Table 4.

Effects of dietary leucine levels on the villus height, crypt depth and V:C ratio of broilers' duodenum at different days.

Item	Group
	1.37TM	1.77TM	2.17TM	2.57TM
Villus height, μm
d 7	623.99 ± 23.68	619.57 ± 12.03	614.15 ± 24.43	611.69 ± 12.73
d 14	892.32 ± 37.59b	853.38 ± 54.93ab	868.09 ± 27.40ab	807.85 ± 50.52a
d 21	901.24 ± 70.54	884.90 ± 50.95	907.51 ± 24.77	874.19 ± 40.84
Crypt depth, μm
d 7	100.59 ± 7.40	102.89 ± 9.28	99.76 ± 5.98	96.67 ± 8.90
d 14	158.87 ± 8.68b	127.36 ± 5.74a	128.40 ± 7.23a	137.63 ± 13.44a
d 21	164.13 ± 7.55bc	151.12 ± 11.39ab	138.50 ± 11.97a	176.42 ± 9.90c
V:C
d 7	6.22 ± 0.32	6.06 ± 0.47	6.17 ± 0.40	6.37 ± 0.50
d 14	5.62 ± 0.23a	6.70 ± 0.17b	6.78 ± 0.31b	5.90 ± 0.49a
d 21	5.49 ± 0.30ab	5.87 ± 0.34b	6.61 ± 0.75c	4.96 ± 0.11a

1.37TM = 1.37% leucine in the nutrient composition, etc; V:C = the ratio of villus height to crypt depth.

^a,b,c Within a row, means with different superscripts differ significantly (P < 0.05).