The albumen, yolk, and shell percentages were
calculated using the individual weight of each egg
and the weight of its components. The shell weight
was measured after drying at 50°C for 2 h. The shell
strength (g/cm2
) was measured using a destructive
method that was performed with a QC-SPA apparatus
(TSS, York, UK). The shell thickness (mm)
at the equatorial plane was evaluated using a QCT
micrometer (TSS) after removing the inner and
outer egg shell membranes. The egg shell index
was calculated after Ahmed et al. 2005:
SI = (SW/S) × 100; S = 4.68 × EW2/3
where:
SI = egg shell index (g/100 cm2
)
SW = shell weight (g)
S = shell surface (cm2
)
EW = egg weight (g)
The albumen height and Haugh units (Haugh
1937) were evaluated using a QCH device (TSS).
The yolk height (mm) was measured using a digital
micrometer head (Mitutoyo, Kawasaki, Japan). The
formula for the albumen index (AI; %) calculation
is as follows:
AI = {albumen height/[(long diameter of albumen +
+ short diameter of albumen)/2]} × 100
The yolk index (YI; %) was calculated using the
formula:
YI = (yolk height/yolk diameter) × 100
The yolk to albumen ratio (YAR; %) was calculated
as:
YAR = (yolk weight/albumen weight) × 100
Eggs for the measurement of microbial egg shell
contamination were collected at 7 h every four
weeks, nine times per experiment (from July to
March), four eggs from each treatment; 36 eggs
per treatment (9 × 4) and 144 eggs per experiment
(9 × 4 × 4) in total. Eggs were randomly collected