| Porcine mycoplasmal pneumonia is a respiratory disease of pigs caused by infection with Mycoplasma hyopneumoniae(Mhp).Although the mortality rate of porcine mycoplasmal pneumonia is low and often ignored by farmers,it can cause a reduction in pig production performance,resulting in higher feed conversion rate,reduced daily weight gain,longer slaughter time and greatly increased rearing costs,causing significant economic losses to farmers and gradually attracting the attention of the pig breeding industry.The prevalence of Mycoplasma hyopneumoniae infection in pigs is widespread,and clinical veterinarians usually collect lungs from dead or slaughtered pigs for evaluation of lung lesions or pathogenicity testing,but there are few reports on its prevalence in largescale pig herds at home and abroad.In addition,the isolation and culture of clinical strains of Mycoplasma hyopneumoniae is difficult,and only 7 strains with published genome sequences have been studied so far,with limited research on the genetic variation of prevalent strains.Currently,vaccination is the main means of controlling Mycoplasma hyopneumoniae infection in large-scale pig farms,but commercial vaccines provide only partial protection,and the vaccine penetration rate is limited and the vaccination strategy is single in clinical practice.The eradication and purification of Mycoplasma hyopneumoniae is very difficult due to various factors,and it is important to explore effective prevention and control strategies.An agricultural company in Guangxi has 21 large-scale pig breeding farms with varying degrees of respiratory symptoms such as coughing and asthma in each herd,and Mycoplasma hyopneumoniae infection was suspected in the farms.In order to determine the prevalence and molecular epidemiological characteristics of Mycoplasma hyopneumoniae in the company’s breeding farms,to provide a theoretical basis for the prevention,control and eradication of Mycoplasma hyopneumoniae infection,and to provide prevention and control recommendations in the context of the actual pig farms,this study conducted an epidemiological investigation of Mycoplasma hyopneumoniae and an evaluation of sow vaccination effect at the end of gestation using Mycoplasma hyopneumoniae inactivated vaccine.The main results are as follows:1.Epidemiological investigation of Mycoplasma hyopneumoniaeThis study investigated the in vivo sampling method for Mycoplasma hyopneumoniae in pigs.Nasal and laryngeal swabs were collected from the same batch of gilts and the sampling performance of each was compared by real-time fluorescent quantitative PCR assay.The positive detection rate of nasal swabs was 16.67%;the positive detection rate of laryngeal swabs was 56.67%,and the Ct value was lower.The results indicated that laryngeal swab was a more appropriate sample type for epidemiological investigation of Mycoplasma hyopneumoniae in vivo.By simple random sampling,a total of 1478 laryngeal swab samples were collected from 21 fixed-point intensive breeding farms for fluorescence quantitative PCR,and the results showed the prevalence of Mycoplasma hyopneumoniae infection in pigs,with a field positive rate of 66.67%;however,the infection pressure in each farm was low,with positive rates ranging from 1.39% to 18.57%.To understand the prevalence characteristics of Mycoplasma hyopneumoniae,the samples were divided into two levels according to parity size: “0～1 parity sows” and “≥2 parity sows”,and the results showed that the positive rate of 0～1 parity sows was higher than that of ≥2 parity sows,indicating that low parity sows were more likely to be infected with Mycoplasma hyopneumoniae.12 samples from 7 of the farms were selected for molecular epidemiological analysis from the samples with positive results.The results showed that the multilocus sequence typing(MLST)of these 7 farms were all sequence type(ST)128.Sequence analysis of the conserved p36 gene and the non-conserved p97 and p146 genes showed that the genetic variation of the prevalent strains among different pig farms was small and highly homologous,providing strong evidence for the cross-farm and crossregional transmission of Mycoplasma hyopneumoniae with pig transportation.2.Evaluation of sow vaccination effect at the end of gestation using Mycoplasma hyopneumoniae inactivated vaccineBased on national and international experience with vaccination and the prevention and control of Mycoplasma hyopneumoniae,this study selected the strategy of sow vaccination at the end of gestation,and 2 positive farms with similar backgrounds were selected to evaluate the actual effect of single and double vaccination of sows at the end of gestation respectively.The results of the single vaccination showed that at farrowing,the sows had a mean antibody titer of 4433 and an antibody dispersion of 73.63%;at weaning,the sows had a mean antibody titer of 3912 and an antibody dispersion of 77.77%,and the piglets had a mean antibody titer of 672,an antibody positive rate of 25.00% and a pathogen positive rate of 18.75%.The results of the double vaccination showed that at farrowing,the sows had a mean antibody titer of 8253 and an antibody dispersion of 30.35%;at weaning,the sows had a mean antibody titer of 6707 and an antibody dispersion of 35.85%,and the piglets had a mean antibody titer of 2314,an antibody positive rate of 70.37% and a pathogen positive rate of 0.00%.This study showed that a single vaccination may not be sufficient for sows to produce high antibody levels and provide maternal immune protection for piglets;a double vaccination could maintain high antibody levels in sows during lactation and provide sufficient maternal antibodies for piglets,thus reducing the pathogen infection rate in weaned piglets.Based on the epidemiological investigation and the evaluation of the immunization effect,recommendations were given for the prevention and control of Mycoplasma hyopneumoniae,taking into account the actual situation on the pig farm. |
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