Strain Differences in Egg Shell Mottling, Internal Quality, Shell Thickness, Specific Gravity, and the Interrelationships Between These Factors

The genetic basis of egg quality

“…These are discussed by Baker and Curtiss (1958) who also present their own, supporting, findings. Phenotypically there was a highly significant correlation between shell thickness and specific gravity.…”

“…A third type of texture ("glassy") has been identified, but there does not seem to be much information available about its genetic basis (Almquist and Burmester, 1934)-" Mottling " is caused by the distribution of water in the shell (Hoist, Almquist and Lorenz, 1932) and appears as translucent spots. This trait appears to be inherited as Baker and Curtiss (1958) found significant differences between the strains they studied.…”

Calcium Homeostasis in Pullets of Two Lines Selected for Differences in Eggshell Strength

“…Strain differences in eggshell strength have been demonstrated by several workers (Strain and Johnson, 1957;Baker and Curtiss, 1958;Petersen et al, I960;Washburn, 1974, 1977;Hamilton and Sibbald, 1977). Significant variation between individual hens within strains (Jenkins and Tyler,I960) permits selection for improvement in traits associated with shell quality (Johnson and Merritt, 1955;Hyre, I960;Jaffe, 1966;Gowe, 1969a, 1969b).…”

Influence of Inheritance and Age of Hen upon Initial Egg Quality

“…Some hens produce "glassy" shells that are practically nonporous (Almquist and Burmester, 1934). Other shell characteristics that have been studied involve mottling (Baker and Curtiss, 1958), for which high repeatability estimates within strains and differences between strains indicate a heritable characteristic, and smoothness of shell (Berg et al, 1949), which can be improved by a program of line selection while an oppositely selected line becomes progressively rougher. Much as a nonporous egg might be desired from a market quality standpoint, breeders are not going to try to produce them!…”

“…Studies based on these various methods of measurement have given strong evidence for inherited differences between breeds (Van Wagenen et al, 1937;King and Hall, 1955); between strains, lines and families within breeds (Farnsworth and Nordskog, 1955;Baker and Curtiss, 1958;Lorenz et al, 1934;Knox and Godfrey, 1940); and in response to selection for either good or poor albumen quality (Van Wagenen and Hall, 1936;Lorenz and Taylor, 1940;Berry, 1950). The physical state of the albumen has been measured in a number of ways: by the percentage of firm or thick white, by the height of albumen, by an albumen index, by an index of height of albumen to egg size expressed in Haugh units, and by scoring using the Van Wagenen-Wilgus chart.…”