Bovine respiratory disease (BRD) continues to be a leading cause of morbidity and mortality in both dairy and beef cattle and represents a major driver of antimicrobial use in the industry. For practitioners, accurate case diagnosis is often complicated by the multifactorial nature of BRD, the variability of clinical signs and the limitations of common sampling approaches.
There are a number of tools out there for veterinarians working with respiratory disease, including subjective clinical illness scores and necropsy data. Dr. Jenna Bayne from the Auburn University College of Veterinary Medicine reminds us that while it may be difficult to hear much through a stethoscope over the sound of hydraulic chutes and noisy fans, “the art of a good, thorough physical exam should not be forgotten.”
Using non-invasive tools, such as thoracic ultrasound, may be beneficial for identifying which animals could be best for more invasive — and perhaps more costly — diagnostic techniques.
While deep nasal swabs have their place, understanding their limitations and best use cases is important. Transtracheal washes (TTW) and bronchoalveolar lavages (BAL) are valuable diagnostic tools that provide direct access to the lower respiratory tract. By generating samples that are less confounded by commensal flora than nasal swabs, they allow veterinarians to more accurately identify etiologic agents and guide evidence-based therapeutic decisions. While both TTW and BAL share a similar goal, their applications, benefits and practical considerations differ.
Diagnostic Techniques
Transtracheal Wash:
TTW is performed by passing a sterile catheter to the lower airways through an incision in the trachea. After instilling a small volume of sterile saline, fluid is aspirated and collected for analysis. Samples typically represent the trachea and bronchi, offering clinically useful information with minimal equipment. TTW can be performed on adult cattle chute-side with the animal standing restrained and on lightly sedated calves positioned in sternal recumbency.
Bronchoalveolar Lavage:
BAL requires more specialized equipment, such as an endoscope or a cuffed BAL catheter, which is passed into the trachea and guided down into a bronchus. Once the catheter is wedged in place, saline is instilled and aspirated, retrieving a sample directly from the alveolar spaces. This technique is particularly useful for diffuse or interstitial lung diseases.
If you think you may be using both techniques for sample collection, start with the TTW so you don’t contaminate the lower airways — which could happen when passing the BAL tube through the nose and into the trachea.
Advantages over Alternate Methods
Other methods, such as nasal or pharyngeal swabs, are inexpensive and non-invasive, but primarily recover upper respiratory flora — which may not correlate with pathogens in the lungs. TTW and BAL samples reflect the lower respiratory tract, improving diagnostic accuracy.
And while post-mortem examination remains the gold standard for characterizing BRD, it is retrospective. TTW and BAL permit antemortem sampling and allow practitioners to intervene therapeutically.
At the same time, coughing, nasal discharge, fever and depression are non-specific and cannot differentiate between bacterial, viral or non-infectious causes. Cytology and culture from TTW or BAL add objective laboratory data to refine diagnosis.
How to Choose Your Diagnostic Methods
You may wonder when TTW or BAL could be beneficial compared to a deep nasal swab. When will an upper respiratory tract sample suffice? Can we use an upper tract sample to make interpretations or decisions for lower respiratory disease?
According to Bayne: “It depends on what we’re asking as far as the clinical question. Is this an individual animal, or am I given a good representative sample of multiple calves and using deep nasal pharyngeal swabs — which do have good agreement at the herd level — with lower respiratory tract sampling methods? It’s not to say that you need to always use a transtracheal wash. But in the very refractory cases, if you need culture and susceptibility results or you’re struggling with responsive therapy, maybe you need to go deeper into the lungs and get the most valid sample.”
Clinical and Herd Applications
For practicing veterinarians, TTW and BAL can support antimicrobial therapy by linking culture and sensitivity results to pathogens recovered from the lung. These techniques can also aid outbreak investigations by identifying circulating pathogens within a group and contribute to antimicrobial stewardship by dictating drug selection.
At the herd level, TTW is often the more pragmatic option, while BAL is frequently reserved for referral cases, research trials or complex clinical scenarios where deeper sampling is warranted.
Respiratory diagnostics in cattle will demand tools that go beyond clinical impression and superficial sampling. TTW and BAL provide practitioners with direct, antemortem access to the lower respiratory tract — supporting more accurate diagnoses, guiding rational antibiotic use and ultimately improving animal outcomes. While TTW is typically the more accessible option for field practitioners, both techniques have distinct advantages and limitations. But when used judiciously, they can significantly elevate the quality of respiratory diagnostics in cattle practice.
Practical Tips for Practitioners
Animal Selection & Restraint
- Choose animals in the early stage of disease for best diagnostic yield
- Adequate chute restraint is essential. Cross-tie to stabilize the head
- Position the head higher for a TTW to expose the neck and more horizontally for a BAL
Aseptic Techniques
- Use sterile gloves, catheters and syringes
- Avoid touching catheters as they are introduced
- TTW: Clip and surgically prep the neck area to reduce contamination
Sample Collection & Handling
- TTW: Introduce and immediately aspirate 30 mL to 50 mL of sterile saline
- BAL: Use 0.2 mL/kg to 0.3 mL/kg of sterile saline
- Submit promptly for culture, molecular diagnostics and/or cytology
- Keep samples chilled but not frozen
Aftercare
- Monitor cattle after the procedure for signs of swelling, emphysema or distress
- TTW sites should be checked for infection or leakage
- Observe animals until any sedation has fully worn off
