Relationships Between Laboratory Measures of Egg Shell Strength and Breakage of Eggs Collected at a Commercial Grading Station

Abstract

During eight visits to a commercial grading station, random samples were taken of 60 intact and 30 cracked eggs from each of 35 shipments of eggs. The samples of eggs were taken to the laboratory where egg and shell quality measurements were obtained. Details concerning each shipment, such as age(s) and strain(s) of the flock(s), were provided by the manager of the grading station.Egg breakage (damaged shells but intact membranes) reported by the grading station was 3.1% for the 760,000 eggs in the shipments with a range of 1.3 to 6.3% for the 35 shipments. The distributions of egg size in the samples and the shipments were similar, indicating that the sampling procedure worked satisfactorily. Of the measures that could be obtained from damaged eggs (egg weight, shell weight, percent shell, specific gravity, and shell weight per unit area), all but egg weight showed highly significant (P<.01) differences between intact and cracked eggs. However, the ranges of values of the two types of eggs overlapped extensively. Correlation coefficients between egg breakage in the shipments and the means of the egg and shell quality measurements of the intact eggs were highest (.591) with egg weight; the coefficients with percent shell, specific gravity, deformation, and quasi-static compression fracture strength were –.416, –.437, .309, and –.391, respectively. The magnitude of the coefficients increased somewhat when calculations were restricted to data from shipments of eggs from flocks of a single age. Except for deformation, the partial correlation coefficients, adjusted for age, were much smaller than those ignoring age. The results of this study suggest that laboratory measures of shell quality made on samples of eggs are inadequate as predictors of shell breakage of the sampled populations during commercial processing.