Table 6.

Effects of different dietary CP levels on the serum biochemical indices of laying ducks at the end of the trial (61 wk).

Variables	CP level (%)1					SEM	P-values
	17.5	16.5	15.5	14.5	13.5		ANOVA	Linear	Quadratic
TP (g/L)	53.4	55.0	55.9	59.5	57.8	0.94	0.286	0.044	0.120
ALB (g/L)	16.8	17.3	17.4	19.3	19.3	0.38	0.090	0.007	0.028
UA (μmol/L)	259	268	246	249	279	5.60	0.329	0.614	0.329
CRE (μmol/L)	39.1a,b	37.9a,b,c	40.0a	34.5c	34.9b,c	0.60	0.002	0.003	0.008
AST (U/L)	25.0	29.2	35.6	34.1	33.8	1.35	0.068	0.016	0.015
ALT (U/L)	29.5b	35.9a	34.2a,b	35.5a,b	36.5a	0.78	0.020	0.011	0.017
TB (μmol/L)	5.22	5.77	4.85	7.04	5.35	0.314	0.214	0.500	0.702
GLU (mmol/L)	10.0	9.99	10.2	10.3	9.90	0.140	0.943	0.988	0.856
TG (mmol/L)	5.91b	7.28b	6.72b	9.77a	7.50b	0.312	<0.001	0.008	0.009
TC (mmol/L)	2.59b	3.36a,b	3.16a,b	3.54a	2.83a,b	0.111	0.029	0.406	0.019
Ca (mmol/mL)	7.62	7.83	7.69	7.78	7.61	0.152	0.990	0.943	0.922
P (mmol/mL)	2.33	2.42	2.24	2.68	3.07	0.107	0.086	0.019	0.022

^a-cMeans within a row with differing superscripts differ significantly (P < 0.05). Abbreviations: ALB, albumin; ALT, alanine aminotransferase; AST, aspartate aminotransferase; Ca, calcium; CRE, creatinine; GLU, glucose; P, phosphorus; TB, total bilirubin; TC, total cholesterol; TG, triglycerides; TP, total protein; UA, uric acid.

¹Mean of 6 replicates (2 ducks per replicate) per treatment.