An assessment of the duration of Mycoplasma hyopneumoniae infection in an experimentally infected population of pigs

Mycoplasma hyopneumoniae (M. hyopneumoniae) is the primary pathogen of enzootic pneumonia (EP), a highly prevalent respiratory disease that affects pigs worldwide. Previous studies have demonstrated that M. hyopneumoniae infection can be longer than 185 days; however, the total duration of infection has not been determined yet. Therefore, the objective of this study was to determine the duration of M. hyopneumoniae infection in asymptomatic carriers. To achieve our goal, 60 pigs were inoculated with M. hyopneumoniae strain 232 and the persistence of M. hyopneumoniae in the respiratory tract was assessed by detection of the bacterial DNA in bronchial swabs and the ability of the infected pigs to transmit the pathogen to sentinels. Infection of the inoculated animals was demonstrated by the detection of M. hyopneumoniae DNA in nasal swabs, seroconversion to the bacteria and the onset of dry coughing. Experimentally infected pigs shed M. hyopneumoniae prior to and after the cough was observed. M. hyopneumoniae DNA was detected in 100% of experimentally infected pigs at 94 days post infection (dpi), 61% at 214dpi and 0% at 254dpi. Experimentally infected pigs transmitted the bacteria to sentinels at 80 and 200dpi. Results of this study have demonstrated that M. hyopneumoniae infected pigs can be incubatory as well as convalescent carriers of the pathogen and that convalescent carriers can remain infectious for up to 200 days. Total clearance of M. hyopneumoniae in the group was evidenced, demonstrating that duration of M. hyopneumoniae infection lasts less than 254 days.     

Evaluation of virulence of Mycoplasma hyopneumoniae field isolates

The course of enzootic pneumonia, caused by Mycoplasma hyopneumoniae, is strongly influenced by management and housing conditions. Other factors, including differences in virulence between M. hyopneumoniae strains, may also be involved. The aim of this study was to evaluate the virulence of six M. hyopneumoniae field isolates and link it to genetic differences as determined by randomly amplified polymorphic DNA (RAPD) analysis. Ninety, conventional M. hyopneumoniae-free piglets were inoculated intratracheally with the field isolates, a virulent reference strain or sterile culture medium. Animals were examined daily for the presence of disease signs and a respiratory disease score (RDS) was assessed per pig. Twenty-eight days post infection, pigs were euthanized, blood sampled and a lung lesion score was given. Lung samples were processed for histopathology, immunofluorescence testing for M. hyopneumoniae and isolation of M. hyopneumoniae. RAPD analysis was performed on all M. hyopneumoniae strains. Significant differences between isolates were found for the RDS, lung lesion score, histopathology, immunofluorescence and serology. Based on the results of the different parameters, isolates were divided into three "virulence" groups: low, moderately and highly virulent strains. Typically, a 5000 bp RAPD fragment was associated with the highly and moderately virulent strains whereas it was absent in low virulent strains. It was concluded that high variation in virulence exists between M. hyopneumoniae strains isolated from different swine herds. Further studies are required to determine whether the 5000 bp fragment obtained in the RAPD analysis can be used as a virulence marker.     

Experimental dual infection of pigs with an H1N1 swine influenza virus (A/Sw/Hok/2/81) and Mycoplasma hyopneumoniae

Dual infection of pigs with swine influenza virus (SIV) and Mycoplasma hyopneumoniae was carried out to compare the clinical and pathological effects of dual infection in caesarian derived and colostrums deprived (CDCD) pigs, with that of a single infection with M. hyopneumoniae. In Experiment 1, 40-day-old CDCD pigs were inoculated only with SIV (A/Sw/Hok/2/81, H1N1). The virus was isolated from nasal swabs for 5-6 days. None of these pigs showed clinical signs of infection throughout the experimental period. These results suggested that this strain can infect pigs but is only slightly pathogenic when it is inoculated singly to a CDCD pig. In Experiment 2, 60-day-old CDCD pigs were inoculated with M. hyopneumoniae and then were inoculated with SIV (A/Sw/Hok/2/81) at 1 week (MHYO-7d-SIV-7d group) or 3 weeks (MHYO-21d-SIV-7d group) after M. hyopneumoniae inoculation. Macroscopically, dark red-to-purple lung lesions were observed in all of pigs at 14 or 28 days post-inoculation. Percentages of dark red-to-purple lung lesions in dual infection groups (MHYO-7d-SIV-7d group: 18.7 +/- 4.2%, MHYO-21d-SIV-7d group: 23.0 +/- 8.0%) were significantly (P < 0.05) increased compared to those of each control group in which pigs were inoculated only with M. hyopneumoniae (MHYO-14d group: 4.7 +/- 2.9%, MHYO-28 group: 3.3 +/- 2.4%). Microscopically, bronchial epithelial lesions (epithelial disruption, degeneration, hyperplasia and formation of microabscess) were frequently observed in dark red-to-purple lung lesions of only the dual infection groups. These results demonstrate that the lung lesion of pigs inoculated with M. hyopneumoniae and SIV is more severe than that of pigs inoculated only with M. hyopneumoniae.     

Mycoplasma hyopneumoniae increases the susceptibility of pigs to experimental Pasteurella multocida pneumonia.

The interaction between Mycoplasma hyopneumoniae and Pasteurella multocida in experimental pneumonia was investigated in conventional pigs. The experimental animals were 49 days old when inoculated with M. hyopneumoniae; they were inoculated with P. multocida after 23 days, and killed 13 days later. In pigs inoculated only with P. multocida, clinical signs and lung lesions were not observed, and the agent was not recovered. Pigs inoculated with M. hyopneumoniae developed fever, moderate cough and dyspnea which tended to disappear, and small proliferative lung lesions from which M. hyopneumoniae was isolated. Pigs inoculated with both agents had higher fever, severe cough and dyspnea which tended to aggravate, and extensive exudative lung lesions from which organisms were isolated. All animals had similar growth rates, but the group infected with both agents consumed 60% more food. Therefore, M. hyopneumoniae causes mild pneumonia, whereas P. multocida is not pathogenic alone but aggravates the pneumonia initiated by M. hyopneumoniae.     

Evaluation of tulathromycin for the treatment of pneumonia following experimental infection of swine with Mycoplasma hyopneumoniae

Tulathromycin was evaluated in the treatment of pneumonia in weaned pigs inoculated intranasally with Mycoplasma hyopneumoniae. Five days postchallenge, the pigs were randomized to treatment with a single IM administration of saline, a single IM administration of tulathromycin (2.5 mg/kg; day 0), or three IM administrations of enrofloxacin (5.0 mg/kg; days 0, 1, 2). Pigs were necropsied on day 12 or 13. Unchallenged controls remained healthy with no lung pathology. Compared with saline, coughing, mean lung lesion score, and proportional lung weight were significantly reduced and weight gain was significantly greater for tulathromycin-treated pigs (P < .05). Compared with enrofloxacin, there were no significant differences in proportional lung weight or weight gains, but coughing and lung lesion scores were greater for tulathromycin-treated pigs (P < .05). Tulathromycin was effective in the treatment of pneumonia following experimental infection with M. hyopneumoniae.     

Experimental reproduction of postweaning multisystemic wasting syndrome in pigs by dual infection with Mycoplasma hyopneumoniae and porcine circovirus type 2

The objectives of this study were to investigate the interactions between Mycoplasma hyopneumoniae and porcine circovirus type 2 (PCV2) and to establish a model for studying the pathogenesis of and testing intervention strategies for the control of PCV2-associated porcine respiratory disease complex (PRDC). Sixty-seven pigs were randomly assigned to four groups. Group 1 (n=17) pigs served as controls, group 2 (n=17) pigs were inoculated with M. hyopneumoniae, group 3 (n=17) pigs were dual infected with M. hyopneumoniae and PCV2, and group 4 (n=16) pigs were inoculated with PCV2. Pigs were inoculated intratracheally with M. hyopneumoniae at 4 weeks of age followed by intranasal inoculation with PCV2 at 6 weeks of age. Dual-infected pigs had moderate dyspnea, lethargy, and reduced weight gain. The overall severity of macroscopic lung lesions, PCV2-associated microscopic lesions in lung and lymphoid tissues, and the amount of PCV2-antigen associated with these lesions were significantly (P <0.05) higher in dual-infected pigs compared with all other groups. Four of 17 (23.5%) dual-infected pigs had decreased growth rate and severe lymphoid depletion and granulomatous lymphadenitis associated with high amounts of PCV2-antigen consistent with postweaning multisystemic wasting syndrome (PMWS). PCV2-antigen in lung tissue was most often associated with M. hyopneumoniae-induced peribronchial lymphoid hyperplasia, suggesting that this is an important site for PCV2 replication in the lung. This study indicates that M. hyopneumoniae potentiates the severity of PCV2-associated lung and lymphoid lesions, increases the amount and prolongs the presence of PCV2-antigen, and increases the incidence of PMWS in pigs.     

Infection dynamics of porcine reproductive and respiratory syndrome virus in a continuous-flow population of pigs also infected with Mycoplasma hyopneumoniae

Twenty-eight 10-week-old pigs were inoculated intratracheally with 1 x 10(5) colour-changing units/ml Mycoplasma hyopneumoniae strain 232, and another 32 pigs were not inoculated but were divided into 12 direct-contact pigs and 20 indirect-contact pigs. Thirty-five days later, the inoculated pigs were inoculated intranasally with 1 x 10(2.4) tcid50 of porcine reproductive and respiratory syndrome virus (PRRSV) strain mn 30-100. Viraemia, seroconversion and the transmission of PRRSV in the M hyopneumoniae-infected pigs were then assessed for four months. Three groups of 10 age-matched gilts were introduced as sentinels into the experimental barn on days 28, 56 and 84 after the PRRSV infection. The persistence of PRRSV was evaluated in both the experimentally and naturally infected pigs, which were slaughtered 120, 135 and 150 days after the infection. The period of viraemia and the extent of seroconversion were similar to those observed in studies of pigs infected only with PRRSV, suggesting that under the conditions of the study M hyopneumoniae did not affect these features of the disease. A delayed pattern in the seroconversion and proportion of pcr-positive pigs was observed in the direct and indirect contact groups, and the persistence of PRRSV in tissues was confirmed by pcr at 120 and 150 days after infection only in the directly inoculated pigs and not in the direct- or indirect-contact groups of pigs.     

Evaluation of the aerosol transmission of a mixed infection of Mycoplasma hyopneumoniae and porcine reproductive and respiratory syndrome virus

To evaluate the transmission of Mycoplasma hyopneumoniae and porcine reproductive and respiratory syndrome virus (PRRSV) by aerosol as either a single or mixed infection, 28 pigs were inoculated intratracheally with M hyopneumoniae on day 0 and infected intranasally with PRRSV on day 35; they were housed together in a barn. To assess the aerosol transmission of M hyopneumoniae as a single infection, one trailer (A) containing 10 five-week-old sentinel pigs was placed along the south side of the infected barn (1 m from the fans) on day 28. To assess the mixed infection, two trailers (B and C), each containing 10 five-week-old sentinel pigs, were placed along each side of the barn on day 42. The sentinel pigs in the three trailers were exposed to the exhaust from the fans for seven days. No M hyopneumoniae infection was detected in the sentinel pigs in trailer A, but it was detected in the sentinel pigs in trailers B and C. No PRRSV was detected in any of the sentinel pigs.     

Swine Enzootic Pneumonia: Age Susceptibility and Treatment Schemata

Pigs were found to be susceptible to Mycoplasma hyopneumoniae-induced swine enzootic pneumonia (SEP) when four hours old. Chlortetracycline was incapable of preventing transmission of SEP from infected pigs on the drug to susceptible, untreated pigs. When continuous medication was started at one or two weeks postinoculation, chlortetracycline partially or completely inhibited formation of SEP lesions but did not clear M. hyopneumoniae from inoculated pigs. Chlortetracycline administered orally was capable of completely suppressing the formation of SEP lesions in inoculated pigs if given prophylactically and if milk was withheld for several hours after each treatment; lesion suppression was incomplete if milk was given ad libitum. In either case treated animals remained infected with M. hyopneumoniae.     

Effect of Mycoplasma hyopneumoniae colonization at weaning on disease severity in growing pigs

To determine whether Mycoplasma hyopneumoniae colonization at weaning in off-site weaning systems is associated with the severity of respiratory disease due to this agent in growing pigs, we studied 20 groups, each group representing a different week in production, in sow herds at 3 farms of 3000 sows each that had a prevalence of M. hyopneumoniae colonization at weaning higher than 5%. The calculated sample size for assessment at weaning was 39 piglets for each group under study; 39 litters were randomly selected, and 1 piglet was randomly selected from each litter for testing and ear-tagged. In total, 780 piglets were tested. The presence of M. hyopneumoniae in nasal swabs at weaning was established by nested polymerase chain reaction (PCR). All groups were followed until slaughter, at which time blood samples were collected from each ear-tagged pig to test for M. hyopneumoniae antibodies, bronchial swabs were collected for detection of M. hyopneumoniae DNA by nested PCR, and the lung lesion score and percentage of affected lungs in the same animals were calculated. Correlation analyses showed a positive correlation between colonization at weaning and all 4 dependent variables indicating infection at slaughter: average lung lesion score, percentage of affected lungs, presence of M. hyopneumoniae on the bronchial epithelium, and seroconversion. This study provides evidence that severity of the disease can be predicted by the prevalence at weaning in segregated systems. Therefore, strategies focused on reducing colonization at weaning seem to be important elements in the global control of M. hyopneumoniae in segregated production systems.     

Evaluation of the ELISA and comparison to the complement fixation test and radial immunodiffusion enzyme assay for detection of antibodies against Mycoplasma hyopneumoniae in swine serum

An enzyme-linked immunosorbent assay (ELISA) was evaluated for detection of antibodies (Ab) against Mycoplasma hyopneumoniae and M. flocculare in sera from swine experimentally infected with these agents. In addition, the ELISA was compared with the complement fixation test (CFT), and radial immunodiffusion enzyme assay (RIDEA) for the demonstration of Ab against M. hyopneumoniae. Twenty two 6-week-old swine from a respiratory disease-free herd were divided into five groups. Two or three pigs from each of the four groups were inoculated, respectively, with M. hyopneumoniae or with M. flocculare while two pigs in each group were contact exposed to the inoculated penmates. A fifth group, consisting of three pigs, served as inoculated controls. Pigs inoculated with M. hyopneumoniae began coughing 13 days post inoculation (PI). Antibodies were first detected 2 weeks PI with the CFT, 3 weeks PI with the ELISA, and 5 weeks PI with the RIDEA. With the ELISA and RIDEA, Ab were still detectable one year PI at a very low level. With the CFT, Ab were not detectable in sera from any swine beyond 5 months PI. At necropsy 1 year PI, no lesions were detected in lungs of any of the animals nor were mycoplasmas detected. M. flocculare inoculated or contact-exposed pigs never evidenced clinical signs. Antibodies against M. flocculare were first detected 5 to 12 weeks PI with CFT, and 6 to 12 weeks PI with the ELISA. Peak optical density (OD) values obtained in the ELISA with M. flocculare Ab were as high as the values obtained with peak M. hyopneumoniae Ab titers. Levels of Ab against M. flocculare were at relatively higher OD at 1 year PI than Ab against M. hyopneumoniae. Sera with high levels of Ab against M. flocculare cross-reacted slightly with M. hyopneumoniae antigen in immunoblotting and ELISA.     

两种灭活方法制备的猪肺炎支原体灭活疫苗的免疫效果比较

为对比使用甲醛、二乙烯亚胺（BEI）两种灭活方法制备的猪肺炎支原体灭活疫苗对猪的呼吸道发病率、肺部病变记分、饲料转化率、日增重、以及猪血清抗体水平等指标的影响,将120头健康仔猪随机分成三个试验组和一个对照组,于7、21日龄对试验组的仔猪进行疫苗接种,所有猪于20、50、80及140日龄采血分离血清,检测血清中猪肺炎支原体抗体水平。结果显示,用BEI灭活的疫苗在呼吸道发病率、肺部病变记分、饲料转化率、日增重、以及猪血清抗体水平等各项指标均好于甲醛灭活的疫苗（P<0.05）,与进口疫苗无显著差异。试验表明,使用BEI灭活方法制备的猪肺炎支原体灭活疫苗的免疫效果好。     

Effectiveness of treatment with lincomycin hydrochloride and/or vaccination against Mycoplasma hyopneumoniae for controlling chronic respiratory disease in a herd of pigs

A herd of pigs infected with Mycoplasma hyopneumoniae was used in a double-blind randomised trial to assess the effectiveness of three control strategies against chronic respiratory disease in growing-finishing pigs. One group of 61 pigs received 220 ppm lincomycin hydrochloride in the feed from day 71 to day 91, a second group was vaccinated against M. hyopneumoniae at four and 28 days of age, and a third group received both treatments; a fourth group was left untreated as a control. Throughout the nursery-finishing period (day 29 to slaughter) the average daily weight gain and feed conversion rate of all the treated groups were slightly better than in the controls, but there were no significant differences between them. There were no significant differences between the treated groups in terms of clinical signs, serology, pathology or mortality, which was very low throughout the trial.     

Detection of Mycoplasma hyopneumoniae in lung and nasal swab samples from pigs by nested PCR and culture methods

We examined nasal swab and lung homogenate samples collected from pigs experimentally and naturally infected with Mycoplasma hyopneumoniae for the detection of M. hyopneumoniae by the nested PCR (nPCR) and culture methods. In the 23 experimentally infected pigs, M. hyopneumoniae was commonly detected in nasal swabs by the nPCR and culture methods at 4 weeks after inoculation, and there was a significant correlation (P<0.01) between the titers of viable organisms in nasal swabs and in lung homogenates in the experimentally inoculated pigs. In the naturally infected pigs, on the other hand, discrepancies in detection were found between nasal swab and lung homogenate samples in 17 of 36 cases, although the presence of gross lung lesions correlated relatively well with the detection of organisms from the samples. Our results indicated that the diagnosis of mycoplasmal pneumonia by nPCR in individual pigs with nasal swabs is reliable under these experimental conditions. At present, nPCR with nasal swabs should only be used for monitoring the disease status at the herd level under field conditions.     

Detection of respiratory pathogens in air samples from acutely infected pigs

Pathogens causing significant respiratory disease in growing pigs include Porcine reproductive and respiratory syndrome virus, Porcine circovirus 2, swine influenza virus, porcine respiratory coronavirus, Mycoplasma hyopneumoniae, and Bordetella bronchiseptica. The objective of this research was to characterize the respiratory excretion of these pathogens by acutely infected pigs. Pigs were inoculated under experimental conditions with 1 pathogen. Samples were collected from the upper respiratory tract and exhaled air. All pathogens were detected in swabs of the upper respiratory tract, but only M. hyopneumoniae and B. bronchiseptica were detected in expired air from individually sampled, acutely infected pigs. These findings suggest either that the acutely infected pigs did not aerosolize the viruses or that the quantity of virus excreted was below the detection threshold of current sampling or assay systems, or both, at the individual-pig level.     

Evaluation of local and systemic immune responses induced by intramuscular injection of a Mycoplasma hyopneumoniae bacterin to pigs

OBJECTIVE: To evaluate immune responses induced by administration of Mycoplasma hyopneumoniae bacterin to pigs. Animals-60 healthy 7- to 10-day-old cross-bred boars. PROCEDURE: Pigs were assigned to 1 of 4 pig groups (15 pigs/group): vaccinated, challenged; vaccinated, nonchallenged; nonvaccinated, challenged; nonvaccinated, nonchallenged. Vaccinated pigs received IM injections of a mycoplasma bacterin on days 0 and 14, whereas nonvaccinated pigs received saline (0.9% NaCl) solution. Pigs in the challenged groups were inoculated intratracheally with M hyopneumoniae on day 42. Pigs were euthanatized and necropsied 41, 44, 48, and 70 days after the first vaccination, and proportion of lung surface with pneumonic lesions was determined. Percentage of lymphocyte subpopulations and number of interferon-gamma (IFN-gamma) secreting lymphocytes in blood and tissues, cytokine and antibody concentrations in bronchoalveolar lavage (BAL) fluid, and serum antibody concentrations were determined. RESULTS: Vaccination against and infection with M hyopneumoniae induced a local mucosal immune response in the respiratory tract of pigs. Proportion of lung surface with pneumonic lesions in vaccinated challenged pigs was reduced on day 70, compared with nonvaccinated challenged pigs. Vaccination stimulated the production of M hyopneumoniae-specific IFN-gamma secreting blood lymphocytes. Tumor necrosis factor-alpha concentration in BAL fluid on day 70 was increased in nonvaccinated challenged pigs, compared with vaccinated challenged pigs. CONCLUSIONS AND CLINICAL RELEVANCE: Vaccination against M hyopneumoniae induced local, mucosal, humoral, and cellular immune responses. Moreover, vaccination reduced the severity of lung lesions in challenged pigs, suggesting that mucosal antibodies, mediation of the inflammatory response, and cell-mediated immune responses are important for control of mycoplasmal pneumonia in pigs.     

Evaluation of tiamulin for treatment of mycoplasmal pneumonia in swine

During 3 trials, using affected pigs of various ages, tiamulin was evaluated for treatment of experimentally induced mycoplasmal pneumonia. Pneumonia was induced in respiratory tract disease-free swine by intratracheal inoculation of a lung homogenate containing Mycoplasma hyopneumoniae. Eleven days after inoculation, when more than 20% of pigs were coughing, pigs were allotted to 3 or 4 groups (n = 8 pigs each) and were given regimens of no medication or 60 mg, 120 mg, or 180 mg of tiamulin/L of drinking water for 10 days. Twenty-one days after cessation of medication, pigs were euthanatized and then were necropsied. Results obtained from the 3 trials did not indicate significant difference among treatment groups in severity of macroscopic or microscopic lesions induced by M hyopneumoniae or in detection of M hyopneumoniae by use of immunofluorescent technique. Clinical evaluations, daily gain, and feed efficiency did not differ significantly among treatment groups. In this study, tiamulin administration did not have beneficial effects in swine with mycoplasmal pneumonia.     

Histochemical and morphologic changes of porcine airway epithelial cells in response to infection with Mycoplasma hyopneumoniae.

Mycoplasma hyopneumoniae causes pneumonia in pigs. The effect of infection by this organism on histochemical characteristics of airway mucin within epithelial cells was studied. Seven- to 10-week-old pigs were inoculated intratracheally with M hyopneumoniae or culture broth, and lung tissues were collected from inoculated and control pigs at 2, 4, and 6 weeks after inoculation. Tissue sections were stained with periodic acid-Schiff/Alcian blue, pH 2.5 or high iron diamine/Alcian blue. Histologic features of randomly selected bronchi, bronchioles, and submucosal glands were compared in sections stained with periodic acid-Schiff/Alcian blue. Bronchial goblet cell sulfomucin and sialomucin were quantitated by image analysis of sections stained with high iron diamine/Alcian blue. Bronchi and bronchioles of infected pigs contained proportionately fewer goblet cells with mucin at all stages of infection than age-matched control pigs. Goblet cells in bronchi of infected pigs contained significantly less total mucin and sialomucin, and significantly more sulfomucin than goblet cells of control pigs. Increased sulfated mucin in bronchial goblet cells may reflect altered glycoprotein production or secretion in response to infection with M hyopneumoniae.     

Serum and mucosal antibody responses and protection in pigs vaccinated against Mycoplasma hyopneumoniae with vaccines containing a denatured membrane antigen pool and adjuvant

Objective To investigate the protective efficacy of a pool of denatured membrane protein antigens of Mycoplasma hyopneumoniae (J strain) in the molecular size range 70 to 85 kDa (F3 antigen) in combination with adjuvants for pigs challenged with M hyopneumoniae .
Design A vaccine efficacy experiment with assessment of serum and respiratory tract antibody responses.
Procedure F3 antigens were emulsified with five different adjuvants. To groups of three pigs per vaccine, four vaccines were given by intramuscular injection, and two vaccines, including one of those given intramuscularly, were given by intraperitoneal injection.
Results Compared to six unvaccinated pigs, animals vaccinated with F3 antigen displayed significantly reduced pneumonia (54% reduction in mean lung score) following experimental challenge. Analysis of post-vaccination, pre-challenge IgG and IgA ELISA antibody absorbances in serum and respiratory tract washings revealed no correlation with lung score. Six weeks after challenge, pigs previously vaccinated intramuscularly mostly demonstrated greater IgG and IgA responses in respiratory tract washings, and greater IgG serum antibody responses, than those vaccinated by intraperitoneal injection.
Conclusion Pigs vaccinated with M hyopneumoniae antigens in the molecular size range of 70 to 85 kDa showed a significant reduction in lung lesions compared with unvaccinated control animals after experimental challenge. IgG and IgA antibody concentrations in serum and respiratory tract washings after vaccination do not provide a useful prognostic indicator of protection from enzootic pneumonia.     

Effect of enzootic pneumonia of pigs on growth performance

Growing pigs were naturally infected with a field strain of Mycoplasma hyopneumoniae to assess the effect of enzootic pneumonia on production. Both the initial ("breakdown") and endemic stages of infection were evaluated. The pigs were reared under environmental and management conditions commonly found on commercial piggeries in South Australia. Growth rate of pigs held in-contact with inoculated pigs was reduced by 12.7% (p less than 0.01) between 50 to 85 kg bodyweight. In the second trial inoculated gilts were used to naturally infect piglets during suckling. Growth rate of infected pigs was reduced by 15.9% (p less than 0.001) between 8 to 85 kg bodyweight, while feed conversion was depressed by 13.8% (p less than 0.05) between 10 to 25 kg bodyweight. At current feed and production costs this reduced performance added approximately $2.80 to the cost of every pig produced. These losses were recorded in groups of pigs in which enzootic pneumonia was present. At slaughter, 40% of lungs contained gross lesions of enzootic pneumonia which were free of significant secondary bacteria. The nature of the infection was established by gross and microscopic pathology and confirmed by the detection of specific complement fixing antibody in infected pigs and the demonstration of M. hyopneumoniae by direct immunofluorescent staining of lung sections.