| Porcine viral diarrhea is becoming more and more prevalent in China,causing huge economic losses to the pig industry.Porcine viral diarrhoea includes porcine epidemic diarrhoea（PED）,porcine infectious gastroenteritis and porcine rotavirus disease,with PED being the most serious.PED is an acute,highly contagious intestinal disease caused by Porcine epidemic diarrhea virus（PEDV）with typical symptoms of diarrhoea,vomiting,late dehydration and death.Pigs at all stages of growth can be infected with PEDV,but the clinical signs of infection vary.The mortality rate of lactating piglets infected with PEDV can be as high as 100%,while the mortality rate of adult pigs infected with PEDV is low and the clinical signs of infection are mild.The development of PED is related to many factors such as the pig organism,feeding management,immunisation,biosecurity and the emergence of new mutant strains of the virus.In general,vaccination is effective in raising antibody levels in pigs.However,PEDV is a large genomic RNA virus that is susceptible to nucleic acid mutations and has many subtypes,making vaccination against porcine epidemic diarrhoea ineffective.In this study,by sampling four pig farms in different areas of a farming company in Hebei Province,detecting the pathogen by PCR technology and analysing the prevalent strains of epidemic diarrhoea in pig farms through gene sequencing;evaluating the immunization effect and further conducting domestication immunization trials with strong strains,finally providing effective prevention and control solutions for the prevention and control of PED in pig farms in order to reduce the incidence of the disease and provide technical guidance for the prevention and control of PED in the pig farming industry.In this study,manure was collected from four pig farms of a breeding company in Hebei Province,identified by PCR and sequenced for gene sequence analysis of PEDV isolates.The test results were as follows: 20.00% positive for field A and 99.1% homology with AJ1102 and 97.4% homology with NHTa-2020 for the gene assay.The B-field positivity rate was93.33% and the gene assay showed 97.3-97.5% homology with S-INDEL,95.2%-95.4%homology with AJ1102 and 95.8%-96.0% homology with NHTa-2020.The C-field positivity rate was 91.11% and the gene assay showed 98.8% homology with the PLK isolate and97.4% homology with AJ1102.The D-field positivity rate was 62.22% and the gene assay showed 99.1% homology with NHTa-2020 and 96.5% homology with AJ1102.The pigs in this study were immunised with three general PED vaccinations per year and a follow up vaccination 3 weeks before farrowing.Thirty sows were randomly selected from each of the four farms and their milk was collected at day 7 of farrowing for the determination of Immunoglobulin A（IgA）in milk.The results showed that among the four farms,farm A had the best immunization effect,with IgA antibody levels in milk reaching 95.00%;farms B,C and D had relatively poor immunization effect,with IgA antibody levels in milk at 58.33%,35.00% and 13.33% respectively.A domestication trial with a strong strain was determined to assess the effect of domestication immunity.A total of 90 milk samples were collected from 30 sows on the 3rd,7th and 14 th d after farrowing.The results showed that the level of IgA antibodies in the milk of domesticated sows was significantly higher,and the level of IgA antibodies in the milk 14 d after farrowing remained high.The highest levels of IgA antibodies were found in milk domesticated for 2 times.In descending order according to IgA antibody levels: domesticated2 times > domesticated 1 time > undomesticated.In summary,the gene sequence analysis of the different prevalent strains in the pig farms showed 99.1% homology with AJ1102 in farm A,97.3%-97.5% homology with S-INDEL in farm B,98.8% homology with PLK isolate in farm C and 99.1% homology with NHTa-2020 in farm D.The results of monitoring IgA antibody levels in sow milk showed that farm A had the best immunization effect,indicating that choosing a vaccine strain consistent with the prevalent strain could achieve a better control effect.At the same time,domesticated immunisation with a strong strain of vaccine can significantly enhance the effectiveness of immunisation.Therefore,it is important that pig farms firstly carry out an epidemic strain determination,secondly select the strain and domesticate it,and finally combine it with a reasonable immunisation programme in order to prevent and control PED more effectively. |
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