Table 4.

Effects of dietary zinc (Zn) supplementation on the egg quality of duck breeders in the laying period (21 to 40 wk).

		Zn supplemental levels (mg/kg) 1							P-value
Variables	Time	0	10	20	40	80	160	SEM	ANOVA	Linear	Quadratic
Eggshell thickness (mm)	5 wk	0.385	0.397	0.408	0.401	0.402	0.403	0.0016	<0.001	0.064	0.018
	10 wk	0.397	0.399	0.408	0.409	0.411	0.407	0.0019	0.166	0.137	0.037
	15 wk	0.387	0.399	0.406	0.402	0.402	0.401	0.0016	0.004	0.191	0.049
	20 wk	0.384	0.393	0.394	0.392	0.396	0.395	0.0014	0.095	0.084	0.074
	Mean	0.388	0.397	0.404	0.401	0.403	0.402	0.0010	<0.001	0.011	<0.001
Eggshell breaking strength (N)	5 wk	45.3	48.7	48.8	47.0	44.6	48.9	0.55	0.057	0.617	0.332
	10 wk	43.8	42.8	44.2	43.4	41.7	41.8	0.40	0.353	0.063	0.163
	15 wk	43.1	43.6	42.3	43.4	41.6	42.8	0.36	0.612	0.514	0.492
	20 wk	37.9	42.0	38.7	38.6	39.7	38.1	0.42	0.047	0.354	0.568
	Mean	42.5	44.3	43.5	43.1	41.9	42.9	0.27	0.169	0.318	0.367
Eggshell ratio (%)	5 wk	10.0	10.2	10.5	10.1	10.3	10.2	0.055	0.250	0.674	0.755
	10 wk	9.66	9.47	9.74	9.92	10.0	9.63	0.061	0.102	0.650	0.028
	15 wk	9.58	9.78	9.71	9.46	9.42	9.59	0.055	0.411	0.438	0.271
	20 wk	9.11	9.54	9.31	9.32	9.41	9.32	0.057	0.417	0.793	0.693
	Mean	9.59	9.76	9.81	9.70	9.78	9.70	0.035	0.556	0.871	0.526
Albumen height (mm)	5 wk	6.92	6.59	6.47	6.33	6.61	6.84	0.086	0.361	0.559	0.217
	10 wk	6.27	6.20	6.27	6.33	6.19	6.51	0.088	0.928	0.374	0.594
	15 wk	6.37	6.54	6.56	6.49	6.15	6.62	0.088	0.700	0.824	0.553
	20 wk	6.21	5.79	6.01	6.11	6.05	5.98	0.086	0.839	0.895	0.980
	Mean	6.44	6.28	6.33	6.32	6.25	6.49	0.043	0.595	0.432	0.222
Yolk color	5 wk	4.83	5.00	4.78	4.94	4.78	5.17	0.061	0.419	0.169	0.209
	10 wk	4.83	5.17	5.33	5.33	5.33	5.50	0.092	0.414	0.095	0.175
	15 wk	4.40	4.46	4.38	4.50	4.19	4.38	0.055	0.718	0.533	0.629
	20 wk	4.47	4.30	4.18	4.53	4.42	4.53	0.052	0.297	0.222	0.478
	Mean	4.63	4.73	4.67	4.83	4.68	4.89	0.037	0.271	0.066	0.182
Haugh unit	5 wk	83.0	80.5	79.9	78.5	80.6	79.9	0.70	0.596	0.529	0.538
	10 wk	76.6	76.3	76.8	77.3	75.8	76.5	0.64	0.993	0.860	0.975
	15 wk	77.2	77.9	79.8	78.7	77.0	79.2	0.53	0.623	0.645	0.849
	20 wk	76.9	73.9	75.9	75.9	74.8	74.9	0.58	0.769	0.589	0.834
	Mean	78.5	77.2	78.1	77.6	77.1	77.6	0.305	0.791	0.612	0.599

¹Mean of 6 replicates (5 eggs per replicate) per treatment.