Abstract
Hens of four experimental strains of White Leghorns, which had been selected into low and high specific gravity (SG) groups based on SG of eggs of the first laying year, were used in the second laying year to determine the relationship between blood ionized calcium (ICa) levels and egg shell strength. Hens were bled 2.5 hr after oviposition. Blood variables measured included ICa, pH, partial pressure of carbon dioxide (pCO2) and bicarbonate (HCO3−) of whole blood, and total calcium of plasma. Measurements on the eggs collected on day of blood sampling and on the following day included SG, egg weight, nondestructive deformation (DFM), quasi-static compression fracture strength (CFS), shell weight, and thickness.There were significant differences (P<.01) among strain means for SG, egg weight, and deformation. Hens selected for high SG eggs produced eggs with greater (P<.001) shell weight and thickness SG and CFS, and lower (P<.001) DFM than did hens selected for low SG eggs. However, there were no differences (P>.05) in acid-base balance (pH, pCO2, HCO3–), blood ICa, and plasma total calcium bertween the two SG groups even when presence or absence of forming egg shell was considered. There was a very weak relationship (r = –.21 to +.18) between blood ICa or plasma total calcium and SG, DFM, CFS, or shell thickness.
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