| Diarrhea in weaned piglets is one of the most difficult diseases to control in pig production.It was found that adding high doses of zinc oxide(about 3000 mg/kg)to the diet can effectively reduce diarrhea in piglets.Although high-dose zinc oxide can alleviate diarrhea in piglets,long-term excessive use of zinc oxide has an adverse effect on health in piglets,and the absorption rate is low.Most of the zinc oxide is discharged with feces,causing environmental pollution.Therefore,it is inevitable to reduce the use of zinc oxide in piglet diets.Porous zinc oxide is a kind of zinc oxide produced by a new process.Due to its porosity,it has a large specific surface area and can be more fully contacted with chyme and its pathogenic bacteria.The aim of this paper is to study its effect on the performance and diarrhea of weaned piglets and to elucidate the possible mechanism of anti-diarrhea.The method of in vivo and in vitro test was adopted,this study explores(1)the differences in intestinal tissue impedance and intestinal permeability between porous zinc oxide and common zinc oxide;(2)effects of different amounts of porous zinc oxide on performance and diarrhea of weaned piglets;(3)the mechanism of porous zinc oxide relieving diarrhea in weaned pigletsThe main findings are as follows:Part 1.Physical characteristics of porous zinc oxide and its effect on epithelial permeability of pig small intestine(1)By scanning electron microscopic scanning and specific surface area measurement of porous zinc oxide,the results show that:1)the average particle size of porous zinc oxide is 70?m,which is much larger than ordinary zinc oxide 3.6?m,which is 19.4 times of ordinary zinc oxide;2)Porous zinc oxide has a microporous structure with a specific surface area of 37.57 m~2/g,which is much larger than ordinary zinc oxide of 1.91 m~2/g,which is19.7 times that of ordinary zinc oxide.(2)Determination of jejunal tissue impedance and transmittance by porous zinc oxide and common zinc oxide by Eus perfusion.Four pigs of 21-day-old,body weight 6.0-6.5 kg Duroc×Large White/Landrace weaned pigs were selected,and the middle part of the jejunum of the piglets was collected to make three samples of 0.80 cm2 area.Three zinc oxide treatment groups(0 zinc oxide)were set up.50 mg/L ordinary zinc oxide and 50 mg/L porous zinc oxide were subjected to a Uss perfusion test.The results showed that compared with the blank control group,50 mg/L porous zinc oxide and common zinc oxide could significantly increase the jejunal tissue impedance(P<0.05),and the jejunal tissue impedance caused by porous zinc oxide was higher than that of ordinary zinc oxide.At the same time,the cumulative permeability of porous zinc oxide jejunum was significantly lower than that of common zinc oxide jejunum(P<0.05).This result means that porous zinc oxide can reduce its permeability by increasing intestinal tissue impedance and is more efficient than ordinary zinc oxide.Part 2.Effects of porous zinc oxide on growth performance,diarrhea rate and blood biochemistry of weaned pigletsA total of 192 21-day-old weaned piglets(mean weight 6.32±0.24 kg)were randomly divided into 4 treatment groups,6 replicates in each group,8 piglets per replicate,positive control group(3000 mg/kg)Ordinary zinc oxide),negative control group(0 mg/kg zinc oxide),750 mg/kg porous zinc oxide group,1500 mg/kg porous zinc oxide group,respectively.The experiment last for 14 days.The results showed that compared with the negative control group,the average daily weight gain of the piglets in the other experimental groups was significantly increased(P<0.05);the diarrhea rate was significantly decreased(P<0.05);however,there was no significant difference between the other experimental groups(P>0.05).Compared with the negative control group,the other experimental groups significantly increased serum AST and ALP activity(P<0.05)and IgG levels(P<0.05);the porous zinc oxide group significantly increased the content of cecal acetic acid and propionic acid(P<0.05);compared with the positive control group,the zinc content in the porous zinc oxide groups was reduced(P<0.05),and the difference in copper and iron content was not significant(P>0.05).The results indicated that 750mg/kg and 1500mg/kg porous zinc oxide can significantly decrease the diarrhea rate,promote the growth of piglets,which achieves the same effect as 3000mg/kg ordinary zinc oxide,as well as reduce zinc emissions.Part 3.Study on the mechanism of porous zinc oxide relieving diarrhea in weaned piglets(1)The aim of this study was to investigate the effect of porous zinc oxide on intestinal barrier function,the experimental design is the same as part 2.Compared with the negative control group,the other experimental groups significantly increased villus height in the jejunum and ileum(P<0.05),significantly reduced the ratio of villus height to crypt depth in the ileum(P<0.05),and tended to decrease the ratio of villus height to crypt depth in the jejunum(P=0.0671).Compared with the positive control group,the porous zinc oxide group significantly decreased the relative mRNA expression of IL-8 in the jejunum and ileum(P<0.05),and promoted the relative mRNA expression of TGF-?(P<0.05),furthermore,the1500 mg/kg porous zinc oxide group significantly increased the relative mRNA expression of Occludin and ZO-1 in the jejunum(P<0.05).The results indicated that porous zinc oxide has a strong anti-inflammatory effect,improved intestinal tight junction,and improved intestinal morphological structure.On the one hand,it may up-regulate the relative mRNA expression of Occludin and ZO-1 in intestinal epithelial cells by inhibiting the expression of mi R-122a,thereby enhancing the tight junction of the intestinal epithelium;on the other hand,it may reduce the extravasation of water into the intestinal lumen by reducing the mRNA expression of aquaporin AQP 3 on the cell membrane.(2)The aim of this study was to investigate the effect of porous zinc oxide on intestinal microflora,the experimental design is the same as part 2.Compared with the positive control group,the porous zinc oxide group improved the Chao1,ACE,Shannon and Simpson indices;compared with the negative control group,the porous zinc oxide group can increase the metabolism of carbohydrates in the jejunum.The relative abundance of microbial flora in lipid metabolism and enzyme family metabolism;compared with ileal contents,the porous zinc oxide group significantly increased microorganisms involved in amino acid metabolism,carbohydrate metabolism,lipid metabolism and the relative abundance of microbial flora of enzyme family metabolism in the jejunal contents(P<0.05).The results suggest that porous zinc oxide can regulate the diversity of intestinal flora;the increase of abundance of microbial flora involved in amino acid,carbohydrate and lipid metabolism means that microorganisms and their metabolites may be more conducive to optimize the structure of intestinal flora.(3)The aim of this study was to investigate the effect of porous zinc oxide on intestinal health of piglets.A total of 128 piglets(average weight 6.55±0.25 kg)were weaned at21-day-old,they were randomly divided into 4 treatment groups according to body weight,8replicates in each group,4 piglets per replicate,positive control group(3000mg/kg oxidation)Zinc),negative control group(0 mg/kg zinc oxide),200 mg/kg porous zinc oxide group,500mg/kg porous zinc oxide group,respectively.The experiment last for 28 days.The results showed that compared with the negative control group,the addition of 500 mg/kg porous zinc oxide to the diet significantly decreased the diarrhea rate(P<0.05),improve growth performance in piglets,decreased the number of Escherichia coli,Clostridium globi,and Clostridium faecalis(P<0.05)in the ileum and cecum,significantly increased the number of lactic acid bacteria(P<0.05);compared with the positive control group,dietary porous zinc oxide increased the number of lactic acid bacteria(P<0.05)in the jejunum and ileum,decreased the number of E.coli in the jejunum(P<0.05),and tended to decrease the number of E.coli in the ileum(P=0.059).In addition,compared to the negative control group,the porous zinc oxide group also significantly reduced serum D-lactic acid(P<0.05)levels and diamine oxidase(P<0.05)activity.The results showed that porous zinc oxide can significantly inhibit the growth of intestinal pathogenic bacteria,promote the proliferation of beneficial bacteria,reduce intestinal permeability,and increase intestinal health.In summary,dietary supplementation with 500-1500 mg/kg porous zinc oxide can significantly reduce diarrhea and promote growth of weaned piglets,achieving the same effect as 3000 mg/kg ordinary zinc oxide,and decreasing zinc emission.Porous zinc oxide has a specific surface area of about 20 times than that of ordinary zinc oxide,thereby increasing the probability of contact and damaging to pathogenic bacteria.Porous zinc oxide may inhibit the growth of intestinal pathogenic bacteria and regulate the structure of intestinal microflora,up-regulate the mRNA expression of tight junctions of Occludin and ZO-1 in intestinal epithelial cells,and decrease the mRNA expression of aquaporin AQP 3 in intestinal epithelial membrane,to reduce the extravasation of body fluids into the intestinal lumen,thereby relieving diarrhea in weaned piglets. |
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