External and Internal Quality and Chemical Composition of Hen Eggs as Related to Hen Age and Selection for Production Traits

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Abstract
The composition of eggs and total production were examined from 26 wk until 61 wk in the 4th generation for 2 lines of hens selected for egg number and egg weight, respectively, and the corresponding control line. In the egg weight line, significant changes were found in the weights of the egg, albumen, yolk and shell and in concentration of solid in yolk. These traits increased by 12, 13, 11, 8 and 1 percentage units, respectively. In the same line the concentration of phospholipid in yolk and protein in solids of albumen significantly decreased by 3 and 1 percentage units, respectively. In the line selected for higher egg number, the shell weight, the concentration of protein and cholesterol in yolk, and the concentration of solid and protein in albumen were significantly lower than in the control line. A significant increase in percent protein in yolk with increasing age was found in all 3 lines; concentration of solid in yolk was increased with increasing hen age, but only significantly for the control line and the egg weight line. The total lipid concentration, concentration of cholesterol in yolk and concentration of protein and solid in albumen decrease significantly with increasing hen age. Selection for egg number decreased the total amount of solids in the albumen and increased the total amount of solids in the yolk. The daily excretion of cholesterol per hen was almost the same in the examined lines. The total production of cholesterol per hen from the age 1st egg laid until 42 wk, was 26.45, 27.85 and 24.64 g for the egg weight line, egg number line and control line, respectively. The repeatability coefficients for traits such as concentration of cholesterol, total lipid and phospholipid were very low. Small differences between repeatability coefficients were evident between the 3 lines. The most divergent coefficient was that the concentration of cholesterol in the egg weight line, for which the value was calculated to be 0.19. Phenotypic correlations between different production traits and/or chemical components are shown.

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