Investigation of the effect of hen's age on physical and mechanical properties of eggs

Abstract

Introduction: The egg is one of the highest quality protein sources in human diet. The eggshell is a complex structure that performs important biological functions such as protecting its internal contents and helping the chicken embryo grow. Also, during storage and incubation, it controls the exchange of water and gas through the pores and provides good resistance to mechanical
shocks and prevents microbial attack. Aging in laying hens increases the damage of the eggshell and damage to the eggshell poses serious problems for egg consumers, so maintaining the quality of the eggshell is an important principle in the laying hen industry. The aim of this study was to evaluate the effect of hen’s age on the physical and mechanical properties of eggs.
Materials & Methods: For this study, Bovans commercial laying hens were used. Relevant data were collected using 120 eggs in different weeks of production (22, 66 and 77 weeks) and analyzed in a completely randomized design with three treatments and 40 replications. Experimental treatments included three age groups: 1) 22 weeks, 2) 66 weeks and 3) 77 weeks.
Results: The results showed that the effect of hen’s age on the physical properties of eggs (length, width, shape index, geometric mean diameter, equivalent diameter, arithmetic mean diameters, sphericity, surface area, weight, volume, and density) was significant (P˂0.05), So that at 77 weeks of production of the main dimensions of the egg (length and width), geometric mean
diameter, equivalent diameter, arithmetic mean diameters, surface area, weight, and volume had the highest value (P˂0.05), also the lowest value of the index Shape, sphericity and density were observed at 77 weeks of age (P˂0.05). In addition, the mechanical properties of the eggs including rupture deformation, rupture force, rupture energy, and toughness were affected by the hen’s age
(P˂0.05) but the hen's age had no significant effect on stiffness (P˃0.05). The highest amount of rupture deformation was observed at the ages of 22 and 66 weeks (P˂0.05). With age, rupture force, rupture energy, and toughness decreased, so that the lowest values were observed at the ages of 66 and 77 weeks (P˂0.05).
Conclusion: The results of this experiment showed that the physical and mechanical properties of eggs are highly dependent on the age of the chicken at production. As the egg ages, the size of the egg increases but the shell's strength decreases, which can lead to shell damage, infiltration of contamination during storage, or incubation. Although physical properties such as weight and
geometric mean diameter reach their maximum at 77 weeks of age, the values of their mechanical properties are low, so the most suitable egg quality was at 22 weeks of age.