| Porcine Reproductive and Respiratory Syndrome(PRRS)is a highly contagious infectious disease caused by PRRSV.Its clinical symptoms are mainly manifested as reproductive disorders in pregnant sows,increased respiratory diseases and mortality in newly born and weaned piglets,in the middle and later stages of nursery and fattening.In the early stage,the respiratory diseases of pigs increased,and the secondary infections of various bacteria were difficult to prevent and control,which had a serious impact on the development of my country’s pig industry.Vaccines and drugs are important means to reduce PRRS losses.At present,many areas have achieved stable PRRS of sow farms without obvious losses,but commercial pig herds have been in an active state of PRRSV,resulting in higher drug costs,feed-to-meat ratio,and mortality of commercial pigs.In order to help large-scale pig farms effectively improve the overall prevention and control effect of PRRS,the following researches are carried out in this paper:1.The effects of different immunization schemes on PRRSV natural infection in commercial pigsA total of 240 25-day-old piglets were divided into 3 groups with 80 pigs in each group(including 15 pigs for follow-up blood collection).Vaccine group A was inoculated with PRRS attenuated vaccine(classical strain)for the first time,and PRRS inactivated vaccine(classical strain)was inoculated for the second time;vaccine group B was only inoculated with PRRS attenuated vaccine once;the control group was injected with normal saline.The pigs in each group were weighed before the test,and the total feed consumption was recorded during the period.At the same time,the PRRSV viremia and antibody production of the experimental pigs in each group were tracked and monitored.After the test,the weight gain and feed-to-meat ratio of the experimental pigs in each group were calculated.The results showed that the test pigs were detected to be infected with PRRSV-like NADC30 strains at 44days(69 days of age)after the first vaccination.Compared with the unvaccinated control group,the test pigs were immunized once with the classic PRRS attenuated virus used in this test.The vaccine can significantly reduce the risk of viremia and the duration of viremia in pigs infected with PRRSV.On the basis of inoculation with attenuated vaccine,immunization with another dose of inactivated vaccine did not show obvious advantages.In addition,in the case of careful feeding and management,compared with the unvaccinated pigs in the control group,the pigs vaccinated with PRRS vaccine did not show a significant advantage in feed-to-meat ratio.2.Immune response analysis of piglets inoculated with PRRS attenuated vaccine at different doses and agesThe results of test 1 showed that immunization with PRRS attenuated vaccine can significantly reduce the probability of viremia and the duration of viremia after PRRSV infection in pigs.Unimmunized healthy piglets(24 6-day-old piglets,2413-day-old piglets,and 24 24-day-old piglets)were collected for PRRSV antibody(GP5 antibody)and PRRSV detection.First,they were divided into 3 groups based on the same age as the standard,and then each group was divided into 2 groups according to the principle of balanced antibody level.Groups A and B were immunized at 7 days of age,and groups C and D were immunized at 14 days of age.For immunization,groups E and F were immunized at 25 days of age.In addition,the inoculation dose per pig was 0.3 in groups A,C and E,and 0.5 in groups B,D and F.Blood was collected on the 10 th,20th,and 30 th days after immunization to monitor PRRSV GP5,N protein antibody and PRRSV viremia.The results showed that compared with the 7-day-old and 14-day-old immunized groups,the piglets in the25-day-old immunized group produced faster antibodies,and there were 5 piglets in the 7-day-old immunized group with PRRSV GP5 antibody above 1.0 that did not produce immunity after inoculation.reaction.At the same time,the overall level of N protein antibody in the 0.5 head vaccination group was higher than that in the 0.3head vaccination group,indicating that its immune effect was better.3.Evaluation of the control effect of three drugs on natural infection of fattening pigs with PRRSVPRRS vaccination cannot completely protect commercial pigs from infection,and drugs are an important auxiliary means for PRRSV prevention and control.Therefore,in this experiment,320 weaned piglets were divided into 4 groups for drug feeding test.After PRRSV infection was detected in any pig,each drug-added group immediately started to mix and add drugs.Bacteriocin and Chinese herbal medicines were fed with three drug mixtures,and the control group was fed with normal diets.The morbidity,mortality,feed-to-meat ratio,etc.were counted,and PRRSV viremia and antibody production were monitored.After the test,the weight gain and feed-to-meat ratio of pigs in each group were calculated.The results showed that the PRRSV infection began to appear in the test pigs at the age of 72 days,and the positive rate of the serum N protein antibody of the pigs in each group was 100% until the end of the experiment at the age of 111 days.The proportion of pigs with PRRSV viremia monitored was the smallest in the tylvalocin group and the Chinese herbal medicine group,which was 87%(13/15),and the duration of viremia,the pigs with viremia monitored twice or more Only the number,6 heads in the tylvanic group,was the least among the four groups.At the end of the test,compared with the control group(2.187),the tilmicosin group had the lowest ratio(2.096),and the tilmicosin group had a higher mortality rate(3.75%)than the other three groups(0%).But the difference was not significant(P>0.05).Therefore,in the control of PRRSV natural infection in this pig herd,the tilmicosin group has the best effect,followed by the selected Chinese herbal medicine group,and the tilmicosin group has no obvious effect. |
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