Antimicrobial Stewardship in Equine Respiratory Disease: Evidence-Based Use

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-08-11

Key Takeaways

• Distinguishing bacterial from viral, fungal, or non-infectious inflammatory respiratory conditions is paramount before initiating antimicrobial therapy in horses; adult horses with acute fever and nasal discharge are typically viral and require supportive care for 48-72 hours, while foals with pneumonia necessitate prompt antibiotic intervention due to rapid progression.
• Purulent nasal discharge alone is not diagnostic of bacterial infection, as it can occur in viral and inflammatory diseases; fever persisting beyond 72 hours with respiratory signs, abnormal lung sounds (cranioventral crackles), tachypnea, or neutrophilia with left shift are stronger indicators of bacterial involvement, warranting diagnostic sampling.
• Diagnostic sampling via tracheal wash or bronchoalveolar lavage for cytology and quantitative culture with susceptibility testing is crucial, especially for multidrug-resistant organisms or treatment failures, and is cost-effective compared to empirical therapy and resistance selection.
• Antimicrobial stewardship in equine respiratory disease is critical due to limited evidence bases and substantial, poorly characterized prescribing; decisions rely on professional judgment, pharmacokinetic data, and susceptibility testing, not comprehensive clinical trials.
• Specific conditions where antimicrobials are generally not indicated include uncomplicated viral respiratory infections, mild to moderate equine asthma without confirmed bacterial infection, and mild upper respiratory signs without systemic illness, emphasizing supportive care and environmental management.
• Bacterial pneumonia, pleuropneumonia, guttural pouch empyema, and neonatal sepsis with respiratory involvement are conditions where antimicrobials are indicated, with selection guided by culture and susceptibility testing, and route of administration dictated by disease severity (parenteral for systemic signs).

Antimicrobial stewardship in equine respiratory medicine requires the clinician to distinguish bacterial infection from viral infection, fungal disease, and non-infectious inflammatory conditions before committing to therapy. The equine respiratory tract is continuously exposed to environmental organizms, yet most acute respiratory episodes in adult horses are viral or self-limiting. This article provides a decision framework for the practicing veterinarian, organized around the clinical questions that arise at the point of care: when is an antibiotic indicated, when can it be safely withheld, and how should therapy be monitored and adjusted when it is prescribed.

The evidence base for equine respiratory antimicrobial use is narrower than for small animal or food animal medicine. Surveillance data from the United States show that antibiotic prescribing in equine practice is substantial but poorly characterized at national level, with no federal or state programs tracking use in horses despite the recognized importance of this sector to antimicrobial resistance antimicrobial prescribing surveys in Minnesota and North Dakota equine practice. The clinician therefore works within a framework of professional judgment, published pharmacokinetic data, and susceptibility testing, instead of comprehensive clinical trial evidence. This article reviews the pathophysiological basis for antimicrobial decisions in equine respiratory disease, the major clinical syndromes, and the monitoring parameters that support responsible use. Specific drug protocols and doses are not provided, current formulary and label references must be consulted for any therapeutic decision.

At a Glance

The Pathophysiological Basis for Antimicrobial Decisions

The equine lower respiratory tract maintains sterility through mucociliary clearance, alveolar macrophages, and local immunoglobulin production. Bacterial pneumonia develops when these defenses are overwhelmed, most commonly after viral damage to the respiratory epithelium, aspiration, or hematogenous spread. The primary pathogens in adult horses are Streptococcus equi subsp. zooepidemicus, Actinobacillus equuli, and Pasteurella species. In foals, Rhodococcus equi, S. zooepidemicus, and enteric Gram-negative organizms predominate. The distinction between primary bacterial pneumonia and secondary bacterial invasion after viral infection is clinically important because it determines whether antimicrobial therapy is necessary at all.

Viral respiratory infections in horses are caused predominantly by equine influenza virus and the equine alphaherpesviruses, with equine viral arteritis, African horse sickness virus, and Hendra virus establishing systemic infections that may manifest with respiratory signs viral causes of equine respiratory disease. Treatment of these viral infections is supportive, targeted antimicrobial therapy is effective only in bacterial disease. The clinician who prescribes antibiotics for every febrile respiratory horse treats the viral majority unnecessarily while delaying identification of the bacterial minority that genuinely needs therapy.

Antimicrobial Pharmacology Relevant to the Respiratory Tract

The pharmacokinetic properties of an antimicrobial determine its suitability for respiratory infection. Trimethoprim/sulfonamide combinations have been used extensively in equine respiratory disease because of their activity against common respiratory pathogens and their relatively good oral absorption trimethoprim/sulfonamide combinations in the horse. However, peak serum concentrations vary significantly between individual horses, and feed intake affects serum concentrations after oral administration. This variability matters clinically: a drug that achieves therapeutic concentrations in one horse may fall below the minimum inhibitory concentration in another, with the same dose and route.

Penicillins and cephalosporins achieve good concentrations in bronchial secretions and pulmonary tissue. Aminoglycosides penetrate respiratory secretions poorly but are bactericidal and are often combined with beta-lactams for severe pneumonia. Macrolides are the mainstay for Rhodococcus equi in foals because of their intracellular penetration and activity against the organizm within macrophages. Fluoroquinolones have excellent tissue penetration but are reserved for cases with confirmed susceptibility or treatment failure, given their importance in human medicine and the potential for resistance selection.

The Problem of Antimicrobial Resistance in Equine Respiratory Pathogens

Respiratory pathogens of horses are acquiring resistance through multiple mechanisms. Acinetobacter baumannii has emerged as a veterinary nosocomial pathogen capable of causing lower respiratory tract infection in horses, with an extraordinary ability to accumulate resistance determinants and survive in the hospital environment Acinetobacter in veterinary medicine. Infections with this organizm are often multidrug resistant, and treatment should be based on in vitro susceptibility testing instead of empirical choice. The organizm's capacity for environmental persistence means that infection control measures, also antimicrobial selection, are central to management.

The broader resistance problem extends beyond recognized nosocomial pathogens. Gram-negative respiratory isolates in horses increasingly show resistance to first-line agents, and the lack of new antimicrobials in development places pressure on existing drugs outer membrane protein vaccine targets for Burkholderia and related Gram-negative pathogens. This context reinforces the stewardship principle that every antimicrobial prescription carries a population-level cost, also an individual patient benefit.

Diagnostic Reasoning Before the First Dose

The decision to prescribe an antibiotic for equine respiratory disease should follow a structured assessment. Signalment, vaccination status, and epidemiological history identify risk groups. A foal with pneumonia requires immediate therapy because bacterial infection is common and progression to severe disease is rapid. An adult horse with acute onset fever, cough, and serous nasal discharge during an influenza outbreak is more likely to have viral infection, and antibiotics are not indicated unless fever persists beyond 72 hours or the character of the discharge becomes frankly purulent with systemic signs.

Diagnostic sampling before the first dose is ideal but not always feasible in practice. Tracheal wash provides cytology and culture material that distinguishes suppurative inflammation with bacterial growth from eosinophilic or neutrophilic inflammation without organizms. Bronchoalveolar lavage is preferred for suspected asthma. When sampling is performed, the clinician should request quantitative culture and susceptibility testing, particularly for organizms known to be resistant. The cost of sampling is small compared with the cost of a failed course of therapy and the selection pressure exerted by an unnecessary antibiotic.

Clinical Decision Framework for Common Respiratory Presentations

The decision to prescribe an antimicrobial in equine respiratory disease rests on a small number of clinical questions. Does the horse have bacterial infection, or is the process viral, allergic, or mechanical? If bacterial infection is present, is it primary or secondary? Will antimicrobial therapy change the outcome, or will supportive care suffice? These questions are best answered through a structured assessment that combines clinical examination, localizing diagnostics, and, where indicated, cytology and culture.

Acute Onset Fever and Cough in the Adult Horse

Acute respiratory signs in a vaccinated adult horse are most often viral. Equine influenza and equine herpesvirus infections account for a substantial proportion of these presentations, and neither responds to antimicrobial therapy equine viral respiratory disease review. The clinical challenge is distinguishing uncomplicated viral infection from secondary bacterial pneumonia, which develops in a minority of cases.

The following findings shift the probability toward bacterial infection and justify antimicrobial initiation:

• Fever persisting beyond 72 to 96 hours despite nonsteroidal anti-inflammatory support
• Abnormal lung sounds on thoracic auscultation, particularly cranioventral crackles or wheezes
• Tachypnoea or increased respiratory effort at rest
• Malodorous breath or purulent nasal discharge
• Neutrophilia with left shift or toxic change on hematology
• Elevated serum amyloid A or fibrinogen

A horse with clear nasal discharge, normal lung sounds, and fever that resolves within 48 to 72 hours does not require antimicrobials. The owner should be counselled that antimicrobial use in this setting selects for resistant commensal flora without shortening the viral illness. This position aligns with the broader stewardship principle that antimicrobials are indicated only when bacterial infection is confirmed or strongly suspected AVMA antimicrobial use and resistance guidance.

The Febrile Foal

Foals present a different calculus. Sepsis is the leading cause of morbidity and mortality in neonates, and respiratory signs may be the first indication of systemic bacterial infection. The consequences of delayed therapy in a septic foal are severe, and the threshold for antimicrobial initiation is therefore lower than in adults.

In a foal under 14 days of age with fever, lethargy, or respiratory distress, antimicrobial therapy should begin immediately after blood culture and tracheal wash are collected. The initial choice should cover gram-positive and gram-negative organizms, including enteric pathogens. The decision to continue therapy beyond 48 to 72 hours is guided by culture results, clinical response, and serial acute phase protein measurement. A foal that stabilizes and cultures no significant organizm may be a candidate for early discontinuation, but this decision requires careful daily reassessment.

Chronic or Recurrent Respiratory Signs

Recurrent cough, nasal discharge, or exercise intolerance in a mature horse is more often due to noninfectious airway disease than to bacterial infection. Equine asthma, in its mild to severe forms, produces airway inflammation without bacterial proliferation. Antimicrobials do not treat the underlying inflammatory process and should not be prescribed for asthma unless there is documented bacterial infection on tracheal wash cytology and culture.

The diagnostic sequence for the chronic case is:

1. Thoracic auscultation and rebreathing examination
2. Hematology and acute phase proteins
3. Tracheal wash or bronchoalveolar lavage for cytology and culture
4. Thoracic ultrasonography if pleural effusion or consolidation is suspected
5. Endoscopy of the upper airway to exclude guttural pouch disease or other mechanical causes

Cytology showing neutrophilic inflammation with intracellular bacteria supports bacterial infection. Cytology showing predominantly eosinophils or mast cells points toward asthma and away from antimicrobial use. A positive culture without corresponding cytologic inflammation may represent contamination or colonisation and does not by itself mandate therapy.

Conditions Where Antimicrobials Are Usually Not Indicated

Several common presentations tempt antimicrobial use but do not benefit from it. Recognizing these situations is a core stewardship skill.

Uncomplicated Viral Respiratory Infection

As discussed above, viral upper respiratory infection in the adult horse is self-limiting. Antimicrobials do not prevent secondary bacterial infection and may increase the risk of selecting resistant organizms. Supportive care, rest, and monitoring for the development of bacterial complications are the appropriate management.

Equine Asthma

Mild to moderate equine asthma is an inflammatory airway disease. Antimicrobials have no role in its management unless a bacterial component is confirmed. The primary interventions are environmental modification, bronchodilators, and corticosteroids. Prescribing antimicrobials for a horse with asthma and no cytologic evidence of bacterial infection is both ineffective and contrary to stewardship principles.

Mild Upper Respiratory Signs Without Systemic Illness

A horse with serous nasal discharge, normal appetite, and normal temperature likely has a viral or allergic process. Antimicrobials are not indicated. The owner should monitor temperature, appetite, and respiratory effort and seek re-evaluation if signs worsen or persist beyond 7 to 10 days.

Conditions Where Antimicrobials Are Indicated

Bacterial Pneumonia

Confirmed or strongly suspected bacterial pneumonia warrants antimicrobial therapy. The choice of agent should be guided by tracheal wash culture and susceptibility testing whenever possible. Empiric therapy, when required, should target the most likely equine respiratory pathogens, including Streptococcus equi subsp. zooepidemicus, Pasteurella spp., and Actinobacillus spp.

Pleuropneumonia

Pleuropneumonia requires aggressive antimicrobial therapy, often with a combination of agents to achieve adequate pleural penetration and cover mixed infections. Drainage of the pleural space is equally important and may be more critical to outcome than the antimicrobial choice. Therapy is prolonged, typically 2 to 4 weeks or longer, and should be guided by serial clinical assessment, thoracic ultrasonography, and culture results.

Guttural Pouch Empyema

Bacterial infection of the guttural pouch requires antimicrobial therapy combined with lavage and drainage. The choice of antimicrobial should reflect culture results from the pouch contents. Streptococcus equi subsp. equi (strangles) is a common isolate, and the approach to strangles differs from that of other bacterial infections in that antimicrobial therapy may be withheld in uncomplicated cases to allow immunity to develop.

Neonatal Sepsis with Respiratory Involvement

As noted, febrile or systemically unwell foals require prompt antimicrobial therapy. The respiratory tract is a common portal of entry, and the antimicrobial choice must cover the range of neonatal pathogens.

Antimicrobial Selection and Route of Administration

The route of administration should match the severity of disease. A horse with pneumonia and systemic signs requires parenteral therapy, at least initially. Oral therapy may be appropriate for milder infections or for continuation of therapy after initial stabilization.

Trimethoprim-sulfonamide combinations are widely used in equine respiratory disease and have activity against many common respiratory pathogens. However, oral absorption is variable between individual horses, and feed intake affects serum concentrations trimethoprim/sulfonamide combinations in the horse. A horse that is not eating reliably may not achieve therapeutic serum concentrations from oral trimethoprim-sulfonamide therapy, and parenteral therapy should be used in that setting.

The following table summarizes the recommended antimicrobial approach for common equine respiratory conditions.

Monitoring and Reassessment

The decision to start antimicrobials carries an obligation to monitor response and stop therapy when it is no longer needed. A horse on antimicrobial therapy for bacterial pneumonia should be reassessed at 48 to 72 hours. Improvement is expected in temperature curve, appetite, attitude, and respiratory effort. Lack of improvement within this window should prompt re-evaluation of the diagnosis, review of culture and susceptibility results, and consideration of complications such as pulmonary abscessation or pleuropneumonia.

Serial measurement of serum amyloid A or fibrinogen can document resolution of inflammation and support the decision to discontinue therapy. Clinical improvement, instead of a fixed duration of treatment, should guide the length of the antimicrobial course. A horse that is afebrile, eating normally, and has improving lung sounds may be a candidate for early discontinuation, whereas a horse with persistent fever or neutrophilia requires continued therapy and further investigation.

Documentation should record the indication for antimicrobial use, the diagnostic evidence supporting bacterial infection, the agent chosen, the dose and route, the planned reassessment date, and the criteria for discontinuation. This record supports continuity of care and provides a basis for reviewing prescribing patterns within the practice. Practices that track their own antimicrobial use can identify opportunities to reduce unnecessary prescribing, a step that aligns with the broader goal of preserving antimicrobial effectiveness antibiotic prescribing survey in equine and small animal practice.

Special Considerations

The approach described here assumes a hospital or ambulatory setting with access to diagnostic laboratory services. In field practice without immediate access to cytology or culture, the clinician must rely on clinical judgment and a higher threshold for antimicrobial initiation in adults. The cost of a tracheal wash is often less than the cost of an unnecessary antimicrobial course, and the diagnostic value is substantial.

Regional differences in antimicrobial resistance patterns affect empiric choices. A practice that serves a region with high rates of multidrug-resistant Acinetobacter or other nosocomial pathogens should have a lower threshold for culture and susceptibility testing and a higher index of suspicion for resistant infection in hospitalized horses Acinetobacter in veterinary medicine. Similarly, the presence of a hospitalized horse with a resistant infection should prompt review of infection control practices and antimicrobial use across the caseload.

Regulatory requirements for antimicrobial use vary by jurisdiction. The clinician must be familiar with local rules governing prescription, extralabel use, and record keeping FDA animal drug information. These requirements do not change the clinical decision framework, but they do affect how antimicrobials are procured, prescribed, and documented.

Recognized Complications and Early Detection

The most consequential failure in equine respiratory antimicrobial therapy is persistence of infection despite apparent clinical improvement. Fever lysis and improved appetite can precede radiographic or ultrasonographic resolution of pulmonary consolidation by days. A horse that becomes afebrile but retains tachypnoea, nasal discharge, or abnormal lung sounds warrants repeat thoracic imaging instead of cessation of therapy. Serial rectal temperature, respiratory rate at rest, and thoracic auscultation performed every 12 to 24 hours provide the earliest objective signals of treatment failure.

Pleuropneumonia introduces additional failure modes. A fibrinopurulent pleural effusion can loculate, creating pockets that systemic antimicrobials penetrate poorly. Daily thoracic ultrasonography in hospitalized cases detects new loculations before they become clinically apparent. Failure of pleural fluid character to improve, or reaccumulation of fluid after drainage, indicates inadequate source control instead of antimicrobial failure per se. Antimicrobial selection cannot compensate for incomplete drainage.

Antimicrobial-associated diarrhea is the most common adverse event requiring intervention. The macrocyclic lactones and, less frequently, potentiated sulphonamides have been associated with disruption of the hindgut microbiota. Early detection relies on monitoring fecal consistency and hydration status in hospitalized horses. A single soft fecal ball warrants continued observation, profuse watery diarrhea with progressive dehydration mandates discontinuation of the suspect drug and supportive care. The clinician should distinguish this from undifferentiated diarrhea unrelated to antimicrobial therapy, which occurs in hospitalized populations regardless of drug exposure.

Clostridioides difficile colitis represents the severe end of this spectrum. Detection depends on clinical suspicion combined with assay for toxin A and B or PCR on fecal samples. Treatment requires drug withdrawal, fluid therapy, and specific antitoxin measures where indicated. The incidence is low but the consequences are sufficiently grave that any horse developing acute diarrhea while receiving antimicrobials should be managed as potentially clostridial until proven otherwise.

Common Errors and Corrective Actions

Less experienced clinicians frequently initiate antimicrobials for undifferentiated fever before performing a complete physical examination. A horse with a temperature of 38.9°C and no respiratory signs may have a musculoskeletal injury, colitis, or a non-infectious inflammatory condition. The corrective action is to complete the examination, including thoracic auscultation, digital pulse evaluation, and abdominal palpation per rectum where indicated, before prescribing.

A second recurring error is treating the radiograph instead of the horse. A mild interstitial pattern on thoracic radiography in a horse with normal vital parameters and no nasal discharge does not constitute bacterial pneumonia. Conversely, a normal radiograph does not exclude early pneumonia in the adult horse, where cranioventral consolidation may be obscured by the shoulder musculature. Ultrasonography of the cranial lung fields is more sensitive for peripheral consolidation and should be performed when clinical suspicion is high despite unremarkable radiographs.

The third common error is extending antimicrobial therapy beyond the point of clinical resolution. Many horses receive 10 to 14 days of treatment when 5 to 7 days would suffice for uncomplicated pneumonia. The corrective action is to define the treatment endpoint at initiation: normal temperature for 48 hours, normal appetite, and improving respiratory effort. Therapy should stop when these criteria are met, not when the calendar reaches an arbitrary day count.

Limitations of the Evidence and Divergent Expert Opinion

The equine respiratory antimicrobial literature is dominated by pharmacokinetic studies and retrospective case series. Prospective randomised controlled trials comparing antimicrobial regimens for pneumonia or pleuropneumonia are scarce, and none has sufficient power to detect differences in mortality or complication rates. Consequently, many prescribing decisions rest on expert opinion and extrapolation from other species. The review of trimethoprim/sulphonamide combinations in the horse illustrates this pattern: the drug class has been used for decades, yet the evidence base consists largely of pharmacokinetic data and clinical experience instead of controlled efficacy trials.

Expert opinion diverges on several specific questions. Whether potentiated sulphonamides remain first-line for community-acquired pneumonia in the adult horse is contested, with some authorities favouring them for cost and oral bioavailability and others preferring penicillin combined with an aminoglycoside for broader gram-negative coverage. The role of rifampicin in pulmonary abscessation is similarly debated. Most experts agree it penetrates abscesses well, but concerns about resistance selection and drug interactions lead some to reserve it for confirmed Rhodococcus equi infection in foals.

The significance of in vitro resistance for clinical outcome is poorly defined. A pathogen reported as resistant to a drug may still respond in vivo when the drug concentrates in pulmonary tissue or when host defenses contribute to clearance. Conversely, in vitro susceptibility does not guarantee clinical efficacy in the face of poor perfusion, loculated infection, or biofilm formation. Culture and susceptibility testing should guide therapy, but the results must be interpreted within the clinical context. The veterinary nosocomial pathogen literature emphasizes that multidrug-resistant organizms such as Acinetobacter baumannii require susceptibility-guided therapy and rigorous infection control, yet even here clinical outcome data in horses are limited to case reports and small series.

Referral, Consultation, and Reporting

Referral is indicated when the horse fails to respond to appropriate first-line therapy within 72 hours, when pleuropneumonia requires indwelling thoracic drainage, when the clinician lacks access to thoracic ultrasonography or computed tomography, or when the patient's condition deteriorates despite supportive care. Specialist consultation with a large animal internal medicine diplomate is appropriate before initiating second-line antimicrobials in a horse that has not responded to initial therapy, particularly when the drug in question carries a higher risk of adverse effects.

Laboratory involvement extends beyond culture and susceptibility. Acute phase protein measurement, serial blood gas analysis, and cytological evaluation of tracheal aspirates or bronchoalveolar lavage fluid can distinguish bacterial from non-bacterial inflammation and monitor response. Antimicrobial susceptibility testing should include drugs relevant to the equine respiratory tract, and the laboratory should be informed of the clinical context so that appropriate panels are run.

Regulatory reporting obligations vary by jurisdiction. The FDA Center for Veterinary Medicine provides information on adverse event reporting for approved animal drugs, and the AVMA antimicrobial stewardship resources outline professional expectations for judicious use. Extralabel use of drugs not approved for horses, or use of drugs prohibited in food-producing animals, carries specific reporting and record-keeping requirements that the prescribing veterinarian must know before dispensing. The World Organization for Animal Health terrestrial standards address international expectations for antimicrobial use monitoring and resistance surveillance, which increasingly influence national policy.

Frequently Asked Questions

How Should I Manage Antimicrobial Therapy When Culture and Susceptibility Testing Are Not Feasible?

When sampling is impractical due to financial constraints or patient instability, base the initial choice on expected pathogens, local resistance patterns, and drug pharmacokinetics. Trimethoprim/sulfonamide combinations have historically been useful for equine respiratory infections, but absorption varies between individual horses and with feed intake, so clinical response must be assessed carefully. If the horse fails to improve within 48 to 72 hours, revisit the diagnosis, obtain samples before changing drugs, and broaden the differential list. Document the rationale for empirical therapy and the planned reassessment date in the medical record. Regional antibiograms, where available, should guide empirical selection more reliably than anecdotal experience.

What Are the Minimum Records I Should Keep for Antimicrobial Use in Respiratory Cases?

Record the clinical indication, the drug and dose prescribed, the route and duration, and the basis for the decision, whether culture results, cytology, or a working diagnosis. Note the planned review date and the criteria that would trigger a change in therapy. This documentation supports later audit of prescribing patterns and helps identify cases where antimicrobials were continued without clear benefit. The AVMA antimicrobial stewardship resources emphasize that measuring and reviewing antibiotic use is a core component of responsible prescribing. In practices without formal audit systems, a simple quarterly spreadsheet of respiratory cases and antimicrobial prescriptions provides a starting point for identifying overuse.

How Do I Approach Antimicrobial Stewardship When the Owner Expects Antibiotics for a Viral Cough?

Explain that most acute viral respiratory infections in adult horses resolve with supportive care alone, and that antimicrobials do not shorten the course or reduce viral shedding. Describe the specific harms of unnecessary antibiotics, including disruption of normal flora, selection of resistant organizms, and the risk of complicating a future bacterial infection. Offer a concrete monitoring plan with defined parameters, such as temperature, appetite, and respiratory rate, and specify the threshold for re-evaluation. If the owner remains anxious, schedule a follow-up examination in 48 to 72 hours instead of prescribing prophylactically. This converts the expectation into a structured clinical plan.

What Should I Do When a Horse Is Not Responding to the Initial Antimicrobial Choice?

First confirm that the drug is being administered correctly and that the horse is absorbing it, since oral absorption of some antimicrobials is variable in horses. Re-examine the horse and repeat thoracic ultrasonography or radiography if pneumonia or pleuropneumonia was the working diagnosis. Collect tracheal wash or bronchoalveolar lavage samples for cytology and culture before changing drugs. Consider complications such as pulmonary abscessation, pleural loculation, or a foreign body. If the horse has deteriorated despite appropriate therapy, reassess for a nonbacterial cause such as viral infection, equine asthma, or neoplasia. The presence of multidrug-resistant organizms, including Acinetobacter baumannii, has been documented in equine lower respiratory tract infections, and susceptibility testing is essential in nonresponders.

How Does Stewardship Differ in a Hospital Setting Compared with Ambulatory Practice?

Hospitalized horses require additional attention to infection prevention because nosocomial transmission of resistant organizms is a recognized problem. Acinetobacter baumannii has been associated with equine thrombophlebitis and lower respiratory tract infection, and such isolates are often multidrug resistant. In the hospital, culture and susceptibility testing should be performed earlier, isolation protocols applied when respiratory pathogens are suspected, and daily antimicrobial review integrated into rounds. Ambulatory practice allows more flexibility for observation without antimicrobials, but follow-up may be less reliable. In both settings, the same decision framework applies: confirm bacterial infection, choose the narrowest effective drug, and define the duration before the first dose is given.

How Should I Discuss Antimicrobial Resistance Risk with Clients Who Board Multiple Horses?

Frame the discussion around the shared respiratory health of the group instead of the individual horse alone. Explain that antimicrobial use in one horse can select for resistant bacteria that may spread to other horses through shared airspace, water sources, or handling equipment. Emphasize that reducing antimicrobial use in viral outbreaks preserves drug effectiveness for the bacterial pneumonia that may follow. Recommend biosecurity measures such as separating coughing horses, dedicated feeding equipment, and hand hygiene between horses. The WOAH terrestrial animal health standards provide a framework for disease prevention that reduces the need for antimicrobial treatment at the population level. This approach aligns client interests with stewardship goals.

Related Clinical & Scientific Guides

• Veterinary Formulary Essentials: Navigating Drug References
• Drug Interactions with Antiepileptic Drugs in Veterinary Patients: Managing Polypharmacy
• Drug Interactions with Corticosteroids in Veterinary Patients: A Comprehensive Review

References and Further Reading

• A quarterly Survey of antibiotic prescribing in small animal and equine practices-Minnesota and North Dakota, 2020.. 2022.
• A comprehensive review on the antiviral activities of chalcones.. 2021.
• Trimethoprim/sulfonamide combinations in the horse: a review.. 1994.
• Thinking Outside the Bug: Targeting Outer Membrane Proteins for <i>Burkholderia</i> Vaccines.. 2021.
• Acinetobacter in veterinary medicine, with an emphasis on Acinetobacter baumannii.. 2019.
• Update on viral diseases of the equine respiratory tract.. 2015.
• FDA Center for Veterinary Medicine: Animal Drug Information. FDA CVM.
• AVMA Antimicrobial Use and Stewardship. American Veterinary Medical Association.
• MSD Veterinary Manual, Professional Edition. MSD Veterinary Manual.

Related Articles

• Antimicrobial Stewardship in Equine Practice: Challenges and Solutions
• Antimicrobial Stewardship in Respiratory Infections of Dogs and Cats
• Antimicrobial Stewardship in Canine Periodontal Disease: Antibiotic Use in Dentistry
• Antimicrobial Stewardship in Feline Respiratory Infections: When Antibiotics Are Needed
• Antimicrobial Stewardship in Food Animals: Principles and Practical Application

This article is educational professional reference material for veterinary audiences. It is not a substitute for veterinary diagnosis, individual clinical judgment, current product labeling, or applicable regulatory requirements.