| Four genotypes of porcine circovirus have been found.PCV1 is non-pathogenic.PCV2 and PCV3 can cause serious clinical diseases,including post-weaning multisystem wasting syndrome(PMWS),porcine dermatitis-nephrotic syndrome(PDNS)and so on.Both can cause symptoms of slow growth in piglets and reproductive failure in sows.PCV4pathogenicity unknown.Few studies have reported how PCV3 causes slow growth in piglets,and the clinical manifestations and pathological changes of PCV3-related reproductive disorders in sows.The research content of PCV3 in this paper is mainly divided into the following two parts:1.The effect of PCV3 on the expression of growth-related hormones and growth functional genes in piglets.The aim of this study was to investigate the effect of PCV3 on the expression of growth-related hormones and functional genes in piglets,and explore the mechanism of PCV3 causing weight loss in piglets.Eight 23 day-old non-infected piglets were randomly divided into PCV3-infected group and DMEM group.Piglets of PCV3-infected and DMEM groups were intramuscular injected with 3 mL of PCV3(10~9 copies/mL)and 3 mL of DMEM in the neck respectively.The piglets were weighed before injection(0 d)and 3,7,14 and 21 d after injection,the clinical manifestations were observed,and serum,oral swab,nasal swab,anal swab were collected.Real-time quantitative PCR method was utilized to detect the viral load of PCV3;ELISA was performed to determine the content of triiodothyronine(T3)and thyroxine(T4)in the serum after infected 3d,7d,14d,21d;Real-time quantitative PCR method was utilized to determine relative expression of GHR gene,IGF-1 gene,IGF-1R gene.Pearson correlation analysis was used to analyze the correlation between daily gain and viral load in serum with content of T3 and T4 in serum and expression of growth-related functional genes in each tissue.Collectted clinical serum to detect PCV3,PCV3-Cap antibody and its thyroid hormone concentration.Statistical average daily gain and final weight finding that in the PCV3-infected group were significantly lower than those in the DMEM group(P<0.01).The viral load of serum,oral swab,nasal swab and anal swab in infected group reached the highest at 14d.The content of T3 in the infected group was extremely significantly higher than that in DMEM group on the 14th and 21st day of infection(P<0.01),and there was no significantly difference in the content of T4(P>0.05).Compared with DMEM group,the relative expression of IGF-1 gene in longissimus dorsi was extremely significantly decreased(P<0.01),there was no significant difference in the relative expression of GHR,IGF-1 and IGF-1R genes in leg muscle and spleen(P<0.05),the relative expression of GHR gene in liver was extremely significantly increased(P<0.01),and the relative expression of IGF-1R gene was increased significantly(P<0.05).The test results of T3 and T4 concentrations in clinical pig serum showed that when PCV3 antibody was positive,the content of T3 in serum showed a very significantly decrease(P<0.01),and the content of T4 was not significant(P>0.05).When both antibody and antigen were positive,the content of T3showed a very significantly increase(P<0.01).The correlation analysis results of piglets daily gain and viral load with the content of T3 and T4,and the expression of growth-related functional genes are as follows.The daily gain of piglets was significantly negatively correlated with content of T3(P<0.01),and the viral load was positively correlated with content of T3(P<0.01).Daily gain and viral load had no significant correlation with content of T4(P>0.05).In the longissimus dorsi,there were no significant correlations between GHR and IGF-1R genes with daily gain and viral load of piglets(P>0.05);IGF-1 gene was positively correlated with daily gain(P<0.01),and negatively correlated with viral load(P<0.01).In leg muscle and spleen,GHR,IGF-1,IGF-1R genes had no significant correlation with daily gain and viral load of piglets(P>0.05).In the liver,GHR and IGF-1R genes were significantly negatively correlated with daily gain of piglets(P<0.01);GHR,IGF-1R genes were significantly positively correlated with viral load(P<0.01);IGF-1 gene had no significant correlation with piglets daily gain and viral load(P>0.05).The results of the investigation of content of T3 and T4 in clinical serum are as follows.When only PCV3 antibody was positive,the content of T3 in serum showed a very significant decrease(P<0.01).When both the nucleic acid and antibody levels of PCV3were positive,the content of T3 showed a very significant increase(P<0.01);the difference of T4 concentration was not significant(P>0.05).When both the nucleic acid and antibody levels of PCV3 were positive,the content of T3 showed a very significant increase(P<0.01).There was no significant difference in T4 concentration(P>0.05).The correlation analysis results of PCV3 load,PCV3-Cap antibody level with the content of T3 and T4 in clinical serum are as follows.The content of T3 had a significantly positively correlated with viral load(P<0.01),no correlated with antibody level(P>0.05).There was no correlation between the content of T4 with viral load and antibody level(P>0.05).In summary.During the infection of piglets with PCV3,the thyroid function will be disturbed.Causes the body’s hyperthyroidism or hypothyroidism,causing the body’s catabolism disorder of carbohydrates,lipids and proteins,etc.Decreased growth-promoting and mitogenic effects of the IGF-1 gene on the longissimus dorsi resulted in stunted growth and lower daily gain in piglets.2.Diagnosis and treatment of PCV3-related reproductive disorders in sows.Between August and December 2020,the sows after breeding had regular return to estrus in a pig farm with 220 sows in Hubei.The conception rate is about 10%.The farrowing situation of the sows after successful mating was recorded.The 43 pregnant sows with an average of 6-7 piglets per litter,and 70%of the piglets were trembling at about seven days of age.In this study,the content of Aflatoxin B1 was detected by collecting the feed in the feed trough of the sows,meanwhile,the oral and anal swabs and serum of the sows were collected.In addition,13 sows were dissected randomly and collectted their spleen,lymph nodes,spinal cord,uterus,ovary to detected the virus.Observation of pathological changes of sow ovary.The detection results were summarized and analyzed to diagnose the reasons for the low conception rate and continuous return to estrus of the sows in this farm.The content of aflatoxin B1 in the feed brought back from the pig farm is within the allowable range(<20μg/kg,).PCR and RT-PCR methods were used to detected PCV2,PCV3,PRV,PPV,PRRSV,CSFV.the results of oral and anal swabs and serum were all negative.The virus detection results in 13 sows are as follows.The positive rate of PCV2was 69.23%(9/13),the positive rate of PCV3 was 38.46%(5/13),the co-infection positive rate of PCV2 and PCV3 was 30.76%(4/13).The PCV2 and PCV3 loads in each tissue were detected by qPCR.It was found that PCV2 was the highest in the spinal cord,followed by the spleen,and the least in the ovary;PCV3 was the highest in the spleen,followed by the lymph nodes,and the least in the uterus.Analysis of ORF2 gene sequences in PCV2 and PCV3 positive samples found that PCV2 was subtype 2d,PCV3 was subtype 3a.Observation of ovarian pathological section found that congestion.The follicular is irregularly shaped and flat.Low number of follicle cells.After diagnosis,it was determined that the main reason for the continuous return to estrus of the sows in this farm was co-infection with PCV2 and PCV3.Sequencing analysis found that PCV2 was subtype 2d and PCV3 was subtype 3a.According to the diagnosis results and the situation of the farm,all of the sows were vaccinated with PCV2 vaccine,meanwhile,the whole farm was sterilized by atomization to strengthen biosafety prevention.Eventually,the farm returned to normal production. |
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