Table 4.

Effects of dietary supplementation with essential oil on egg quality of laying hens¹

Items	Treatments2				SEM3	P-value
	Control	EO100	EO200	EO400		ANOVA	Linear	Quadratic
Eggshell thickness, 10−2 mm
week 4	42.31b	44.19a	44.28a	44.69a	0.23	0.002	0.002	0.001
week 8	42.86b	44.21a	44.39a	44.54a	0.18	0.001	0.002	< 0.001
week 12	42.25 b	44.00a	44.10a	44.56a	0.20	< 0.001	< 0.001	< 0.001
Eggshell strength, N
week 4	35.51	37.02	36.95	36.72	0.32	0.322	0.314	0.217
week 8	34.24	35.63	35.10	34.58	0.38	0.804	0.980	0.536
week 12	34.00	34.89	35.65	35.84	0.39	0.330	0.089	0.176
Relative eggshell weight, %
week 4	9.43	9.67	9.45	9.55	0.058	0.430	0.795	0.915
week 8	9.26	9.52	9.44	9.57	0.051	0.135	0.065	0.136
week 12	9.26	9.68	9.55	9.62	0.063	0.075	0.125	0.107
Shape index
week 4	1.35	1.34	1.35	1.35	0.0039	0.950	0.968	0.886
week 8	1.35	1.34	1.35	1,34	0.0031	0.541	0.424	0.546
week 12	1.37	1.36	1.37	1.36	0.0026	0.374	0.106	0.261
Albumen height, mm
week 4	6.10	6.32	6.44	6.37	0.11	0.744	0.440	0.533
week 8	6.46	6.87	6.84	6.74	0.081	0.275	0.400	0.185
week 12	7.07	7.30	7.31	7.27	0.080	0.716	0.504	0.532
Haugh unit
week 4	75.88	77.51	77.93	77.36	0.89	0.873	0.628	0.705
week 8	79.08	82.21	81.38	80.32	0.59	0.266	0.772	0.231
week 12	82.93	84.74	82.17	83.94	0.67	0.564	0.859	0.959
Yolk color
week 4	5.65	5.83	5.60	5.90	0.11	0.735	0.512	0.760
week 8	5.45	5.80	5.63	5.93	0.080	0.167	0.071	0.197
week 12	4.83	4.90	4.78	4.85	0.064	0.927	0.974	0.990

¹ n = 8 replicates per treatment

² Control, hens received a basal diet; EO100, EO200 and EO400, hens received a basal diet supplemented with 100, 200 or 400 mg/kg oregano essential oil, respectively

³ SEM, standard error of the mean

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