24 Aug 2025
Phil Elkins BVM&S, CertAVP(Cattle), MRCVS looks at the latest information on the causes, prevention and treatment of this issue
Phil Elkins
Job Title
Image: Fredy Thürig/ Adobe Stock
Bovine respiratory disease (BRD) remains a significant and, at times, daunting health challenge in both beef and dairy herds worldwide.
Despite decades of research and the advent of advanced diagnostics, BRD continues to inflict heavy economic and welfare costs – an estimated £50 million in the UK alone1. This complex syndrome encompasses a spectrum of upper and lower respiratory tract infections, often indistinguishable on clinical grounds, and demands an integrated approach to control.
This review will recap the disease, while considering the latest peer-reviewed insights on BRD’s multifactorial aetiology, evidence-based prevention strategies and evolving treatment paradigms.
BRD is not a single disease entity, but a syndrome arising from the interplay of pathogens, host immunity and environmental stressors. Clinical signs – ranging from fever, cough, and nasal discharge to tachypnoea and depression – offer limited specificity and cannot reliably pinpoint the causative agents1.
Primary viral infections frequently prime the respiratory tract for secondary bacterial invasion. The usual suspects include:
These viruses compromise mucociliary clearance, induce epithelial damage and dysregulate local immunity, setting the stage for bacterial overgrowth and pneumonia2.
Among bacterial pathogens, four species dominate BRD pathology:
These organisms are often commensals of the nasopharynx, but become opportunistic in the lower tract when host defences wane.
Molecular surveys confirm that their relative abundance in the nasal microbiome correlates with clinical disease, although thresholds vary by herd and environment3.
This makes interpretation of qualitative assays fraught with issues. The presence of a pathogen in a nasopharyngeal sample may not be indicative of causality. However, presence in a high quantity is likely significant.
Experimental and field data underscore the complexity of pathogen interactions. The classical model – primary viral insult followed by bacterial superinfection – is well supported, but other scenarios, such as simultaneous viral-viral or bacterial-bacterial co-infections, can exacerbate disease severity.
In vitro studies show that viral priming enhances bacterial adhesion, while certain bacterial combinations synergise to deepen lung lesions in calves. This nuanced understanding challenges one size fits all treatment and prevention approaches2.
It also raises questions when creating vaccination protocols on farm: is it more important to control the apparent primary agent, or the secondary pathogen which is significantly exacerbating case severity? It is not always feasible, or financially acceptable to the farmer, to tackle both.
Host susceptibility hinges on immune maturation, stress, and nutritional status. Key risk factors include:
Collectively, these elements create a fertile ground for BRD outbreaks. Ensuring adequate colostrum quality and management, minimising overcrowding and employing low-stress handling techniques are cornerstone measures to bolster calf resilience2.
The clinician is not short of options to prevent BRD, rather than just facing having to treat it. Unsurprisingly, as with many other diseases, the prevention of BRD is almost always more rewarding than treating diseased individuals.
A multi-pronged approach to prevention will often reap the best rewards, with improvements from each measure being additive.
Improved biosecurity and calf management can lead to significant improvements in disease transmission, and as such reduce the prevalence of BRD.
Robust passive immunity starts with maternal colostrum containing high immunoglobulin G concentrations.
Poor colostrum management or delayed feeding increases BRD susceptibility. Likewise, balanced micronutrients (zinc, vitamin E and selenium) underpin mucosal barrier integrity and leukocyte function.
It also follows logically that energy or protein deficiency in calves leads to weakened immune systems that are predisposed to clinical disease. If animals are not achieving target daily liveweight gains, nutrition may be playing a role in disease.
Strategic vaccination against viral and bacterial BRD agents is widely endorsed but under utilised. A recent consensus paper highlights common barriers: visible disease absence, antibiotic preference, maternal antibody interference and scepticism over efficacy.
To overcome these, veterinarians should:
Vaccination rates for BRD have increased in the UK from 29% in 2011 to 42% in 2021, which is cause for some positivity. However, given the prevalence of BRD, it does show a need for further uptake4.
Early and accurate diagnosis is pivotal to targeted interventions and antibiotic stewardship.
Traditional detection relies on pen-check scoring systems (for example, DART, or, depression, appetite, respiratory tract, temperature) or standardised composite scoring systems, such as the Wisconsin calf score.
However, sensitivity hovers around 60% to 70%, leading to both under and over treatment. Portable thoracic ultrasonography (TUS) offers a leap forward – studies report higher than 90% accuracy for detecting consolidations unseen at gross examination – and can be deployed on farm for real-time decision making5.
TUS is used extensively in other countries with large units, where dedicated staff members can be appropriately trained to undertake the procedure quickly and accurately. The opportunities in the UK for this are more limited, and as such more reliance may occur on combining other diagnostic modalities for early detection.
An increasing range of animal monitoring solutions are available for automated identification of adverse health events in calves. These rely on a variety of individual parameters, often combined to derive an animal norm, with deviations from this likely significant. Using these in combination shows some promise for improved sensitivity, while also detecting disease earlier6.
Emerging field-based molecular assays, such as recombinase-aided amplification for BRSV RNA, deliver results within 20 minutes and rival laboratory reverse transcription PCR in specificity.
Biomarkers such as serum haptoglobin, fibrinogen and nasopharyngeal acute-phase proteins are also under investigation as adjuncts to clinical assessment. Machine-learning models integrating pathogen abundance, animal demographics and environmental data are on the horizon, promising to refine predictive accuracy beyond human capability5.
Effective management of BRD hinges on timely therapeutic choices balanced against antimicrobial-resistance concerns.
Long-acting macrolides (for example, tulathromycin or gamithromycin) and florfenicol dominate metaphylaxis and first-line treatment protocols. Other antimicrobials such as beta-lactams or tetracyclines remain useful at times, while fluoroquinolones are reserved for multi-resistant pathogens.
Antimicrobial selection should be guided by culture and sensitivity testing whenever feasible to limit broad-spectrum use, and by response to treatment where culture and sensitivity is not feasible.
NSAIDs such as flunixin meglumine and meloxicam reduce fever, alleviate pulmonary inflammation and improve feed intake.
Repeated treatments of NSAIDs can help to ensure continued, smooth recovery from disease.
Adjunct approaches – including probiotics, phytogenics and immune modulators such as cytokine-enhancing nutraceuticals – are under investigation to reduce reliance on conventional drugs.
Preliminary data suggest modulation of the respiratory microbiome and immune priming can lower BRD incidence, but field-scale trials are needed.
Despite substantial progress in dissecting BRD’s complex aetiology, real-world control remains elusive.
Bridging the gap between research and practice demands:
Vigilant surveillance, ongoing education and collaborative veterinary–producer partnerships are the cornerstones of sustainable BRD control.
As new tools emerge, the veterinary community must remain agile – embracing evidence, challenging assumptions and prioritising animal welfare – to help tip the balance towards control of a disease complex which has been high on the agenda for years.
