| China is the largest pig-raising country in the world.The main feed materials of pig breeding are corn and soybean meal,however,a large number of corn and soybean meal are dependent on imports in China.It has become a research hotspot to search for fiber-rich feedstuff to replace corn and soybean meal to reduce feeding cost.Dietary fiber(DF)is very important to maintain the intestinal barrier function and microbiota stability of pigs,and can enhance the resistance of non-ruminants to intestinal infections caused by pathogenic bacteria.Therefore,it is of great significance to find fiber feedstuffs which can reduce the feed cost and maintain the intestinal health and microbial community stability of pigs.Wheat bran is a by-product of flour milling,which is often used as the fiber component of pig diet to reduce feed cost.Defatted rice bran(DFRB)is a rich and underutilized agricultural by-product in rice refining process,which is rich in energy and DF.DFRB has prebiotic effect,and it can increase the proliferation of beneficial bacteria and reduce potential pathogenic bacteria to improve the intestinal barrier function.In this experiment,wheat bran was used as the feed fiber source to replace basal diets.Erhualian pig,Large White pig with the same body weight as Erhualian pig and Large White pig with the same physiological stage as Erhualian pig were fed with four different wheat bran level diets.The purpose was to evaluate the different response of gut physical barrier and microbiota to different fiber levels between Chinese local pigs and imported lean meat pig breeds.Then DFRB was used as fiber source to replace corn to feed Suhuai pig.Further study on the response of intestinal physical barrier function and microflora structure to fiber feed of the lean meat breed Suhuai pig was carried out to provide theoretical reference for reducing the cost of breeding and strengthening intestinal health of pigs.1.Responses of intestinal physical barriers and microbiota to different fiber levels in Erhualian pig and Large White pigTwenty-four Erhualian barrows(Er-HL,approximately 40 kg),24 Large White barrows(S-LW,the same body weight as the Erhualian pig,approximately 40 kg),and 24 Large White barrows(L-LW,the same physiological stage as the Erhualian pig,approximately 65 kg)were selected and randomly divided into 4 treatment groups including control diet group,7%,14%and 21%wheat bran replaced basal diet group with 6 replicates in each group.Pigs were fed by the Osborne Testing Stations System(OTSS).OTSS can accurately record daily intake and body weight for each pig.Therefore,each pig was considered as a replicate.After the 28-d trial,blood samples were collected for the measurements of endotoxin,diamine oxidase(DAO),and Dlactate.The middle sections of the cecum and colon were collected for histological analysis.Mucosal scrapings from the jejunum and colon were prepared for measuring 16S rRNA gene copies of microbiota and the mRNA expression levels of Caspase 3,Bax and Bcl-2L1.The results showed that pig breeds had a significant effect on large intestinal morphology,intestinal permeability,and intestinal bacteria.For Er-HL,compared with the control group,7%wheat bran significantly increased D-lactate concentration(P<0.05),but the muscle thickness was increased in the cecum.14%wheat bran significantly up-regulated Bcl-2L1 mRNA expression and decreased the 16S rRNA gene copies of Escherichia coli(E.coli)in the colon.For S-LW,compared with the control group,7%wheat bran reduced intestinal wall thickness in the cecum and crypt depth in the colon(P<0.05),decreased the 16S rRNA gene copies of E.coli in the jejunum and Lactobacillus in the colon(P<0.05)and down-regulated Bcl-2L1 mRNA expression(P<0.05).14%wheat bran increased serum endotoxin concentration of SLW(P<0.05).For L-LW,compared with the control group,7%wheat bran decreased the 16S rRNA gene copies of Lactobacillus in the jejunum and E.coli in the colon,increased the 16S rRNA gene copies of total bacteria jejunum in the colon(P<0.05)and down-regulated Bcl-2L1 mRNA expression(P<0.05).2.Response of intestinal physical barrier to dietary fiber levels in Suhuai pigA total of 35 healthy Suhuai barrows(62.9±0.8 kg)were randomly divided into 5 dietary treatments including basal diet and 4 experimental diets in which corn was replaced by 7,14,21 and 28%DFRB,respectively.After a 28-d trial,blood samples were collected for further analyses of endotoxin,DAO,and D-lactate.All pigs were slaughtered and the middle section of the cecum and colon were collected for intestinal histology analysis.Mucosal scrapings from the jejunum,ileum,and colon were collected to measure the mRNA levels of Caspase 3,Bax and Bcl-2L1.The results showed that serum endotoxins and diamine oxidase(DAO)concentration were both increased with the increasing levels of DFRB(linear,P<0.05).However,compared with control group,serum endotoxins concentration and DAO activity were not significantly affected in pigs fed with 7%DFRB in the diet.There was a quadratic response in serum D-lactate concentration to the increased DFRB(quadratic,P<0.05).In the cecum,the thickness of intestinal wall and muscle thickness significantly increased with the increasing levels of DFRB in the diets(linear,P<0.05).3.Response of intestinal microbiota to dietary fiber levels in Suhuai pigAfter a 28-d trial,mucosal scrapings from the jejunum,cecum and colon were prepared for measuring the 16S rRNA gene copies of microbiota.The bacterial 16S rRNA gene sequencing was conducted for jejunal mucosa.The results showed:(1)There was no linear and quadratic response in microbial diversity index of jejunal mucosa(Sobs,Shannon,Simpson,Ace and Chao index)to the increasing levels of DFRB in the diets.However,compared with control group,the abundance indexes(Ace,Ace,and Chao)of 7%DFRB group were significantly lower(P<0.05).The principal coordinate analysis(PCoA)showed that the samples of 7%DFRB group and the control group were separated(P<0.05);(2)A total of 1653 OTU were obtained in jejunal mucosa samples,and 261 common OTU were obtained in the control group,7%,14%,21%and 28%DFRB groups.The number of unique OTU in the control group,7%,14%,21%and 28%DFRB groups were 89,102,151,147 and 151,respectively;(3)Twenty differential genus were found through Kruskal-Wallis rank sum test.Compared with the control group,the relative abundance of Escherichia-Shigella,a conditional pathogen,was significantly reduced in 7%DFRB group,and the genus Pseudomonas,Brochothrix and Sphingomonas related to fiber degradation were significantly increased;(4)In the jejunum,there was a quadratic response in 16S rRNA gene copies of E.coli and Bifidobacterium to the increased DFRB(quadratic,P<0.05).According to 16S rRNA gene copies of E.coli and Bifidobacterium,the most suitable level of rice bran replacing maize was 7.50%and 8.92%respectively.Considering that E.coli has the greatest impact on growth performance,the optimum level of DFRB to replace maize was 7.50%.In summary,there were differences in large intestinal morphology,intestinal permeability,and intestinal bacteria between Erhualian pig and Large White pig.For Er-HL,7%wheat bran significantly increased D-lactate concentration,but muscle thickness was increased in the cecum.14%wheat bran significantly up-regulated Bcl2L1 mRNA expression and decreased the 16S rRNA gene copies of E.coli in the colon to protect the microbial barrier function.7%wheat bran down-regulated Bcl-2L1 mRNA expression,decreased the 16S rRNA gene copies of Lactobacillus and E.coli of S-LW and L-LW.For Suhuai pig,7%DFRB had no adverse effect on intestinal permeability,reduced the relative abundance of Escherichia-Shigella,a conditional pathogen,increased the genus Pseudomonas,Brochothrix and Sphingomonas which was related to fiber degradation,and had a beneficial effect on Escherichia coli and Bifidobacterium.Considering that E.coli has the greatest impact on growth performance,the optimum level of DFRB to replace maize was 7.50%in Suhuai pig. |
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