Observations on Daily Variation in Feed Intake and Shell Strength of Eggs from White Leghorn Pullets and Force Molted Hens

Abstract

Variation in feed intake, egg and shell weight, and five estimates of shell strength were measured over 14 days in one experiment and 56 days in another. Forty-eight force molted hens were used in the first experiment, and 36 pullets and 36 force-molted hens in the second. Shell thickness (STK), specific gravity, nondestructive deformation, quasistatic compression fracture strength (CFS) and specific strength (CFS/STK) were used to measure shell strength. In both experiments, birds from two strains were used; in the second, two rooms were used with the strains and age of bird balanced across rooms.Plots of the daily means and the ranges showed systematic variation from day to day with marked changes occurring within a few days. The differences among days were significant (P<.01 in most cases) for all variables measured in both experiments, except for egg weight in Experiment 1 (P>.05). Little evidence was found of a relationship between feed intake and shell quality. There were few significant interactions (P<.05) between strain, age, or room and day. These results show that research on egg shell strength should be planned so that systematic daily variation is not confounded with treatment comparisons.