as shell color units (scu) for the purposes of this study (Figure 1). After the images were taken, each egg was opened, the yolk and albumen were emptied and the shell was rinsed under warm water and placed in egg flats to dry so that they can be weighed.

Specific gravity was not influenced by feed treatment. This was unexpected, as the AL fed birds laid the largest eggs of the three groups (Figure 2), we assumed that they would have a lower specific gravity. The AL fed birds also produced the lightest eggshell color than either the FF or SF groups (Figure 3). There were strain differences in shell color with strain W producing the darkest colored eggshells and strain X producing the lightest. However, differences in shell color across strains or feeding programs could not be consistently correlated to any specific shell quality parameter (i.e. specific gravity, shell weight or egg weight loss).

Image analysis was an effective tool for measuring shell color in broiler breeder eggs. Strain appeared to have a great influence on shell color but it was not the only factor involved. There are several experiments that are being proposed to further study the effects of shell color on shell quality.

By Nancy Joseph (Source: Poultry Research Centre News - Vol. 7 No. 2)
Published on the Government of Alberta Agriculture and Rural Development website