| Based on the comparative study of pH in digestive tract, digestive enzyme activities, caecum microorganism, anatomy organizational structure of digestive organs and intestine evacuation velocity, mechanism of difference in growth and nutrient utilization efficiency between Taihang and Hy-Line layers were investigated.120 1-day-old Taihang chicken and 120 1-day-old Hy-Line layers were randomly allocated in 4 replicates, respectively, with 30 each. On day 5,9,14,21,28,35, 42,49,56,63,77and 91, apparent nutrient digestibility, pH in digestive tract, digestive enzyme activities, caecum microorganism, anatomy structure of digestive organs and intestine evacuation velocity were measured to analyze variation regularity .The results were showed as follows:(1) Taihang chicken digestibility of fat,crude protein,Ca and P decreased by 3.16 %(P>0.05),8.99 % (P<0.01) ,8.40 % (P<0.05),11.13 %(P<0.01)in 42 day old and 2.50 %(P<0.05),8.99 % (P<0.01) ,8.40 % (P<0.05),10.90 %(P<0.05) in 91 day old compared with Hy-Line respectively. But Taihang chicken digestibility of crude fiber increased by 101.95 % (P<0.01) in 42 day old and 63.11 % (P<0.01) in 91 day old.(2) Body weight at 42d, average daily gain in 0-42d of Taihang chicken were 9.79 %(P<0.01)and 8.80 %(P<0.01)lower than Hy-Line layers, respectively. Average daily feed intake was 2.19 %(P>0.05) lower than Hy-Line layers, whereas feed conversion rate was 7.28 % (P>0.05) higher than Hy-Line layers. Body weight at 91d, average daily gain and average daily feed intake in 43-91d of Taihang chicken were 17.51 %(P<0.01),11.68 %(P<0.01),20.90 %(P<0.01)lower than Hy-Line layers, respectively. Otherwise, feed conversion rate of Taihang chicken was higher than Hy-Line layers, which increased by 7.28 % (P>0.05) from 0 day to 42 day and 12.12 %(P<0.05)from 43 day to 91 day, respectively.(3) With age old, there was no significant difference in pH at digestive tract between Taihang chicken and Hy-Line layers.(4)Activities of digestive enzymes in intestinal contents increased with age and then tended to be stable in Taihang chicken and Hy-Line layer, but time to peak was different. Maximal values of duodenum amylase, lipase and trypsin for Taihang and Hy-Line layers were attained on day 35 ,35 ,42 and 35,35,42,respectively. Maximal values of jejunum amylase, lipase and trypsin were attained on day 21 ,35 ,35 for Taihang and 28,35,35 for Hy-Line layers, respectively. Maximal values of cecum cellulose were attained on day 49 for Taihang chickens and 56 for Hy-Line layers, respectively. Taihang chicken had a lower activities of amylase and lipase compared with Hy-Line layer, which decreased by 16.81 %,10.96 % at duodenum and 6.99 %,10.90 % at jejunum respectively, but a higher activities of trypsin and cellulose, which increased by 14.71 %,17.77 % at duodenum and jejunum and 15.3% at cecum respectively.(5) Taihang chicken had a lower number of Escherichia coli, but a higher number of Lactobacillus and Bifidobacterium in cecum compared with Hy-Line layers. On day 35, 42, 56 and 63, number of Escherichia coli for Taihang chicken were significantly decreased by 11.33 %,10.30 %,8.37 %,7.30 %,6.92 % compared with Hy-Line layers (P<0.05); Compared with Hy-Line layers, On day 21,28 the number of Lactobacillus in cecum of Taihang chicken were increased by 11.22% and 7.45%(P<0.05), respectively, and on 42d the number of Lactobacillus in cecum of Taihang chicken was increased by 8.66%(P<0.01). Compared with Hy-Line layers, on day 9,14,21,42 ,77 the number of Bifidobacterium for Taihang chicken were highly significantly increased by 9.53 %,9.23 %,7.86 %,7.40 %,6.34 %(P<0.01) ,respectively, and on 28,49d the indices were significantly increased by 5.76 % and 3.16 %(P<0.05).(6) Comparative study of anatomy structure of digestive organs was discussed:①The initial average weight of digestive tract of these two varieties were 3.86 g and 4.42 g, respectively, 64.55 g and 84.11g on 91d, respectively.②Intestine segments/body weight ratio tended to reached the maximum on day 9 of Taihang chickens and on day 5 of Hy-Line layers, then decreased to be stable on day 35 and 42.③Each digestive tract/total digestive tract ration of Taihang chickens from high to low were gizzard, jejunum, duodenum, ileum ,rectum, cecum, proventriculus ,crop and pancreas, otherwise Hy-Line layers were gizzard ,jejunum, duodenum, ileum, rectum, proventriculus, cecum, crop and pancreas.④Average length of total digestive tract for Taihang chicken and Hy-Line layer were 42.58 cm,55.44 cm on day 1 and 145.58 cm,163.13 cm on day 91.⑤Increased length of digestive tract was lower than increased weight of that compared with at birth.⑥There was no significant change in different intestine segments /total Intestinal ration with age.(7) The law of intestinal villi and crypt growth at different intestine segments for Taihang chicken was consistent with that of Hy-Line layers. The highest length of villi was duodenum,then jejunum, ileum and rectum.Villus height ,crypt depth and V/C at different intestine segments increased with age, among which Villus height kept increasing; crypt depth grew rapidly in the first 28 days , then became flat 35days later; V/C at duodenum and jejunum kept increasing, and V/C at ileum tended to increase in the first 14 days and 63 days later, but kept stable from 21days to 56 days. V/C at rectum tended to decrease in the first 35 days, then increased 42 days later. Villus height ,crypt depth and V/C at duodenum, jejunum, ileum and V/C at rectum of Taihang chicken were lower than that of Hy-Line layers,but villus height ,crypt depth of Taihang chicken at rectum were higher than that of Hy-Line layers.(8) Intestine evacuation velocity of Taihang chickens was more fast than that of Hy-Line layers. Intestine contents gradually decreased with fasting time and then intestine evacuation velocity showed the same variation regularity.Intestine evacuation velocity at crop, proventriculus, gizzard of Taihang chickens were more fast than that of Hy-Line layers,but intestine evacuation velocity at rectum and cecum were lower than that of Hy-Line layers.
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