the aim of this study was to evaluate the strength of vitelline membrane and its correlation with other morphological traits and the viscosity of egg yolk of different poultry species: goose, turkey, muscovy duck, chicken, guinea fowl and Japanese quail. vitelline membrane strength (vms) was defined as work and force after the deformation of yolk at 6 mm. Bird species affected the VMS of egg yolk. the lowest strength was measured for the vitelline membrane of goose egg yolk. there were no apparent differences in the strength of vitelline membrane for ducks, guinea fowl, chickens and Japanese quail. in contrast, the vitelline membrane of turkey egg yolk appeared to be of the highest strength. Statistically significant positive correlations were observed between VMS and yolk index, while there was no correlation between the weight of the eggs and egg yolk. the work deformation of yolk was positively correlated with the viscosity of poultry egg yolk.
Key words: egg yolk, vitelline membrane strength, yolk index, viscosityA vitelline membrane is an integral part of egg yolk, separating it from egg white (albumen). By surrounding slurry yolk, it gives a spherical shape. The structure of vitelline membrane integrity is of high biological importance. It protects the inner part of yolk against pathogens and allows the proper course of embryogenesis. During the incubation embryonic cells are responsible for structural alterations in the vitelline membrane which weaken the membrane and subsequently cause it to rupture over the embryo. After 48 h of incubation, the mechanical strength of the membrane is decreased by 73%. The factors responsible for weakening of the membrane during development have not been determined. Romanoff and Romanoff (1949)