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Abstract
Eggs from three commercial and two experimental strains of laying hens were sampled four times during 420 days of laying period when the hens were 25, 42, 58 and 78 weeks of age. Each strain was given one of 5 isocaloric (11.3 MJ ME/kg) diets with crude protein (CP) levels of 12.4, 13.7, 15.0, 16.3 and 17.6% and corresponding lysine contents of 0.46, 0.56,0.66,0.77 and 0.87%. The diet with 0.66% lysine was supplemented with 0.1% lysine HCl, and compared with the unsupplemented 0.66 and 0.77% lysine diets only when fed to the commercial strains. The effects of age, strain and diet were investigated on; shell quality as measured by shell weight (SW), thickness (ST), weight/unit of surface area and deformation (DFM) and interior quality as measured by albumen height (AH), Haugh units (HU), yolk colour (YC) and incidence of blood and meat spots (BMS). Chemical composition was analysed as protein, lipids and solids in yolk, albumen and total egg liquid (TEL). Features causing down-grading of the eggs were registered at the farm as shell-less (SL), damaged and visibly cracked (DVC), and double-yolked (DY) eggs. Cracks detected upon candling (CUC), undersize (<50 g) and dirty eggs were registered at the local packing station. Age and strain of bird significantly influenced all traits studied except the frequency of SL eggs, yolk protein and lipids concentration, which were not affected by strain. Dietary CP level highly significantly influenced the following traits; egg weight, AH, HU and YC values, SW, percent shell of total egg weight, incidence of DY eggs, protein concentration in TEL, yolk and albumen, and concentration of solids in the albumen. The only consistent differences between the commercial and experimental strains were in AH, HU, proportion of yolk and, consequently, the concentration of TEL lipids and solids. However, no strain by dietary CP level interactions were found for most traits studied.
