| Post-weaning diarrhoea(PWD)is the main factor affecting the production of piglets.Protein,as an essential nutrient for the growth,can cause diarrhea through colon fermentation and allergic reaction.Colon,which is the main part of water absorption,plays a key role in the development of diarrhea.It has been confirmed that dietary protein can be fermented and produce ammonia nitrogen(AN)in colon.However,there are few reports about the mechanism and pathway of AN to colon injury.To study the effect of dietary protein level on the concentration of AN in colon,colon injury and diarrhea of weaned piglets,96 25-day-old weaned piglets were selected and randomly divided into four groups.After 7 days of adaptive feeding,the piglets were fed diets with 18%,20%,22% and 24%protein levels respectively.The diarrhea was observed and scored throughout the whole day.The pH of gastric contents,protease and chymotrypsin activity,serum urea nitrogen(BUN)and AN,serum and colonic mucosal inflammation(IL-1?,TNF-?,IL-4,IL-10)and oxidation index(SOD,MDA,iNOS,NO),serum acute phase reaction protein(CRP),serum gastrointestinal hormone substance P(SP),motilin(MTL),gastrin(GAS)and vasoactive intestinal peptide(VIP)content were measured at 6,24,48,72 and 96 h after feeding.The results show that during the whole experiment:(1)Dietary protein level had no significant effect on the performance of weaned piglets,but ADFI was the highest and F/G was the lowest in 24% protein group(P > 0.05).The diarrhea score of piglets in 24% protein group was significantly higher than that in20% group(P<0.01 or 0.05)during 24~72 h after feeding.(2)The pH of gastric contents in 18% and 24% protein groups were significantly higher than those in 20% protein groups(P<0.01 or 0.05)except for 48 h.During the whole experiment,the activities of pepsinase and chymotrypsin in 24% protein group were lower than those in 20% protein group,and there was significant difference in pepsinaseactivity at 6 and 72 h(P<0.01 or 0.05),and chymotrypsin activity at 24 h(P<0.05).Serum SP,MTL and GAS levels in 24% protein group were higher than those in 20% protein group at 24~72 h,6~72 h and 24~96 h after feeding,respectively.Serum VIP levels in48~96 h were significantly lower than those in 20% protein group(P<0.05).The results showed that 24% protein level could decrease digestive capacity of piglets by increasing stomach pH and decreasing pepsinase and chymotrypsin activity.(3)The concentration of AN in colon of piglets in 24% protein group was higher than that in 18% and 20% group except for 6 h,and significantly at 24 and 72 h(P<0.01 or0.05).The concentration of BUN in serum of piglets in 22% and 24% protein group was higher than that in 18% and 20% group during the whole experiment.The results showed that compared with 18% and 20% protein levels,22% and 24% protein levels could increase BUN and AN concentration of piglets,and decrease protein utilization rate.(4)The concentration of IL-1? in colon mucosa of piglets in 24% protein group was higher than that in 20% group(P<0.01 or 0.05)during 24~96 h after feeding,and the TNF-? in mucosa of piglets in 24% protein group was higher than that in 20% group except for 48 h.CRP in serum of piglets in 24% protein group was higher than that in 20%protein group at 24 and 48 h(P<0.01 or 0.05).Meanwhile,the serum IL-4 of 20% protein group was higher than other three groups,and the mucosal IL-4 was lower than that of22% and 24% group at 6~72 h,significantly at 48 h(P< 0.05);the mucosal IL-10 of 24%group was lower than that of 20% group at 24 and 72 h(P< 0.01 or 0.05).(5)SOD activity in serum of piglets in 24% protein group was lower than that in 20%protein group during 24~72 h,significantly at 48 and 72 h(P<0.05).SOD activity in mucosa was lower than that in 20% protein group at 6,48,72 and 96 h.The concentration of MDA and activity of iNOS in serum and mucosa of piglets in 24% protein group were higher than those in 20% group except for 48 h.NO in serum of piglets in 24% group was higher than that in 20% group(P>0.05).In the whole experiment,NO in the mucosa of piglets in 24% protein group was higher than that in 20% group,and significantly at 6,48 and 96 h(P<0.01 or 0.05).(6)The results of pathological morphology showed that the colonic mucosa of piglets in 18% protein group had exfoliation and necrosis at 72 and 96 h,and the normal structure could not be observed at 96 h.In 20% group,only part of the colonic mucosa exfoliated,mucosal epithelial cells arranged tightly,and no inflammatory cell infiltration could be seen at 48 to 96 h.In 24% protein group,the colonic mucosa was damaged seriously.Severe symptoms were mucosal exfoliation,necrosis of epithelial cells and infiltration of inflammatory cells.Normal colonic structure could not be observed at 48 h,but repaired at72 h.(7)The results of correlation analysis showed that pepsinase activity was negatively correlated with gastric pH(P<0.01),chymotrypsin activity was negatively correlated with serum BUN and AN(P<0.01),AN was positively correlated with mucosal IL-1? and mucosal IL-1? with diarrhea score(P<0.05);mucosal IL-1? was negatively correlated with mucosal IL-10.Mucosal IL-10 was negatively correlated with diarrhea score(P<0.05).AN was positively correlated with serum iNOS,as well as serum iNOS and mucosal IL-1?(P<0.05).The results showed that diets above 20% protein level could increase the content of AN in colon and aggravate diarrhea by increasing stomach pH and decreasing the activity of pepsin and chymotrypsin.This is mainly due to the increased expression of IL-1? in colonic mucosa induced by AN,the decreased expression of anti-inflammatory factor IL-10 and the increased activity of iNOS in serum.The combined effects of inflammation and oxidation lead to colonic injury and diarrhea.Therefore,in consideration of diarrhea score,controlling dietary protein level at 20% can effectively reduce the fermentation of colon protein,reduce the content of AN in colon,alleviate diarrhea and improve production performance of piglets. |
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