Genetic Parameters of Egg Shell Quality Traits and Percentage of Eggs Remaining Intact Between Oviposition and Grading ,

Abstract

This study was performed to estimate heritabilities and genetic as well as phenotypic correlations of the egg shell quality traits specific gravity (SG), nondestructive deformation (DFM), compression fracture strength (CFS), shell weight (SW), percentage shell (% shell), and shell weight per unit surface area (SW/SA) and percentage of eggs remaining intact (% intact) from oviposition to placement in fiber trays after grading. In the first year of the 2-yr study, eggs were obtained from about 1,000 F1 hens from each of two crosses of selected Single Comb White Leghorn strains (01 × 03 and 02 × 04) when they were 42 and 68 wk of age. At each age, the shell quality of eggs collected on Sunday for 3 consecutive wk was measured whereas eggs collected Monday through Thursday of each week passed through egg washing, candling, and grading equipment before being hand candled to determine % intact. Eggs from F2 daughters were measured in a similar manner the following year.Heritability estimates tended to be highest (.29 to .59) for SG, SW, % shell, and SW/SA, somewhat lower (.21 to .33) for CFS, and lowest (.10 to .26) for DFM and % intact. Absolute phenotypic correlations between egg shell quality traits and % intact ranged from .19 to .47 whereas genetic correlations ranged from .23 to 1.04. Estimated genetic correlations between % intact eggs late in the laying year and egg shell quality traits early in the laying year were .50 and .62 (SG), .47 and .59 (CFS), .45 and .49 (% shell), –.37 and –.46 (DFM), .42 and .43 (SW/SA), and .23 and .30 (SW). Taking into consideration heritability, genetic correlation, and ease of measurement, the best shell quality trait for use in selection programs for improving % intact is SG.