Lines were selected from the Cornell K Single Comb White Leghorn strain for two generations for high (HES) or low (LES) eggshell strength. Laying hens of both generations showed significant differences between lines in shell breaking strength. Hens of the second selected HES generation produced eggs with significantly better shell quality than did LES hens, as measured by shell breaking strength, shell thickness, or absolute or relative shell weight. However, the two lines had similar intrauterine egg residence times and times between successive ovipositions. The LES pullets showed significantly elevated ionized calcium and total calcium concentrations in blood in response to increased dietary calcium at 18 weeks of age. These results demonstrate fundamental differences in regulation of calcium homeostasis between the HES and LES lines which may relate to selected differences in their abilities to produce strong eggshells.
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Combs et al. (1979) studied this question.
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