Comparison of physical quality and composition of eggs from historic strains of single comb White Leghorn chickens.

The effect of long-term genetic selection on physical quality and composition of eggs was determined by analyzing eggs acquired from Agriculture Canada: Ottawa Control Strain 5 (CS5) from a 1950 base population, 7 (CS7) from a 1958 population and 10 (CS10) from a 1972 population. Eggs from the H&N "Nick Chick" current commercial strain (CCS) were also included. Eggs were collected monthly over a 62-wk laying period and analyzed for egg, albumen, shell and yolk weight; albumen protein, solids and pH; percentage yolk solids and fat; Haugh units; and specific gravity. Significant (P < 0.05) differences found between strains included a progressive increase in weight of eggs from the CS5 to CCS. Although the eggs increased in size, no significant differences were found between strains for specific gravity or percentage shell weight. Yolk weights of eggs from the strains examined did not differ. However, the percentage of yolk found in current strain eggs was significantly lower (P < 0.05), with a subsequent higher percentage albumen due to the increase in egg size of the CCS. Haugh units were significantly higher in the CS10 and CCS strains than in the other strains. No significant differences between strains were seen in albumen protein, solids, pH, or yolk solids. Mean percentage yolk fat assay values for eggs from the CS5, CS7, CS10, and CCS strains were 33.08, 32.68, 32.84, and 32.40, respectively. Percentage yolk fat values obtained from CCS were significantly lower (P < 0.05) than those obtained from the other strains. The results from this study indicate that genetic selection has produced larger eggs containing a lower percentage of yolk while overall egg quality has been maintained or improved.