| Glycyrrhiza polysaccharide(GPS)is one of the biologically active components of licorice,which has the characteristics of immune regulation,anti-tumor,anti-oxidation,anti-virus and low cytotoxicity.As a natural plant active ingredient,it can be used as a feed additive,and it is easy to obtain at low cost and has extremely high application value.In this thesis,licorice polysaccharide is selected as the raw material to study t he effects of licorice polysaccharide on the growth performance,serum immune indexes and growth genes of weaned piglets,as well as on the related genes of porcine reproductive and respiratory syndrome virus(PRRSV)at the lung and cell level,with a view to licorice polysaccharide It provides valuable hints in the application of weaned piglets and the discovery of new anti-PRRSV natural medicines.In the experiment,90 piglets of Large White × Landrace × Duroc hybrid weaned at 28 days of age,healthy and similar in weight,were randomly divided into 5treatments,with 3 replicates for each treatment,6 piglets for each replicate,and 1 pen for each replicate.The pre-test period is 3 days and the official period is 28 days.The experimental groups were fed with GPS 400mg/kg,800mg/kg,1000mg/kg and1500mg/kg diets,and the control group was fed with basal diets.During the formal experiment,the feed intake was recorded every day.On the 1st and 28 th days,the weaned piglets with repeats(columns)were weighed on an empty stomach,and the diarrhea was checked at a fixed time every day.After the test,one weaned piglet was randomly selected in a repeat(column)for blood sampling from the anterior vena cava for the determination of serum immune indicators.After blood collection,liver,longissimus dorsi muscle and lungs were collected for subsequent determination of gene expression.In addition,Marc-145 cells were used for in vitro experiments,and GPS low,medium,and high concentration groups(10μg/mL,20μg/mL and 40μg/mL)and control groups were set up.Each group had 3 recombinants.After GPS treatment for 6 hours,the MOI was infected.=0.1 PRRSV,detect the mRNA expression of anti-PRRSV-related genes by real-time fluorescent quantitative PCR.The results showed that:(1)Compared with the control group,the 800mg/kg and 1500mg/kg GPS treatment groups increased the average daily gain(ADG)significantly(P<0.05).Compared with the control group,the 400mg/kg,800mg/kg and 1000mg/kg GPS treatment groups had significantly lower diarrhea rates(P<0.05).The serum immunoglobulin G(IgG)content in the 1000mg/kg and 1500mg/kg GPS treatment groups was significantly increased compared with the control group(P<0.05);the800mg/kg and 1500mg/kg GPS treatment groups were compared with the control group in serum The content of immunoglobulin M(Ig M)increased significantly(P<0.05).(2)Compared with the control group,the expression levels of growth hormone receptor(GHR)gene and insulin-like growth factor-2(IGF-2)gene mRNA in the different concentrations of GPS treatment group in the liver were not significantly different(P>0.05).Compared with the control group,the 800mg/kg GPS treatment group had a significant increase in insulin-like growth factor-1(IGF-1)gene mRNA expression(P<0.05).(3)Compared with the control group,the difference in GHR gene mRNA expression in the longissimus dorsi muscle treated with different concentrations of GPS was not significant(P>0.05).Compared with the control group,the 1000mg/kg GPS treatment group had a significant increase in IGF-1 gene mRNA expression(P<0.05),while the other treatment groups had no significant difference compared with the control group(P>0.05).Compared with the control group,the 800mg/kg GPS treatment group had a significant increase in insulin-like growth factor-2(IGF-2)gene mRNA expression(P<0.05),while the other treatment groups had no significant difference compared with the control group(P>0.05).(4)Compared with the control group,the expression of scavenger receptor(CD163)gene mRNA in the lungs of the GPS treatment group with different concentrations in the lungs was significantly reduced(P<0.05);compared with the control group,the 400mg/kg GPS treatment group had tissue phase Capacitive complex-7(SLA-7)gene mRNA expression increased significantly(P<0.05);Compared with the control group,the 1500mg/kg GPS treatment group had an extremely significant increase in SLA-7 gene mRNA expression(P<0.01).(5)After adding GPS to Mar-145 cells,it was found that the number of diseased cells was significantly reduced.Real-time fluorescence quantitative PCR showed that the expression of ORF7 gene mRNA was significantly reduced in the GPS-treated groups of different concentrations compared with the control group,and the expression level of ORF7 was dose-dependent.In addition,the quantitative results showed that different concentrations of GPS had a significant inhibitory effect on the PRRSV receptor CD163 gene and nuclear transcription factor κB(NF-κB)p65 gene,and had a significant promotion effect on the SLA-7 gene.In conclusion,adding GPS to the diet can improve the growth performance of weaned piglets,reduce the diarrhea rate,improve their humoral immunity and promote the expression of related growth genes.The expression of anti-PRRSV-related genes in lung and Marc-145 cells shows that GPS can resist PRRSV infection to a certain extent. |
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