| The experiment was conducted to study the effects of corn particle size on the laying performance, gastrointestinal characteristic of laying hens in corn-soybean diet. A total of 774 pink-shell Lohmann commercial laying hens with 38 week-old were randomly allocated by laying rate to 1 of 3 treatments with 6 replicates of 43 laying hens each. The broilers were fed different experimental diet for 16 weeks, then one hen per replicate was chosen to determine the effect of corn particle size on the feed passage rate in hens. The corn was processed by hammer mill to 3 particle sizes in average particle diameters that included coarse (1001.70μm), medium (824.97μm), and fine (671.56μm).Feed intake (112.29,108.82,107.67g/d, P=0.001)and laying rate (94.47,92.39,90.78%, P=0.006) were increased highly significantly with the increase of corn particle size, while there was no significant difference for feed conversion ratio (P=0.528),average egg weight (P=0.799) and average body weight gain (P=0.514) among treatments. Corn particle did not affect the egg special gravity (P=0.555),eggshell pressure (P=0.702) and haugh unit (P=0.238), but the Egg yolk ratio was highly significantly dereased as corn particle size decrease (28.01,28.27, 27.68%,P=0.009). The empty relative weight of proventriculus was decreased (P=0.545) as dietary corn particle size increased. On the contrary, the increasing of corn particle size could improve the empty relative gizzard weight (13.52,12.31, 12.01g/kg BW,P=0.055) with significant heavier (P=0.024) for coarse corn than fine corn. There were no significant effects on relative empty weights of duodenum (P=0.244), jejunum (P=0.677) and ileum (P=0.754) and the entire small intestine (P=0.472).As corn particle size increased the crypt depth of duodenum (P=0.159) was decreased while the villus height (P=0.276) and villus/crypt ratio (P=0.158) of duodenum were increased. The wall thickness of duodenum (311.18,305.30, 288.86μm,P=0.078) and proventriculus (998.77,941.95,900.39μm,P=0.083)were decreased numerically as dietary corn particle size decreased. Corn particle size could reduce the ulcer score of gizzard (1.42,1.58,2.33,P=0.059), and hens fed coarse corn had significant lower ulcer score of gizzard than hens fed fine corn (P=0.027).The pH-value of contents in proventriculus (P=0.747) and gizzard (P=0.102) were decreased as the corn particle size increased. And there were effects of corn particle size on the pH-value of contents in duodenum (P<0.125), jejunum (P=0.684) and ileum (P=0.932), with the pH-value of contents in duodenum significant higher in coarse corn fed group than medium corn fed group (P=0.050).The increase of corn particle size could elevate both the activity of H+/K+-ATPase (P=0.187) and Pepsin (P=0.105) numerically,and the pepsin activity of hens fed coarse corn was significant higher than that of hens fed fine corn (P=0.050). The decreasing of dietary corn particle size depressed the lactobacillus concentration (P=0.375) and the Bacillus bifidus concentration (P=0.557) while increased the E.coli concentration (5.81,5.46, 6.60LgCFU/g,P=0.055) of cecum contents, and the fine corn group had a significant lower E.coli concentration compared with the coarse corn group (P=0.020).As corn particle size decreased, the relative recovery rate of fecal Cr2O3 at 2h (8.43,8.96, 9.81%,P=0.025),4h(19.86,23.21,25.38%,P=0.010),6h(21.55,24.63,23.98%, P=0.023) and 8h (20.98,18.12,15.51%,P=0.086) were increased, but significant decreased at 10h (10.67,8.39,8.08%,P=0.014),12h(5.13,3.58,3.34%,P=0.034) and 16h (4.16,3.10,2.78%,P=0.028), and at 24h (P=0.458) no significant difference was found among these 3 groups. Cumulative recovery rate of fecal Cr2O3 at 2h (8.43,8.96,9.81%,P=0.025),4h (28.30,32.17,35.20%,P=0.005) and 6h (49.84, 56.80,59.18%,P=0.002) were significantly increased as corn particle size decreased, while no significant difference were found at 8h (P=0.136),10h (P=0.687),12h (P=0.943),16h (P=0.699) and 24h (P=0.799). At the condition of this study, it is concluded that the increasing of dietary corn particle size could improve the productive performance,gastrointestinal health and nutrient retention in gastrointestinal tract of laying hens.
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