Study supports more selective antibiotic use in foal pneumonia
Bottom line
Version 1
A new cohort study in The Veterinary Journal suggests equine practitioners may be able to treat foal bronchopneumonia more selectively without compromising outcomes. Researchers followed 1,200 warmblood foals on a single stud farm across the 2020, 2022, 2023, and 2024 foal crops and compared a more aggressive treatment threshold with a more conservative one based on lesion size on thoracic ultrasound. Under the conservative approach, the share of foals receiving antimicrobials fell from 29.0% to 17.5%, while mortality, treatment failure, and recurrence did not increase. The findings land amid growing concern about antimicrobial resistance in Rhodococcus equi and other causes of foal pneumonia, where widespread early treatment has been criticized for exposing many mildly affected foals to macrolides and rifampin unnecessarily. (sciencedirect.com)
Why it matters: For veterinary professionals, the study adds field evidence to support antimicrobial stewardship on breeding farms that routinely screen foals for subclinical pneumonia. That’s important because experts have warned that treating every ultrasonographic lesion can drive resistance without clear clinical benefit, and current guidance already discourages prophylactic antimicrobial use in at-risk foals. In practice, the paper may give veterinarians more confidence to reserve treatment for foals with more advanced lesions or clearer evidence of clinically significant disease, while continuing close monitoring of those managed conservatively. (sciencedirect.com)
What to watch: Expect discussion over whether these single-farm results can be replicated on other endemic farms, and whether they will further shift screening and treatment protocols toward tighter, stewardship-focused thresholds. (sciencedirect.com)
Version 2
A newly published study in The Veterinary Journal is adding weight to a message many equine clinicians have been wrestling with for years: less antibiotic use in foals with bronchopneumonia may sometimes be the better course. In a cohort of 1,200 warmblood foals from one stud farm, researchers found that delaying antimicrobial treatment until pulmonary lesions were more advanced reduced antibiotic exposure substantially, without worsening mortality, treatment failure, or recurrence. (sciencedirect.com)
The issue sits within a longer debate over how aggressively to manage presumed Rhodococcus equi pneumonia on endemic farms. Routine thoracic ultrasound screening has helped identify subclinical disease earlier, but it has also led to treatment of foals that might never have progressed to clinically important illness. Reviews and guidance documents have noted that this approach can increase antimicrobial use and may contribute to the emergence of macrolide- and rifampin-resistant R. equi. (pubmed.ncbi.nlm.nih.gov)
According to the study, investigators evaluated foals born in 2020, 2022, 2023, and 2024 and diagnosed with bronchopneumonia through a screening program. They compared outcomes between earlier years using a lower threshold for treatment and later years using a more conservative threshold tied to larger pulmonary lesions. Antimicrobial use dropped from 29.0% of foals in 2020/2022 to 17.5% in 2023/2024. At the same time, the paper reported no meaningful increase in mortality, and no worsening in treatment failure or recurrence under the conservative protocol. (sciencedirect.com)
That result aligns with broader stewardship messaging in equine medicine. In The Horse, Stacey Oke, DVM, MSc, described growing concern that selective treatment strategies are needed to preserve antibiotic effectiveness while still protecting foals from R. equi pneumonia. Educational material from UC Davis similarly notes that, without definitive diagnosis, some unaffected foals may be treated unnecessarily, adding to resistance pressure. Merck Veterinary Manual also advises against prophylactic antimicrobial treatment in at-risk foals. (thehorse.com)
Industry attention to resistance is increasing for good reason. Recent surveillance and review literature describe emerging multidrug-resistant R. equi as a serious threat in breeding operations, especially where macrolide-rifampin combinations have been used heavily over time. While the new study was not a randomized, multi-site trial, it offers practical farm-level evidence that more restrained treatment thresholds may reduce selection pressure without sacrificing outcomes, at least in a closely monitored screening environment. That’s an important distinction: the success of conservative treatment likely depends on disciplined follow-up, consistent ultrasound protocols, and rapid intervention when lesions progress. (pmc.ncbi.nlm.nih.gov)
Why it matters: For equine veterinarians, the study supports a more nuanced conversation with breeders and pet parents about when antibiotics are truly necessary. On farms that screen aggressively, the default response to every lesion may no longer be defensible if similar outcomes can be achieved with fewer treated foals. Reducing unnecessary macrolide and rifampin exposure could help preserve treatment options for the foals that are genuinely sick, while also lowering drug costs, handling burden, and the downstream risk of resistant organisms becoming entrenched on a farm. (sciencedirect.com)
The findings should still be interpreted carefully. This was a single-stud-farm cohort, and bronchopneumonia in foals is not synonymous with confirmed R. equi infection in every case. Farm management, pathogen pressure, screening cadence, and case selection all influence whether a conservative protocol is safe. Even so, the paper strengthens the case for stewardship-minded protocols that rely on monitoring and escalation, rather than reflexive early treatment. (sciencedirect.com)
What to watch: The next question is whether similar protocols will be validated across multiple farms and incorporated into broader equine practice guidance, especially as concern over resistant R. equi continues to grow. (pubmed.ncbi.nlm.nih.gov)