effects of divergent selection body weight and the quail laying eggs on some physical and mechanical properties of japanese quail eggs

introduction breeding quail and quail egg industrial production because of the high nutritional value of these products has been developing these years. considering the high demand and economical production, further development in the future is predicted. in order to design and effective utilization of the equipment for transportation, separation, packaging and storage, the physical and mechanical properties of quail eggs are needed. it is of great importance to study the factors which are influencing these properties. strength of the shell is an important factor in determination of quail egg quality. quail egg shell strength depends on several variables including specific gravity, egg weight and volume, shell thickness, weight and percentage of shell, hardness, breaking force, breaking energy, egg surface, farming conditions, type and species of birds, nutrition and geometric characteristics of eggs. materials and methods in this paper, initially in three phases, at 15 weeks, 19 weeks and 23 weeks, shell strength changes and physical properties of quail eggs on 90 quails during their first period of laying eggs were studied. measured properties were included dimensions, weight, volume, specific gravity, shell thickness, weight and percentage of shell, breaking force, breaking energy, egg surface and some other properties. in the second part the effects of divergent selection for the bird’s body weight at four weeks of age on the quail eggs of fifth generation were studied. measured properties were included dimensions, weight, volume, breaking force, breaking energy and some factors for direct and indirect measurement of strength of quail eggs. for direct measurement of the strength of eggshell of quail, two methods were employed: the first method was quasi-static compression test between two parallel plates of the universal testing machine and the second method was measuring specific gravity. in the first method, eggs were compressed between two plates using universal testing machine. the compression speed was 6 cm/min and 10 cm/min. the egg sample was placed on the fixed plate and pressed with a moving plate connected to the load cell until its rupture. in the second method, quail egg volume is measured by water displacement method, as they were weighed by digital scales and specific gravity is calculated by dividing weight per volume. results and discussion in the first part of the study, through the time from beginning to end of the first period eggs (from 15 weeks to 23 weeks) breaking energy, specific gravity of quail eggs and also flexibility of eggs against external forces increased. mass, volume, large diameter, central diameter, geometric diameter mean and surface of the shell from the beginning of the period to the end of it, remained unchanged and their mean values were respectively 12.41 gr, 11.51 cm3, 33.79 mm, 26.10 mm, 28.45 mm and 2546 mm2. from 15 weeks to 23 weeks of age, shape index and sphericity decreased. mean values of shape index and sphericity were 0.769 and 84.21% respectively. in the second part of this research, quail eggs of four weeks low body weight group were smaller and lighter than quail eggs of control group, but quail eggs of four weeks high body weight group did not show significant differences with quail eggs of control group, which suggesting greater heritability of body weight in the physical properties of the eggs. strength and specific gravity parameters in the three groups did not differ significantly from each other. the results showed that quail egg shell strength after several generations of divergent selection for body weight has not been changed. conclusion flexibility and thickness of the quail egg shell increased from the beginning of the first period to the end of the laying eggs period. this makes the eggs less vulnerable and increases their strength. in the second part of the research, it could be concluded that the physical properties of quail eggs in a divergent selection for the birds' body weight in order to weight loss is more effective compared to body weight gain group.