Effect of the production system on the quality of the fresh commercial brown-shell egg

The normal behavior of birds is limited when housed in cages, as they are limited for mating, incubation and caring for their chicks; the only thing that endures as reproductive compulsion is the activity of laying eggs (Singer, 1991).
Concerns regarding the welfare of laying hens are growing due to the current reproduction system based on cages; some changes to the facilities and bird management methods, have been proposed.  Such changes have been driven by the demands of the new type of consumer who is concerned about the welfare of the production animals and the quality of the food they consume. Alternative systems have come out such as "enriched cages" that provide birds additional elements such as beds, perches and nests.   
The use of enriched cages was suggested to give birds the opportunity to express their natural behaviors, without the disadvantage of letting them free in a natural environment (Roll et al., 2007).
The objective of this work was to evaluate the effect of the laying site (nest or cage) on the internal quality of fresh commercial brown-shell eggs.

The study was carried out at the Laboratory of Animal-origin Products of the Technology Department of the School of Agrarian and Veterinarian Sciences, (FCAV) UNESP, Jaboticabal, São Paulo, Brazil.  Forty fresh brown-shell eggs from Isa Brown layer hens of around 70 weeks old were used.  The eggs came from two production systems, namely cages or bed + nest.  The eggs were evaluated based on the eggshell strength, by using a Texture Analyser TA-TX2, that measured the necessary force to break eggshells in Kgf. The parameters related to the internal quality of the egg were evaluated such as yolk color, yolk and albumin pH, yolk index (gem index, IG) and Haugh units (HU) after breaking every egg on a special table made of flat and smooth glass.  The height of the albumin and yolk was measured with a micrometer and the yolk diameter with a digital gauge.  The yolk color was obtained using a Minolta Chromer Meter CR-300, that uses system CIELAB (L*, a*, b*) and also with a DSM color fan. To obtain the Haugh Units (HU) the equation UH=100log (H+7.57-1.7W^0,37) was used, were H = height of dense albumin in millimeters and W = egg weight in grams for IG (IG = yolk height/yolk width). In order to determine the following ratios: shell:egg, yolk:egg and albumin:egg, the yolk and albumin were weighted individually with an accurate scales as well as the eggshells after washing and drying them at ambient temperature for at least 24 hours.  The eggshell thickness was evaluated on three points of the equatorial region of the egg with a Mitutoyo micrometer with a 0.01 a 10 mm scale.
The experimental design was totally random with two treatments (laying on nest or cage) and  20 replicates each one, by using the variance analysis and comparing the measurements with the Tukey test at 5% probability, with the SAS software (1999).

We can see that there was no difference (P>0.05) among eggs coming from the different laying systems regarding the yolk color.  Yolk and albumin pH was superiorly higher on the eggs coming from the nest as compared to those from the cage (Table 1).

Table 1. Values of yolk color (L*, a*, b* and DSM color fan), yolk and albumin pH of fresh commercial brown-shell eggs from nest or cage.  

Since pH is a quality parameter of commercial eggs, we can say that the results are similar to the ones found by Coutts y Wilson (2007), who state that recently-laid eggs have an albumin pH between 7.6 and 8.5, and a yolk pH close to 6.0.

Table 2. Values obtained for the percentage of yolk, albumin and shell, yolk index (IG) and Haugh units (UH) of fresh commercial brown-shell eggs from nest or cage.

We can see that even when there was no significant difference between the treatments on the IG and HU parameters, eggs from the cage had a higher amount of yolk height and width and higher albumin quality, which coincides with Alleoni and Antunes (2001), when they say that the higher the value of Haugh Units, the better the internal quality of the egg.  

Coutts and Wilson (2007) state that fresh eggs upon leaving the farm, have on average from 75 to 85 Haugh units. These values are higher than those found in our work. The results were the expected ones, since eggs were laid by old hens at the final laying phase, they have a lower internal quality than those from younger layers. 

The results of this study show that the laying equipment did not interfere with the yolk and albumin percentage, but had an effect on the eggshell percentage.  In spite of a higher eggshell:egg ratio from cage eggs, the treatments did not interfere with the eggshell thickness, according to the results shown on Table 3.

Table 3. Results of the thickness and strength of the fresh commercial brown-shell eggs from nest or cage.   

Even when there were no statistical differences (P>0.05) for eggshell thickness, the results show that eggs from the cage have a thicker shell and therefore higher strength than eggs from the nest, that have a thinner eggshell leading to a higher incidence of cracked or broken eggs.

The production system does not have a significant effect on the internal quality of the egg. Eggs laid on nests are more susceptible to breakage as the eggshell presents lower strength.   

Alleoni ACC & Antunes AJ. 2001. Unidade Haugh como medida da qualidade de ovos de galinha armazenados sob refrigeração. Scientia Agrícola 58:681-685.

Coutts JA & Wilson GC. 2007. Ovos de ótima qualidade - Uma abordagem prática. Queensland, Austrália. 65p.

Roll VFB, Briz RC, Levrino GAM, Roll AP. 2007. Uso de gaiolas enriquecidas para poedeiras comerciais. Disponível em: <http://www.aveworld.com.br/aveworld/artigos/post/uso-de-gaiolas-enriquecidas-para-poedeiras-comerciais_1360>. Acesso em: 12 fev. 2011.

SAS - Statistical Analysis Systems. 1999. User's Guide. North Caroline: SAS Institute Inc.

Singer P. 1991. Animal liberation. Rev. ed. New York: Harper Perennial - Avon Books, 320 p.