Egg Shell Strength

Abstract

Three experiments are reported which were designed to measure the relationship that exists between the specific gravity of an egg and deformation of its shell under load and also to determine the extent to which these two egg characteristics are related to shell breakage in the field. A very close relationship was shown to exist between egg specific gravity and egg shell deformation. In experiments 1 and 2, measurements of specific gravity and shell deformation were performed upon samples of eggs produced by groups of birds housed in wire‐floored pens and by individual birds kept in battery cages and were found, with one exception, to be significantly related to the incidence of cracking under these field conditions. The one non‐significant correlation was that between egg shell deformation and percentage cracks among eggs from the various pens of birds. However, too much emphasis should not be placed on this latter result because the incidence of floor‐laying in the different pens was not uniform and this increased chance variation in the occurrence of cracking. In experiment 3 specific gravities and shell deformations were determined on 3000 sound eggs before they were subjected to treatments that simulated the hazards encountered during (a) laying in battery cages, (b) transport in the conventional travelling boxes. Both measurements were found to forecast fairly accurately the probability of a particular egg becoming cracked or remaining sound during the treatments. The results confirm that egg specific gravity, as measured by the hydrometer method, is a reliable assessment of shell strength and suggest that the measurement of shell deformation is of comparable reliability. Other factors of practical significance that would influence the choice between the two assessments are discussed.