. 2021 Oct 29;101(2):101573. doi: 10.1016/j.psj.2021.101573

Table 2.

Mechanical properties and chemical composition of eggshells in young (36 wk of age) and aged (70 wk of age) ducks.

Variables¹	Young duck	Aged duck	P-value
Mechanical properties
Egg weight (g)	66.6 ± 0.79^b	71.5 ± 2.0^a	<0.001
Shell weight (g)	6.11 ± 0.125	6.26 ± 0.217	0.125
Shell proportion (%)	9.19 ± 0.152^a	8.75 ± 0.205^b	<0.001
Breaking strength (N)	40.1 ± 1.98^a	37.3 ± 1.41^b	0.006
Shell thickness (without membrane, mm)	0.354 ± 0.012^a	0.322 ± 0.007^b	<0.001
Membrane thickness (mm)	0.105 ± 0.003^a	0.049 ± 0.003^b	<0.001
Fracture toughness (N/mm^3/2)	512 ± 34.0^a	460 ± 20.9^b	0.003
Chemical composition
Matrix proteins (mg/g)	9.94 ± 2.14^a	3.85 ± 1.01^b	<0.001
Calcium (%)	37.2 ± 0.62^a	36.2 ± 0.24^b	0.004
Phosphorus (%)	0.17 ± 0.012^a	0.15 ± 0.019^b	0.047
Magnesium (%)	0.26 ± 0.009^a	0.23 ± 0.015^b	0.002
Copper (μg/g)	13.8 ± 1.32	13.1 ± 1.77	0.456
Manganese (μg/g)	0.72 ± 0.08	0.65 ± 0.05	0.088
Zinc (μg/g)	1.69 ± 0.418	1.45 ± 0.416	0.340

^a-b

Values within a row with no common superscripts differ significantly (P < 0.05)

Mean of 6 replicates (10 eggs per replicate) per treatment.