| Porcine epidemic diarrhea(PED)is an intestinal infectious disease with high mortality in suckling piglets.especially in piglets born of sows with low antibody levels are more severe because they cannot obtain higher maternal antibodies from the colostrum of sows.At present,there is no effective treatment plan for PED..Vaccination is a common prevention and control method for PED,but the situation of each pig farm is different.Appropriate immunization program is usually one of the important factors for successful prevention and control of PED in pig farms.This study examined the correlation of antibody levels between prenatal and postnatal in sows to predict sows that would be likely to have low antibody levels at litter.And then,identify epidemic strains in pig farms,select strains of the vaccine that are more closely related and vaccines that have better immune responses,to explore the best PED immunization program to improve the antibody level of sows with low antibody level and provide evidence for the prevention and control of PED in pig farms.1.Correlation between prenatal and postpartum antibody levels of sowsAt present,there are various of PEDV-IgA ELISA kits for sow colostrum in the market,with different detection results.Therefore,three commercial ELISA kits commonly used in the market were selected to detect and compare the antibody levels of the same batch of colostrum samples.The results showed that kit A(imported reagent)and kit B(domestic reagent)had a high correlation(r=0.888),and the correlation between kit C(imported reagent)and kit A、B was low(r< 0.05).Then,the blood,anal swabs and colostrum were collected from 68 sows at the 50 prenatal days and on the day of production,serum and colostrum PEDV antibody levels were detected at the same time.The results showed that although sows were inoculated with one live and one inactivated PEDV vaccine at 45 and 20 days before the production,there was still a positive correlation between serum Ig G level of sows at50 prenatal days the production and puerperal colostrum Ig G antibody level(r=0.59),and a weak positive correlation between serum Ig G level of sows at 50 prenatal days the production and IgA antibody level of sows at colostrum(r =0.35).2.Screening of PEDV vaccine and study of immunization programIn the past,the maternal antibody level of 0 parities sows in pig farms was generally low.In order to explore better immunization schemes and improve the maternal antibody level of such sows,so as to achieve the purpose of protecting piglets.Firstly,PEDV epidemic strains in pig farms where the experiment was conducted were investigated and analyzed in this study,and attenuated vaccine(vaccine C)with closer genetic relationship to epidemic strains was selected.Then,a total of 200 gilts were immunized with different immunization procedures by using the vaccines originally used in pig farms(attenuated vaccine A,inactivated vaccine B),the vaccines selected in this study and the self-made inactivated vaccine D.Finally blood samples were collected after the first immunization and the second immunization to detect antibody production.The results of pandemic strain analysis showed that the pandemic strain in this pig farm was PEDV variant strain,and the first and second immunization combined with vaccine C and vaccine B had the best effect.After the first immunization,the S/P value of serum Ig G antibody of PEDV reached 2.89,and the variation coefficient was 27.5%.After the second immunization,the S/P value of Ig G antibody reached 3.06,the coefficient of variation was only18.25%.3.Adjustment of prenatal PEDV immunization program for sows with low antibody levelsIn this experiment,blood samples were collected from the anterior vena cava of0 parities sows in prenatal 50 days,its serum PEDV-Ig G antibody was detected,and sows with low antibody level were screened out.After that,combined with the correlation between serum Ig G level of sows at prenatal 50 days and Ig G antibody level of sows at colostrum after production,50 sows with low antibody level at production were estimated as experimental pigs.Then the 50 sows were divided into the experimental group and the control group according to the antibody level,combined with the results of different immunization procedures in the second experiment,and selected the best immunization program.The sows in the experimental group were inoculated with attenuated vaccine B and inactivated vaccine C simultaneously at 45 prenatal days and 20 prenatal days,while the sows in the control group were inoculated by the farm according to the enhanced immunization program.Finally,serum and colostrum of sows were collected after delivery to detect PEDV antibodies.The results showed that compared to control groups receiving five prenatal PEDV vaccination in sows,sows in the experimental group also produced the same level of serum Ig G antibody(mean S/P value 3.52),colostrum Ig G antibody(mean S/P value 3.03)and IgA antibody(mean PP value0.96). |
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