International Journal of Poultry Science 9 (2): 139-147, 2010 ISSN 1682-8356 © Asian Network for Scientific Information, 2010 Corresponding Author: G.N. Rayan, Department of Poultry Production, Faculty of Agriculture, Ain Shams University, Cairo, Egypt 139 Impact of Layer Breeder Flock Age and Strain on Mechanical and Ultrastructural Properties of Eggshell in Chicken G.N. Rayan, A. Galal, M.M. Fathi and A.H. El-Attar Department of Poultry Production, Faculty of Agriculture, Ain Shams University, Cairo, Egypt Abstract: This investigation was carried out to study mechanical eggshell traits (weight, specific gravity, eggshell thickness and eggshell breaking strength) and ultrastructural properties from layer breeder hens at different ages (25, 47 and 61 weeks). The present results showed that the brown eggshell had significantly higher specific gravity, shell thickness and breaking strength compared to white eggshell. Concerning breeder flock age, it could be noticed that the age of hen significantly affected mechanical eggshell traits, where specific gravity, shell thickness and breaking strength decreased significantly as the breeder age was advance. With respect to eggshell ultrastructural properties, the brown eggshell had significantly higher effective thickness (palisade %) compared to white ones. Opposite trend was observed for relative cap thickness. With regard to layer breeder flock age effect, the results indicated that the effective thickness (palisade %) was significantly decreased as the layer breeder flock age increased. Conversely, the relative cap thickness was increased with age increased. With respect to confluence trait, the present results observed that both brown and white eggs owned shells with similar values of confluence. Significant difference observed between strains regarding fusion (early or late) trait. Type B's, type A's and alignment traits in eggshell produced from older breeders was significantly higher that of younger breeders. Key words: Eggshell traits, breeder hen age, older hens INTRODUCTION The breeding programme for laying traits paid a considerable interest to the shell quality. Economic losses associated with the incidence of eggshell defects are important when evaluating the profitability of a layer operation (Bell, 1998; Flock, 1995; Seeland et al., 1995). Low egg quality almost leads to a 5-8% loss in production (Krshavarz, 1994). The frequency of defective eggs may increase from 7-11% during the laying, collecting and packing stages of egg production. Thus shell quality is one of the major problems of egg production. Maintaining quality eggshells throughout the production cycle is desirable. Avian eggshell contains organic (3.5%) and inorganic (95%, almost calcium carbonate) fractions; it weighs about 5 g and contains 2.2 g calcium, which represents about 38% of its weight (Nys et al., 1999). Many factors have been found to affect eggshell quality, such as disease, nutritional status of the flock, heat stress and age (Roberts, 2004). A decrease in eggshell quality of older hens has been reported by Elaroussi et al. (1994). Egg production rate decreases and egg weight increases as age advances, also egg composition change and shell thickness decrease with production level and age of layer (Summers and Leeson, 1983; Seeland et al., 1995; Machal and Simeonovova, 2002). The decline in eggshell quality as the hens’ age may in part be attributed to reduced intestinal calcium uptake as well as to increased egg size (Al-Batshan et al., 1994). The increase in shell weight as hens’ age was not sufficient to compensate for the increment of egg weight, so that the ratio of shell weight to egg weight decreased (Roberts and Blaney, 2000). Ultrastructural studies have demonstrated that the eggshell is comprised of there morphologically distinct calcified layers (Solomon, 1991; Dennis et al., 1996; Fraser et al., 1999). Bain (1991) suggested that the organization of the palisade columns is a major determinant of shell stiffness and therefore of shell strength. Shell strength is directly related to shell thickness (Khatkar et al., 1997) and the palisade layer comprises approximately two-thirds of the eggshell (Parsons, 1982). Therefore, it is likely that alterations in the thickness of the palisade layer, independent of structural reorganization of the palisade columns, could affect shell strength. Recent Transmission Electron Microscopy (TEM) studies (Dennis et al., 1996; Fraser et al., 1999) have revealed columnar calcite crystals in a vertically aligned matrix associated with the vertical crystal layer. Therefore, the objectives of this research were to investigate the effects of breeder hen age and strain on mechanical and ultrastructural of eggshell in laying hen breeder hens under prevailing Egyptian conditions.