Table 5.

Effects of different dietary CP levels on the serum hormones 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
Estradiol (ng/L)	54.5	48.6	50.5	47.9	41.6	1.84	0.272	0.039	0.116
Follicle-stimulating hormone (IU/L)	1.52	1.58	1.50	1.59	1.35	0.039	0.299	0.205	0.192
Luteinizing hormone (U/L)	3.63a	2.76a,b	2.69a,b	2.46a,b	1.92b	0.160	0.008	<0.001	0.002
Prolactin (mIU/L)	158a	119b	103b	91.1b	95.2b	5.20	<0.001	<0.001	<0.001
Progesterone (ng/mL)	17.1a	15.6a,b	12.3b	13.9a,b	11.2b	0.61	0.005	0.001	0.003

^a,bMeans within a row with differing superscripts differ significantly (P < 0.05).

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