Mycoplasma Pneumonia

Mycoplasma pneumonia is a significant and increasingly recognized respiratory disease affecting multiple farm animal species, caused by bacteria of the genus Mycoplasma that lack cell walls and produce chronic, often treatment-resistant infections. In cattle, Mycoplasma bovis has emerged as one of the most important respiratory pathogens, contributing substantially to bovine respiratory disease complex and causing chronic pneumonia that responds poorly to conventional antimicrobial therapy. The disease is characterized by caseonecrotic pneumonia with distinctive chronic lesions, frequent association with other manifestations including arthritis, otitis, and mastitis, and significant economic losses through mortality, reduced performance, and treatment costs.

Mycoplasma pneumonia affects cattle, goats, sheep, pigs, and poultry, with different Mycoplasma species causing disease in each host. In cattle, Mycoplasma bovis is the primary pathogen of concern, though other species including Mycoplasma dispar may contribute to respiratory disease. Goats and sheep are affected by Mycoplasma ovipneumoniae, Mycoplasma mycoides subspecies capri, and other species causing contagious caprine pleuropneumonia and related syndromes. Pigs suffer from Mycoplasma hyopneumoniae causing enzootic pneumonia. Poultry species are affected by Mycoplasma gallisepticum and Mycoplasma synoviae. Each host-pathogen combination has unique characteristics influencing diagnosis, treatment, and control approaches.

The economic and welfare impact of mycoplasma pneumonia in livestock operations is substantial and often underappreciated. In cattle, Mycoplasma bovis infections cause significant mortality in severe cases and prolonged illness in survivors. The chronic nature of the disease results in extended treatment periods, increased labor costs, and reduced animal performance that may persist throughout the feeding period. Carcass condemnation at slaughter due to lung lesions and arthritis adds to economic losses. In dairy operations, mycoplasma mastitis causes devastating losses and may lead to whole-herd control challenges. The welfare implications are significant, with affected animals experiencing chronic pain, respiratory compromise, and reduced quality of life.

Mycoplasma pneumonia presents unique challenges for treatment and control because the organisms lack cell walls, rendering them intrinsically resistant to beta-lactam antibiotics and many other commonly used antimicrobials. Infections tend to become chronic despite treatment, and complete elimination of the organism from affected animals is often not achieved. Prevention through biosecurity, herd status monitoring, and management of risk factors provides the most effective approach to controlling mycoplasma diseases in livestock. Vaccines are available for some mycoplasma diseases in certain species and may provide partial protection when used as part of comprehensive control programs.

The primary cause of mycoplasma pneumonia in cattle is infection with Mycoplasma bovis, a small, cell wall-deficient bacterium that colonizes the respiratory tract and spreads to multiple body systems. The organism is transmitted through direct contact with infected animals, aerosol spread of respiratory secretions, and contaminated fomites. Calves may become infected through consumption of milk or colostrum from infected dams with mycoplasma mastitis. Once introduced to a susceptible population, Mycoplasma bovis spreads efficiently, with shedding animals contaminating housing environments and serving as ongoing sources of infection. The organism can persist in carrier animals for extended periods, maintaining infection within herds even when clinical disease is not apparent.

While mycoplasma pneumonia is not hereditary, host factors influence susceptibility to infection and severity of disease. Young animals are more susceptible to clinical disease than adults with established immune function, making pre-weaned calves and recently weaned or transported cattle particularly vulnerable. Individual variation in immune response capacity affects the outcome of exposure. Some evidence suggests breed differences in susceptibility exist, though these are not as well characterized as for other respiratory pathogens. Animals with compromised immunity due to concurrent infections, nutritional deficiencies, or stress experience more severe disease.

Environmental and management factors strongly influence the occurrence and severity of mycoplasma pneumonia outbreaks. Intensive production systems with high animal density facilitate rapid transmission between susceptible individuals. Commingling of cattle from multiple sources, common in feedlot operations, brings together animals with different infection statuses and creates opportunities for spread to naive populations. Inadequate ventilation in housed cattle concentrates infectious aerosols and increases exposure intensity. Transportation stress and associated immunosuppression increase susceptibility to clinical disease following exposure. Poor colostrum management in dairy operations compromises passive immunity and increases calf susceptibility.

Several risk factors increase the likelihood of mycoplasma pneumonia in individual animals and populations. Age is a primary risk factor, with young calves and recently weaned cattle being most susceptible. Purchase of cattle from unknown or multiple sources introduces infection risk, as carrier animals may appear healthy while shedding organism. History of mycoplasma infection in a herd indicates ongoing exposure risk for susceptible animals. Concurrent infections, particularly with other respiratory pathogens, increase the likelihood and severity of mycoplasma disease. Inadequate biosecurity allows introduction and spread of infection.

The pathophysiology of mycoplasma pneumonia involves unique mechanisms related to the organism's distinctive biology. Lacking cell walls, mycoplasmas have flexible shapes that allow intimate association with host cell membranes. Mycoplasma bovis adheres to respiratory epithelium and produces various factors that damage host cells and evade immune responses. The organism can modulate its surface antigens to escape immune recognition, contributing to chronic infection. Host immune responses, while ultimately ineffective at eliminating infection, contribute to tissue damage through inflammatory reactions. The characteristic caseonecrotic lesions of mycoplasma pneumonia result from combinations of direct organism effects and immunopathology.

Early warning signs of mycoplasma pneumonia in cattle may be subtle and easily attributed to other causes, making early detection challenging. Initial indicators include mild depression, slightly reduced feed intake, and decreased activity level compared to healthy herdmates. Young calves may show poor growth despite adequate nutrition. Mild coughing may be present but is often less prominent than with other causes of bacterial pneumonia. Slight elevation of respiratory rate may be detected on careful observation. In dairy calves, early ear infections or head tilting may precede or accompany respiratory signs, providing additional diagnostic clues.

As mycoplasma pneumonia progresses, symptoms become more apparent and follow patterns that may help distinguish the condition from other respiratory diseases. Fever is typically present but may be lower than with acute bacterial pneumonias, often in the range of 39.5 to 40.5 degrees Celsius. Respiratory distress develops with increased rate and effort, though the presentation may be less dramatic than peracute shipping fever. Nasal discharge is usually present, ranging from serous to mucopurulent. Chronic, persistent coughing develops and may continue for weeks to months. Weight loss becomes apparent as the disease progresses, with affected animals failing to maintain condition despite adequate feed availability.

Behavioral changes associated with mycoplasma pneumonia reflect both respiratory compromise and the systemic nature of infection. Affected cattle show decreased activity and spend more time lying down than healthy pen mates. They may separate from the group and be less responsive to handling. Feed intake remains depressed even after initial treatment, contributing to progressive weight loss. Animals may show reluctance to move due to respiratory difficulty or concurrent joint involvement. Ear infections commonly associated with Mycoplasma bovis infection cause head tilting, ear droop, and signs of ear discomfort. Depression and dull demeanor persist throughout the course of disease.

Physical examination findings in cattle with mycoplasma pneumonia vary depending on the stage and extent of disease. Auscultation of the lungs reveals abnormal sounds including increased bronchial tones, crackles, and areas of consolidated lung where breath sounds are diminished or absent. The characteristic chronic lesions of mycoplasma pneumonia often involve cranioventral lung regions extensively. Heart rate may be elevated. Body condition declines progressively. Joint swelling and lameness may be detected in animals with concurrent mycoplasma arthritis, particularly affecting the hock, stifle, and carpus. Ear examination may reveal otitis media with purulent discharge.

The progression of mycoplasma pneumonia typically follows a chronic course that distinguishes it from acute bacterial pneumonias. Unlike shipping fever which may progress rapidly over hours to days, mycoplasma infections often develop over weeks and persist for extended periods. Initial mild signs may wax and wane, with apparent temporary improvements followed by recurrence. Animals may show partial response to antimicrobial treatment with temporary improvement but fail to achieve complete resolution. Chronic cases develop extensive lung pathology that persists even if active infection is controlled. Some animals eventually reach a stable state with chronic lung damage, while others continue to deteriorate.

Emergency symptoms requiring immediate veterinary attention include severe respiratory distress with open-mouth breathing indicating advanced lung involvement, recumbency with inability to rise suggesting systemic compromise, high fever with marked depression suggesting acute exacerbation or secondary infection, and signs of septic arthritis with severe joint swelling and lameness. Rapid deterioration in animals previously stable with chronic disease may indicate complications. Young calves with combined respiratory and ear involvement showing neurologic signs require urgent evaluation. Any signs of systemic illness such as cold extremities, rapid weak pulse, or collapse indicate potentially life-threatening complications.

Clinical examination by a licensed veterinarian provides important initial assessment for suspected mycoplasma pneumonia but cannot definitively distinguish it from other respiratory pathogens. The examination should consider the history including age, source, management, and previous disease in the group or herd. Physical examination evaluates respiratory signs, fever, body condition, and evidence of extrapulmonary involvement such as joint swelling or ear disease. The chronic, treatment-resistant nature of disease and multisystem involvement may suggest mycoplasma as a contributing factor. Response patterns to previous antimicrobial therapy provide useful diagnostic information, as failure to respond to beta-lactam antibiotics supports consideration of mycoplasma involvement.

Diagnostic tests are essential for confirming mycoplasma involvement in respiratory disease cases. Culture of Mycoplasma species requires specialized techniques and media not available in all diagnostic laboratories, and growth may take several days to weeks. Polymerase chain reaction testing provides rapid and specific detection of Mycoplasma bovis and other species from respiratory samples including nasal swabs, transtracheal wash, and bronchoalveolar lavage fluid. Serologic testing can detect antibody responses to mycoplasma infection but may not distinguish current from past exposure. Bulk tank milk testing in dairy herds provides surveillance for Mycoplasma bovis at the herd level. Postmortem sampling of lung lesions provides the best diagnostic material.

Differential diagnosis for mycoplasma pneumonia includes other causes of chronic or treatment-resistant respiratory disease in cattle. Other bacterial pneumonias caused by Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni typically respond better to conventional antimicrobial therapy. Viral respiratory infections may produce initial respiratory disease that predisposes to secondary bacterial complications. Lungworm infection causes chronic respiratory signs in grazing cattle. Lung abscesses from various causes produce persistent respiratory compromise. Chronic aspiration pneumonia may result in treatment-resistant lung disease. In chronic cases, the presence of multisystem involvement including arthritis and otitis supports consideration of mycoplasma.

Herd-level diagnostics provide valuable information about mycoplasma status and guide control decisions. Surveillance testing of apparently healthy animals can identify infected herds before clinical disease is recognized. Bulk tank milk culture or PCR testing provides efficient herd-level monitoring in dairy operations. Testing of replacement animals before introduction identifies potential sources of infection. Necropsy examination of affected or chronically ill animals provides definitive diagnosis and characterizes the extent of disease. Review of herd health records may reveal patterns of chronic respiratory disease, treatment failures, and multisystem illness consistent with mycoplasma involvement.

Emergency and immediate treatment for severe mycoplasma pneumonia cases focuses on stabilization and initiation of appropriate antimicrobial therapy recognizing the limitations of available treatments. Animals in acute respiratory distress require a calm, well-ventilated environment with minimal handling. Anti-inflammatory therapy with non-steroidal anti-inflammatory drugs helps reduce fever and pulmonary inflammation. Antimicrobial selection should consider the unique susceptibility profile of mycoplasmas, which lack cell walls and are inherently resistant to beta-lactam antibiotics. Appropriate first-line options include macrolides such as tulathromycin, tilmicosin, and gamithromycin, fluoroquinolones where approved, tetracyclines, and florfenicol.

Medical management of mycoplasma pneumonia is challenging because available antimicrobials typically suppress rather than eliminate infection. Treatment may result in clinical improvement but often fails to clear the organism, leading to relapse when therapy ends or development of chronic carrier states. Prolonged or repeated treatment courses are commonly required, increasing costs and potentially contributing to antimicrobial resistance development. Combination therapy targeting mycoplasmas and potential co-infecting organisms may improve outcomes. Treatment of concurrent infections and underlying conditions supports overall recovery. Response to treatment should be monitored closely, with realistic expectations about outcomes communicated to producers.

Supportive care is particularly important for mycoplasma pneumonia cases given the limited efficacy of antimicrobial treatment alone. Affected animals should be separated from healthy herdmates to reduce transmission and allow rest and recovery. High-quality, palatable feeds support nutritional status and immune function. Clean, dry, well-ventilated housing reduces respiratory irritation and secondary infection risk. Stress should be minimized through gentle handling and protection from environmental extremes. Animals with concurrent arthritis may benefit from additional pain management and soft bedding. Nursing care including ensuring adequate hydration supports debilitated animals.

Herd-level treatment considerations become important when mycoplasma infection is identified in multiple animals or when herd status suggests widespread exposure. Mass treatment of at-risk groups may reduce transmission and clinical disease incidence but carries concerns about cost, antimicrobial stewardship, and potential selection for resistance. Treatment decisions should consider herd infection status, value of animals at risk, and likelihood of benefit given the chronic nature of mycoplasma infections. In some situations, focusing resources on prevention and control rather than treatment of established infection may be more appropriate.

Treatment decisions for individual animals with mycoplasma pneumonia require careful consideration of prognosis, costs, and animal welfare. Animals detected early with mild disease have better prospects for clinical improvement, though complete cure is unlikely. Those with chronic, advanced disease have poor prognosis despite treatment and may experience ongoing suffering with limited benefit from continued therapy. Joint involvement and extensive lung pathology indicate a particularly guarded outlook. Decisions about continuation versus cessation of treatment should be made in consultation with the attending veterinarian, considering both economic factors and animal welfare. Euthanasia may be appropriate for animals with severe, unresponsive disease.

Producers must observe all relevant withdrawal times when treating food-producing animals for mycoplasma pneumonia. Withdrawal periods vary by drug, formulation, species, and jurisdiction. Extended or repeated treatment courses may require recalculation of withdrawal times from the last treatment dose. Milk from treated dairy cattle must be withheld for appropriate periods. Animals may not be slaughtered for human consumption until withdrawal times have elapsed, which may complicate marketing decisions for beef operations. Accurate treatment records documenting dates, products, dosages, and calculated withdrawal periods are essential for food safety compliance.

Recovery timeline for animals treated for mycoplasma pneumonia is typically prolonged and often incomplete compared to other respiratory diseases. Mild cases may show clinical improvement within one to two weeks of initiating appropriate antimicrobial therapy, though coughing and some respiratory compromise often persist. Moderate to severe cases require extended recovery periods of weeks to months, and many animals never return to normal respiratory function. The chronic nature of mycoplasma infection means that animals may appear stable for periods but experience recurrent clinical episodes. Full recovery with complete clearing of infection is uncommon, and many surviving animals become chronic carriers.

Post-treatment care and monitoring are essential for mycoplasma pneumonia cases and should extend well beyond the initial treatment period. Animals should be observed for signs of relapse including return of fever, worsening respiratory signs, and declining condition. Body weight and condition scoring help assess recovery progress. Development of new clinical manifestations such as joint swelling or ear involvement should prompt veterinary reassessment. Long-term monitoring of growth performance in beef cattle and production parameters in dairy cattle reveals persistent impacts of infection. Animals that fail to thrive despite apparent clinical stability may have extensive chronic lung damage.

Prognosis for mycoplasma pneumonia varies considerably based on timing of diagnosis, severity of disease, and presence of complications. Animals detected early with mild respiratory signs and no systemic involvement have a fair prognosis for clinical improvement, though complete cure is unlikely. Cases with extensive pneumonia carry a guarded prognosis, with many animals developing chronic respiratory compromise. Involvement of joints and other systems worsens the outlook. Young calves with severe disease face particularly poor prospects. Previous treatment failures suggest resistant infection or extensive tissue damage and indicate an unfavorable prognosis for subsequent treatment attempts.

Return to production considerations for animals recovering from mycoplasma pneumonia must account for residual health effects and carrier status. Animals that recover clinically may continue to shed organism and serve as sources of infection for susceptible herdmates. Decisions about retaining recovered animals should consider herd infection status and biosecurity goals. In beef cattle, chronic respiratory compromise reduces growth performance and feed efficiency, potentially affecting economic outcomes of continued feeding. Dairy cattle recovered from mycoplasma respiratory disease may develop mastitis or other complications affecting milk production and quality. Breeding animals should be evaluated carefully before retention, as systemic effects may impact reproductive performance.

Vaccination for mycoplasma diseases in cattle has limitations compared to vaccines for other respiratory pathogens but may provide partial protection as part of comprehensive control programs. Autogenous vaccines prepared from farm-specific Mycoplasma bovis isolates have been used with variable results. Commercial mycoplasma vaccines are available in some regions. Vaccination alone cannot be relied upon to prevent disease and should be combined with biosecurity and management measures. In poultry and swine, vaccines for their respective mycoplasma species play more prominent roles in disease control. Vaccination timing and protocols should be established in consultation with veterinary professionals based on specific operation circumstances.

Biosecurity measures are fundamental to preventing introduction and controlling spread of mycoplasma infections in livestock populations. Maintaining closed herds or sourcing replacements only from known negative herds provides the most effective protection for uninfected populations. Testing new arrivals before introduction to the main herd allows identification of infected animals. Quarantine periods provide opportunity for observation and testing before commingling. In dairy operations, testing bulk tank milk monitors herd status, and individual cow screening identifies infected animals for segregation or culling. Preventing mechanical transmission through equipment and personnel hygiene reduces spread within operations.

Nutritional management supports immune function and may reduce disease severity when exposure occurs. Balanced rations meeting all nutrient requirements maintain immunocompetence in the face of pathogen challenge. Adequate colostrum intake by newborn calves provides passive immunity that protects during the vulnerable early life period. Avoiding feeding waste milk from mastitic cows prevents oral transmission to calves in dairy operations. Trace mineral and vitamin supplementation ensures adequate micronutrient status for immune function. Good nutrition alone cannot prevent infection but may improve outcomes when exposure occurs.

Management practices significantly influence mycoplasma transmission and disease expression. Reducing stocking density decreases direct contact transmission and improves air quality. Providing adequate ventilation reduces aerosol concentration and infectious dose. All-in-all-out management with thorough cleaning between groups reduces environmental contamination. Separating age groups prevents transmission from older animals to susceptible young stock. In dairy operations, proper milking hygiene and parlor management reduce cow-to-cow transmission of mycoplasma mastitis. Prompt identification and segregation of clinically affected animals reduces shedding and exposure of susceptible herdmates.

Monitoring and surveillance programs support early detection of mycoplasma introduction and guide control decisions. Regular testing of apparently healthy animals through bulk tank monitoring or individual sampling identifies infection before clinical disease becomes widespread. Recording and analyzing herd health data may reveal patterns suggesting mycoplasma involvement, such as clusters of chronic pneumonia, treatment failures, or multisystem disease. Necropsy surveillance of animals dying or culled for chronic illness identifies mycoplasma as a contributing factor. Diagnostic testing of treatment-resistant respiratory cases detects new infections in previously negative herds.

Daily management and monitoring for operations dealing with mycoplasma pneumonia requires heightened attention to individual animal health and early intervention. Personnel should be trained to recognize the subtle early signs of mycoplasma disease including mild depression, reduced appetite, and poor growth. Daily observations should focus on respiratory signs, attitude, and any evidence of ear or joint involvement that may accompany respiratory disease. Pull programs for treatment should have low thresholds for animals from groups with known mycoplasma exposure. Monitoring should continue for extended periods following treatment, as relapse is common with mycoplasma infections.

Housing and environmental management are particularly important for operations dealing with mycoplasma because the organism spreads efficiently in confined environments with high animal density. Ventilation systems should provide excellent air exchange to reduce airborne pathogen concentration while protecting animals from drafts. Stocking density should be reduced below typical levels when mycoplasma is present to decrease direct contact transmission. Bedding should be kept clean and dry to minimize environmental pathogen load. Hospital facilities should provide isolation for affected animals to reduce transmission to healthy herdmates. All-in-all-out management with thorough cleaning and disinfection between groups helps reduce environmental contamination.

Herd health programs addressing mycoplasma should be developed with veterinary guidance and tailored to the specific circumstances of each operation. Programs should define the operation's approach to mycoplasma including whether the goal is elimination, control, or management of endemic infection. Testing protocols should be established for herd monitoring and evaluation of purchased animals. Treatment guidelines should address initial therapy, assessment of response, and criteria for treatment discontinuation. Decision protocols for chronically affected animals including criteria for continued treatment, culling, or euthanasia should be specified. Regular program review with assessment of outcomes allows continuous improvement.

Record keeping for operations with mycoplasma problems should capture information needed to manage affected individuals and track herd status. Individual animal records should document disease episodes, treatments administered, responses, and long-term outcomes. Group and herd-level data should track incidence of clinical disease, treatment costs, mortality, and performance impacts. Source information for purchased animals supports tracing of infection introduction. Test results from surveillance programs should be maintained for trend analysis. Integration of health and production data allows assessment of mycoplasma impacts on operational performance.

Economic considerations are particularly important for mycoplasma pneumonia because of the chronic nature of disease and limited treatment efficacy. The costs of an infected herd include not only direct treatment expenses and mortality but also reduced performance in clinically affected animals and subclinical impacts across the population. Investment in prevention through biosecurity and management improvements should be weighed against these ongoing losses. For individual animals, cost-benefit analysis should consider low likelihood of complete cure when making treatment decisions. Operations severely affected by mycoplasma may need to consider depopulation and repopulation with negative stock as the most economically sound approach.

High-risk breeds and species for mycoplasma pneumonia are primarily those managed in intensive production systems where transmission is facilitated by close contact and high animal density. In cattle, dairy breeds face high exposure risk in calf-rearing facilities where multiple sources of infection converge. Beef breeds entering feedlots from auction markets and backgrounding operations experience elevated risk due to stress and commingling. Holstein dairy calves entering beef production channels face multiple risk factors including young age at marketing, variable colostrum management, and exposure during transport and commingling. British beef breeds may show higher susceptibility to respiratory disease overall, though specific breed differences for mycoplasma are not well characterized.

Production type strongly influences mycoplasma pneumonia risk in cattle. Dairy operations face particular challenges because Mycoplasma bovis causes mastitis as well as respiratory disease, creating multiple introduction routes and within-herd transmission pathways. Calves fed waste milk from mycoplasma-positive cows become infected through the oral route. Intensive calf-rearing facilities with calves from multiple sources have high transmission potential. Beef feedlots receiving cattle from diverse sources face introduction risk with each new arrival. Cow-calf operations may maintain endemic infection that spreads to calves. Small ruminant operations with intensive management face similar challenges with their species-specific mycoplasma pathogens.

Genetic selection specifically for mycoplasma resistance is not currently available, though general selection for respiratory health and immune function may provide some benefit. Individual variation in susceptibility to mycoplasma infection and severity of disease likely has genetic components that could potentially be selected for with appropriate research and tools. Currently, management factors and exposure history are far more important determinants of disease risk than genetics. Selection against respiratory disease broadly, where genetic tools are available, may indirectly reduce mycoplasma susceptibility. Avoiding purchase of animals with history of chronic respiratory disease or from known positive herds reduces genetic introduction of susceptible individuals.

Commonly co-occurring conditions with mycoplasma pneumonia reflect both the multisystem nature of mycoplasma infections and the frequent involvement of multiple pathogens in bovine respiratory disease. Mycoplasma arthritis commonly accompanies respiratory disease, particularly in calves, causing lameness and joint swelling that may be the presenting complaint. Otitis media is frequently associated with Mycoplasma bovis infection in calves and may occur before, during, or after respiratory disease episodes. Other respiratory pathogens including Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni frequently co-infect with mycoplasma, complicating both diagnosis and treatment. Viral respiratory infections often precede or accompany bacterial pneumonia. In dairy cattle, mycoplasma mastitis may occur in animals with systemic infection.

Conditions with similar symptoms requiring differentiation from mycoplasma pneumonia include other causes of chronic respiratory disease in cattle. Chronic pneumonia from other bacterial pathogens may be difficult to distinguish clinically from mycoplasma infection. Lung abscesses cause persistent respiratory compromise and treatment resistance that mimics mycoplasma disease. Lungworm infection in grazing cattle produces chronic respiratory signs. Tuberculosis, where it occurs, causes chronic respiratory disease with similar presentation. Neoplastic conditions affecting the respiratory system may produce chronic signs. The presence of concurrent ear disease, arthritis, or poor response to conventional antibiotics supports consideration of mycoplasma involvement.

Complications and sequelae of mycoplasma pneumonia significantly impact long-term outcomes for affected animals. Chronic lung damage with caseonecrotic lesions persists even after clinical recovery and permanently reduces respiratory capacity. Extension of infection to joints results in mycoplasma arthritis with chronic lameness and reduced mobility. Otitis media complications may include neurologic involvement with head tilt and incoordination. Chronic carrier states maintain infection within herds and provide ongoing exposure risk for susceptible animals. Reduced growth performance and feed efficiency persist in animals that survive severe infection. Secondary bacterial infections may complicate chronic mycoplasma pneumonia.