Mannheimia Haemolytica Pneumonia

Mannheimia haemolytica pneumonia is a severe bacterial respiratory infection that represents one of the most economically significant diseases affecting cattle and small ruminants worldwide. The disease is characterized by acute fibrinous pleuropneumonia with extensive lung consolidation, toxin-mediated tissue damage, and high morbidity and mortality rates in affected populations. Mannheimia haemolytica is the primary bacterial pathogen involved in bovine respiratory disease complex, commonly known as shipping fever due to its frequent occurrence following transportation stress. This condition causes billions of dollars in losses to the cattle industry annually through death, treatment costs, reduced performance, and carcass condemnation.

The disease primarily affects cattle but also occurs in sheep and goats, where it causes similar pneumonic disease patterns. In cattle, Mannheimia haemolytica pneumonia most commonly develops in recently weaned calves, animals following transportation to feedlots, and those experiencing other significant stressors that compromise immune function. The bacterium is a normal commensal of the upper respiratory tract in healthy cattle, becoming pathogenic when host defenses are compromised and allowing rapid bacterial proliferation and invasion of the lower respiratory tract. Sheep are affected by specific serotypes of Mannheimia haemolytica that cause septicemic and pneumonic pasteurellosis, particularly in lambs.

The economic and welfare impact of Mannheimia haemolytica pneumonia is substantial and affects all sectors of the cattle industry. Feedlot operations experience the highest losses due to concentrated populations of susceptible animals and the stress of transportation and commingling. Treatment costs for affected animals are significant, and mortality rates can reach fifteen to thirty percent or higher in severe outbreaks. Surviving animals often show permanently reduced performance, with lower average daily gains and poorer feed efficiency throughout the feeding period. Carcasses may be condemned at slaughter due to lung lesions and adhesions. The animal welfare implications are equally serious, with affected animals experiencing significant pain, respiratory distress, and suffering.

Early detection and appropriate treatment of Mannheimia haemolytica pneumonia significantly improve outcomes, though the rapid progression of disease makes timing critical. Animals treated within the first twenty-four to forty-eight hours of clinical signs have substantially better survival rates and recovery than those treated later in the disease course. Prevention through vaccination, management of risk factors, and metaphylactic treatment of high-risk groups provides the most effective approach to controlling losses from this disease. Understanding the complex interactions between the bacterium, viral co-pathogens, host immunity, and environmental stressors is essential for implementing effective prevention and control programs.

The primary cause of Mannheimia haemolytica pneumonia is overwhelming growth and lung invasion by the bacterium Mannheimia haemolytica, most commonly serotype A1 in cattle. This gram-negative bacterium is a normal resident of the nasopharynx and tonsils in healthy cattle, where it exists in small numbers without causing disease. Under conditions of stress and compromised immunity, the bacteria rapidly multiply in the upper respiratory tract and subsequently colonize the lungs. Once in the lower respiratory tract, Mannheimia haemolytica produces leukotoxin, a potent virulence factor that destroys host immune cells and enables bacterial survival. The bacteria also produce lipopolysaccharide endotoxin that contributes to inflammation and tissue damage.

While Mannheimia haemolytica pneumonia is not hereditary, genetic factors influence host susceptibility to respiratory disease. Studies have identified genetic markers associated with resistance or susceptibility to bovine respiratory disease complex, and heritability estimates for respiratory disease resistance are moderate. Breeds differ in their average susceptibility, with Bos indicus cattle and their crosses generally showing greater resistance than British and Continental beef breeds. Within breeds, significant individual variation exists in immune response capacity and disease resistance. Selection for improved respiratory health is possible but complicated by the multifactorial nature of the disease and challenges in accurately phenotyping resistance.

Environmental and management factors are the primary determinants of Mannheimia haemolytica pneumonia outbreaks in cattle populations. Transportation stress is the classic predisposing factor, with long hauls, temperature extremes, inadequate ventilation, and feed and water deprivation during transit compromising immune function. Commingling of cattle from multiple sources brings together animals with different pathogen exposures and immunity profiles, facilitating disease transmission. Weaning stress, dietary changes, and processing procedures such as castration and dehorning add additional immune challenges. Overcrowded housing, poor ventilation, dust, and ammonia accumulation in confinement facilities further compromise respiratory defenses.

Several risk factors have been identified that increase the likelihood of Mannheimia haemolytica pneumonia in individual animals. Young age is a significant risk factor, with calves between six and twelve months of age being most susceptible. Animals that have not been preconditioned through vaccination and weaning before sale are at elevated risk. Previous respiratory disease episodes increase susceptibility to subsequent infections. Concurrent viral infections, particularly bovine viral diarrhea, infectious bovine rhinotracheitis, parainfluenza-3, and bovine respiratory syncytial virus, predispose to bacterial pneumonia. Nutritional deficiencies, particularly of trace minerals and vitamins important for immune function, increase disease susceptibility.

The pathophysiology of Mannheimia haemolytica pneumonia involves complex interactions between bacterial virulence factors and host immune responses. Initial bacterial colonization of the lungs triggers an intense inflammatory response with recruitment of neutrophils to the site of infection. The bacteria produce leukotoxin that kills these recruited neutrophils, releasing their contents and causing collateral tissue damage. Dead neutrophils and bacteria contribute to the formation of the characteristic fibrinous exudate that fills airways and alveoli. Vascular damage leads to edema, hemorrhage, and thrombosis. The combination of direct bacterial damage, toxin effects, and overly robust but ultimately ineffective immune responses produces the extensive lung consolidation and necrosis characteristic of the disease.

Early warning signs of Mannheimia haemolytica pneumonia may be subtle and require vigilant observation to detect, particularly in large groups of cattle. The earliest indicators often include decreased feed intake and reduced time spent at feed bunks, which may be noticed before obvious respiratory signs develop. Affected animals may lag behind the group when moved and appear less alert or responsive than their pen mates. Subtle depression and mild lethargy may be observed. Early respiratory changes include slightly increased respiratory rate and occasional coughing that can easily be overlooked. Animals may show mild nasal discharge and slight elevation of rectal temperature above normal baseline.

As the disease progresses, symptoms become more pronounced and follow characteristic patterns in cattle. Fever develops rapidly, with rectal temperatures often exceeding 40 to 41 degrees Celsius in acute cases. Respiratory distress becomes obvious, with increased respiratory rate and effort, and animals may breathe with open mouths or have audible breathing. Nasal discharge becomes copious and may progress from clear to mucopurulent. Coughing becomes frequent and may be spontaneous or induced by handling. Affected cattle often stand with heads lowered and necks extended to facilitate breathing. In sheep and goats, similar respiratory signs develop with rapid progression to severe dyspnea.

Behavioral changes accompany the physical symptoms and provide additional indicators for identifying affected animals. Sick cattle separate themselves from the group and may be found standing alone at the edges of pens or in corners. They become reluctant to move and may resist handling. Feed and water intake decrease dramatically, and animals lose interest in activities that previously attracted their attention. Rumination decreases or ceases entirely. Affected animals appear depressed and may show signs of ear droop, droopy eyelids, and dull demeanor. Social interactions with pen mates decrease, and sick animals may be displaced from preferred resting areas.

Physical examination findings in cattle with Mannheimia haemolytica pneumonia are characteristic and support clinical diagnosis. Auscultation of the chest reveals harsh or absent breath sounds over affected lung areas, with the cranioventral regions most commonly involved early in disease. Percussion may demonstrate dullness corresponding to consolidated lung tissue or pleural fluid accumulation. Heart rate is elevated, often exceeding ninety beats per minute. Mucous membranes may appear congested or develop cyanotic discoloration in severe cases. Dehydration develops rapidly due to fever and reduced water intake. Body condition declines as the disease progresses, with visible weight loss apparent within days.

The progression of symptoms in untreated Mannheimia haemolytica pneumonia is typically rapid, with animals deteriorating significantly over twenty-four to seventy-two hours. Initial mild signs quickly advance to severe respiratory distress with open-mouth breathing and extended head and neck. Nasal discharge becomes profuse and may become blood-tinged in advanced cases. Fever may remain elevated or decline terminally as sepsis develops. Animals become increasingly weak and reluctant to stand. In peracute cases, death may occur within twenty-four hours of the first observed signs. Those that survive the acute phase without treatment often develop chronic pneumonia with permanent lung damage.

Emergency symptoms requiring immediate veterinary intervention include severe respiratory distress with open-mouth breathing and extended tongue, cyanosis of the muzzle and mucous membranes, recumbency with inability or unwillingness to rise, temperatures exceeding forty-one point five degrees Celsius, and signs of septic shock including cold extremities and weak rapid pulse. Animals showing these signs have advanced disease with a poor prognosis even with aggressive treatment. Sudden death can occur in peracute cases, sometimes affecting multiple animals in an affected group within a short period. Any animal showing rapid deterioration or failure to respond to initial treatment requires immediate veterinary evaluation.

Clinical examination by a licensed veterinarian familiar with bovine respiratory disease provides the foundation for diagnosis of Mannheimia haemolytica pneumonia. The examination begins with assessment of the group history, including recent management changes, transportation, commingling, and any previous respiratory disease in the population. Individual clinical examination evaluates respiratory rate and effort, presence and character of nasal discharge, rectal temperature, and attitude and appetite. Thorough chest auscultation assesses the extent of lung involvement, with careful attention to cranioventral lung fields where pneumonia typically begins. The veterinarian will also evaluate for concurrent conditions that may predispose to or complicate respiratory disease.

Diagnostic tests support clinical diagnosis and help guide treatment decisions for Mannheimia haemolytica pneumonia. Thoracic ultrasonography has become increasingly valuable for assessing the extent of lung consolidation and detecting pleural effusion, providing real-time information about disease severity. Blood samples may reveal elevated white blood cell counts with neutrophilia, though severe cases may show neutropenia and a degenerative left shift. Acute phase proteins including fibrinogen and haptoglobin are typically elevated. Transtracheal wash or bronchoalveolar lavage provides samples for cytology and bacterial culture with sensitivity testing, allowing identification of the specific pathogens involved and selection of appropriate antimicrobials.

Differential diagnosis for Mannheimia haemolytica pneumonia includes other causes of acute respiratory disease in cattle that may present with similar clinical signs. Viral respiratory infections including infectious bovine rhinotracheitis, bovine viral diarrhea, and bovine respiratory syncytial virus may cause primary disease or predispose to secondary bacterial pneumonia. Other bacterial pneumonias caused by Pasteurella multocida, Histophilus somni, Mycoplasma bovis, or Trueperella pyogenes must be considered. Lungworm infection can cause respiratory signs in grazing cattle. Aspiration pneumonia from improper oral medication administration should be investigated when appropriate. Toxic pneumonia from inhaled irritants or fog fever in adult cattle may produce similar clinical presentations.

Herd-level diagnostics become important when Mannheimia haemolytica pneumonia affects multiple animals or occurs at unexpectedly high rates. Necropsy examination of acute cases provides valuable diagnostic information through gross and histopathologic evaluation of lung lesions and culture of fresh lung tissue. Review of morbidity and mortality patterns within the affected group can identify risk factors and guide prevention efforts. Assessment of viral disease status through serology or antigen testing helps determine the role of viral predisposing factors. Environmental evaluation of housing, ventilation, and management practices identifies modifiable risk factors. Analysis of treatment outcomes provides feedback on diagnostic accuracy and antimicrobial selection.

Emergency and immediate treatment for cattle with severe Mannheimia haemolytica pneumonia focuses on rapid initiation of antimicrobial therapy and supportive care. Animals in acute respiratory distress should receive appropriate antimicrobials immediately upon diagnosis without waiting for culture results, as delays significantly worsen prognosis. Initial treatment selection should be based on known antimicrobial sensitivities from previous cases on the operation or regional patterns. Commonly used first-line antimicrobials include tulathromycin, florfenicol, enrofloxacin where approved, ceftiofur, and tilmicosin. Anti-inflammatory therapy with approved non-steroidal anti-inflammatory drugs helps reduce fever and pulmonary inflammation. Severely affected animals may benefit from additional supportive measures including fluid therapy for dehydration.

Medical management protocols for Mannheimia haemolytica pneumonia should be established in consultation with the herd veterinarian and tailored to the specific operation and disease patterns encountered. First-line antimicrobial selection should consider efficacy against Mannheimia haemolytica, convenience of administration, withdrawal times, and cost. Single-dose long-acting formulations provide advantages for large-scale feedlot use and improved compliance. Response to initial treatment should be evaluated at forty-eight to seventy-two hours, with animals failing to improve requiring re-evaluation and potential change to second-line therapy. All treatments must be documented with accurate recording of dates, products, dosages, and withdrawal times to ensure food safety compliance.

Supportive care is essential alongside antimicrobial treatment and significantly improves outcomes in affected animals. Sick cattle should be removed from group housing to hospital pens where they can rest without competition for feed and water. High-quality, palatable feeds should be offered to encourage intake. Fresh clean water must be easily accessible. Protection from environmental stressors including temperature extremes, wind, and wet conditions supports recovery. Animals should be handled gently and stressed minimally during the recovery period. Monitoring should be frequent, with assessment of temperature, respiratory rate, appetite, and attitude at least once daily.

Metaphylactic treatment of high-risk groups provides an important tool for controlling Mannheimia haemolytica pneumonia in feedlot settings. Mass antimicrobial treatment of all animals in groups considered at high risk of developing respiratory disease, typically administered at arrival processing, significantly reduces morbidity and mortality. Metaphylaxis is most beneficial for high-risk cattle including those that are lightweight, have been commingled from multiple sources, traveled long distances, or have unknown vaccination history. The economic return on metaphylactic treatment is well established for high-risk populations but may be marginal or negative for lower-risk cattle. Antimicrobial stewardship considerations support targeted use based on risk assessment rather than universal application.

Herd treatment protocols should address both individual animal therapy and population-level disease management. Protocols should define criteria for treatment initiation, antimicrobial selection, treatment duration, and criteria for assessing response. Pull programs identifying animals for treatment based on systematic observation should be established and implemented consistently. Second-line treatment options for animals failing initial therapy should be specified. Criteria for determining treatment failure and recommending salvage or euthanasia should be defined to prevent prolonged suffering in animals unlikely to recover. Regular review of treatment outcomes and antimicrobial sensitivity data allows protocol refinement.

Treatment decisions for Mannheimia haemolytica pneumonia must balance animal welfare considerations with economic realities of cattle production. Early detection and prompt treatment provide the best outcomes for individual animals and the most favorable economic returns. However, animals with chronic pneumonia that have failed multiple treatments have poor prognoses and continued treatment provides limited benefit while incurring ongoing costs. Decisions regarding euthanasia or salvage slaughter for non-responsive cases should be made in consultation with the herd veterinarian, considering both humane factors and economic considerations. Appropriate withdrawal times must always be observed for animals sent to slaughter following treatment.

Recovery timeline for cattle treated for Mannheimia haemolytica pneumonia varies considerably based on disease severity at the time of treatment initiation and individual animal response. Animals treated early in the disease course, typically within twenty-four hours of first signs, often show improvement in fever and attitude within forty-eight to seventy-two hours. Respiratory signs may take longer to resolve, with coughing and elevated respiratory rate persisting for one to two weeks even in successful treatment cases. Animals with more advanced disease require longer recovery periods and may show incomplete resolution of respiratory signs. Those developing chronic pneumonia following acute illness may never fully recover normal respiratory function.

Post-treatment care and monitoring are essential for optimal recovery outcomes and early detection of treatment failures or relapses. Treated animals should be observed at least daily for the first week following treatment, with assessment of temperature, respiratory rate and effort, appetite, and overall demeanor. Animals showing clinical improvement should continue to recover steadily; any deterioration or failure to progress warrants veterinary re-evaluation. Recheck temperatures at forty-eight to seventy-two hours post-treatment help assess response. Animals may be returned to group housing once acute signs have resolved, though they should be identifiable and continue to receive monitoring attention. Adequate nutrition and low-stress management support continued recovery.

Prognosis for Mannheimia haemolytica pneumonia depends heavily on timing of treatment and severity of lung involvement at presentation. Animals treated early in acute disease have good prognosis for survival and return to productivity, with mortality rates of five to ten percent with appropriate therapy. Those treated later in the disease course or presenting with severe respiratory compromise have a more guarded prognosis, with mortality rates that may exceed thirty percent. Animals that develop chronic pneumonia have a guarded to poor prognosis for return to normal performance, often showing permanently reduced growth rates and feed efficiency. Previous respiratory disease episodes and treatment failures indicate a poor prognosis for subsequent episodes.

Return to production considerations for cattle recovering from Mannheimia haemolytica pneumonia should account for both residual health effects and ongoing performance impacts. Animals that recover from mild disease with early treatment typically perform reasonably well during the remainder of the feeding period, though some reduction in average daily gain compared to unaffected pen mates is common. Those recovering from severe disease or developing chronic pneumonia show more substantial performance decrements and may not achieve acceptable market endpoints. Economic analysis may favor early marketing of chronic cases at lighter weights rather than continued feeding to traditional finish weights. Carcass quality may be affected by lung adhesions and lesions identified at slaughter.

Vaccination protocols are fundamental to prevention of Mannheimia haemolytica pneumonia and should be implemented as part of comprehensive respiratory disease control programs. Vaccines containing Mannheimia haemolytica antigens, including modified live and killed bacterin products with leukotoxoid components, are widely available. Vaccination timing is critical, with animals ideally vaccinated three to four weeks before anticipated stress events such as weaning or transportation to allow development of protective immunity. Booster vaccinations improve and extend protection. Combination vaccines including viral respiratory pathogens provide broad protection against the bovine respiratory disease complex. Intranasal vaccines can provide rapid local immunity and are useful in situations where immediate protection is needed.

Biosecurity and management practices significantly influence Mannheimia haemolytica pneumonia risk and should be optimized as part of prevention programs. Preconditioning programs that wean calves, vaccinate, and acclimate them to bunk feeding before sale substantially reduce respiratory disease risk. Minimizing transportation stress through attention to vehicle ventilation, stocking density, trip duration, and provision of rest stops protects immune function. Avoiding commingling of cattle from multiple sources when possible reduces pathogen exposure and transmission. Quarantine of new arrivals allows time for clinical signs of incubating disease to appear before introduction to the main population.

Nutritional management supports immune function and contributes to respiratory disease prevention. Rations should be balanced to meet all nutrient requirements with particular attention to trace minerals including copper, zinc, selenium, and manganese that support immune function. Vitamin E and vitamin A status should be adequate. Arrival cattle benefit from receiving high-quality, palatable feeds to encourage early intake and rapid recovery from transportation stress. Feed delivery should ensure all animals have adequate bunk access without excessive competition. Fresh clean water should be freely available at all times.

Environmental and housing management reduces respiratory disease pressure in confined cattle populations. Ventilation systems should provide adequate air exchange to remove airborne pathogens, dust, and ammonia while avoiding cold drafts. Stocking density should allow adequate space per animal, typically exceeding fifteen square meters per head in open lots. Bedding should be maintained in clean, dry condition. Hospital pens should be available for separation and treatment of sick animals away from the main population. Facilities should allow low-stress animal handling to minimize the immune-compromising effects of rough treatment.

Arrival management protocols for newly received cattle provide critical opportunities for prevention of Mannheimia haemolytica pneumonia. Processing procedures should be completed efficiently to minimize handling stress. Metaphylactic antimicrobial treatment should be considered for high-risk groups based on established criteria. Vaccination at arrival provides benefits despite the suboptimal timing, though animals that have been previously vaccinated show better responses. Animals should be allowed to rest and access feed and water immediately following arrival. Close observation during the first three weeks identifies animals developing respiratory disease early when treatment is most effective.

Daily management and monitoring requirements for cattle populations at risk of Mannheimia haemolytica pneumonia include systematic observation for early detection of affected animals. Trained personnel should observe cattle at least twice daily, ideally during morning feeding and afternoon checks. Observation should focus on attitude, appetite, respiratory rate and effort, and any animals separated from the group. Pull programs should establish consistent criteria for identifying animals requiring treatment and be implemented uniformly. Personnel should be trained in early disease recognition and understand the importance of prompt treatment. Communication systems should ensure rapid reporting of sick animals to supervisors and veterinary staff.

Housing and environmental management significantly impact respiratory disease expression and should receive ongoing attention. Ventilation systems require regular maintenance and adjustment based on weather conditions and animal numbers. Stocking density should be monitored and adjustments made as animals grow. Bedding management should maintain dry conditions and minimize dust generation. Pen layout should avoid dead air spaces where pathogens can accumulate. Feeding systems should be managed to encourage consistent intake and provide adequate bunk space. Water systems should deliver clean, fresh water at sufficient flow rates for the population housed.

Herd health programs addressing bovine respiratory disease should be comprehensive and regularly updated based on performance data and disease patterns. Vaccination protocols should be established in consultation with the herd veterinarian and consistently implemented. Treatment protocols should define criteria for therapy initiation, antimicrobial selection, supportive care measures, and assessment of treatment response. Case definitions for recording morbidity and mortality should be standardized. Regular review of health performance data with the veterinarian allows identification of trends and opportunities for improvement. Economic analysis of disease costs and prevention investments guides resource allocation.

Record keeping and data management support effective respiratory disease control through enabling analysis of disease patterns and treatment outcomes. Individual animal health records should document all respiratory disease events, treatments administered, and outcomes. Group-level data should track morbidity rates, mortality, treatment costs, and performance impacts. Records should include sufficient detail to allow analysis of risk factors such as source, arrival weight, arrival timing, and weather conditions. Treatment success rates by antimicrobial protocol provide feedback on drug efficacy. Integration of health and production data allows assessment of long-term impacts of respiratory disease on performance and economic outcomes.

Economic considerations should guide investment in Mannheimia haemolytica pneumonia prevention and treatment programs. The costs of prevention including preconditioning, vaccination, and management improvements should be compared against expected disease costs including mortality, treatment expenses, and performance losses. Cost-benefit analysis of metaphylactic treatment helps define high-risk populations for which this intervention is economically justified. Analysis of chronic case management options including continued treatment versus early marketing guides decisions about individual animals. Investment in infrastructure improvements such as ventilation and hospital facilities should be evaluated based on expected returns through improved health outcomes.

High-risk breeds for Mannheimia haemolytica pneumonia include British beef breeds and their crosses, which show relatively higher susceptibility to bovine respiratory disease complex compared to cattle with Bos indicus genetics. Breeds such as Angus, Hereford, and Shorthorn and their crosses demonstrate increased respiratory disease morbidity and mortality in feedlot settings. Holstein and other dairy breeds show high susceptibility to respiratory disease, creating challenges for dairy beef production systems. Continental breeds including Charolais, Simmental, and Limousin show intermediate susceptibility. In contrast, Brahman cattle and other Bos indicus breeds and their crosses demonstrate significantly greater resistance to respiratory disease, though they may face other health challenges in intensive production systems.

Production type strongly influences Mannheimia haemolytica pneumonia risk independent of breed genetics. Feedlot cattle, particularly those that are lightweight, have been commingled from multiple sources, or have traveled long distances, face the highest disease risk. Auction market cattle assembled from numerous small sources carry elevated risk compared to those marketed directly from ranch of origin. Dairy beef calves entering the beef production chain face multiple risk factors including early separation from dams, variable colostrum management, and exposure to pathogens in dairy calf facilities. Beef calves preconditioned at the ranch of origin with vaccination, weaning, and bunk breaking before sale have substantially lower respiratory disease risk than calves sold at weaning without preparation.

Genetic selection for improved respiratory disease resistance offers long-term opportunities to reduce Mannheimia haemolytica pneumonia susceptibility in cattle populations. Research has identified genetic markers associated with bovine respiratory disease susceptibility, and genomic estimated breeding values for respiratory health are becoming available in some breed improvement programs. Heritability estimates for respiratory disease resistance are moderate, suggesting selection progress is achievable but requires sustained effort. Within-herd selection against individuals with histories of respiratory disease removes potentially susceptible genetics. Crossbreeding programs incorporating genetics from disease-resistant breeds can improve population health while maintaining acceptable production characteristics.

Commonly co-occurring conditions with Mannheimia haemolytica pneumonia reflect the multifactorial nature of bovine respiratory disease complex and the consequences of severe bacterial pneumonia. Viral respiratory infections including infectious bovine rhinotracheitis, bovine viral diarrhea, bovine respiratory syncytial virus, and parainfluenza-3 frequently precede or accompany bacterial pneumonia and contribute to disease severity. Pasteurella multocida infection commonly occurs alongside Mannheimia haemolytica and may be isolated from the same animals. Histophilus somni causes both respiratory disease and systemic infections including thrombotic meningoencephalitis. Mycoplasma bovis infection increasingly complicates bovine respiratory disease and is associated with chronic pneumonia and polyarthritis. Concurrent gastrointestinal disease or infectious bovine keratoconjunctivitis may occur in stressed cattle populations.

Conditions with similar symptoms that must be differentiated from Mannheimia haemolytica pneumonia include other causes of acute respiratory disease in cattle. Interstitial pneumonia syndromes including fog fever present with acute respiratory distress in adult cattle. Aspiration pneumonia from improper oral medication or drenching causes acute bacterial pneumonia. Lungworm infection produces respiratory signs in grazing cattle that may mimic bacterial pneumonia. Anaphylactic reactions to injected products can cause acute respiratory distress. Heat stress may produce rapid breathing and open-mouth respiration resembling respiratory disease. Cardiac abnormalities including traumatic pericarditis may present with respiratory signs.

Complications and sequelae of Mannheimia haemolytica pneumonia significantly impact long-term health and productivity in surviving animals. Chronic pneumonia with persistent lung consolidation develops in animals with incomplete resolution of acute infection. Lung abscesses may form within areas of necrotic lung tissue. Pleural adhesions from fibrinous pleuritis restrict lung expansion and cause chronic discomfort. Pericarditis may develop through extension of infection from the lungs. Septicemia and disseminated infection can lead to multiple organ involvement. Long-term performance impacts including reduced average daily gain and feed efficiency affect economic outcomes even in animals that appear clinically recovered.