Update on Bacterial Pneumonia in the Foal and Weanling Sarah M. Reuss, VMD a, *, Noah D. Cohen, VMD, MPH, PhD b INTRODUCTION Bacterial pneumonia is a common problem in foals of all ages. The causal agents of that pneumonia, however, vary with the age of the foal. Neonatal foals are more likely to have pneumonia as a component of systemic sepsis, whereas older foals and weanlings can have primary pneumonia. Knowledge of the likely agents is especially important when selecting empirical antimicrobials while awaiting microbial culture results. With appropriate treatment, prognosis for survival and athletic performance is good. ETIOLOGY Neonates Neonatal foals may acquire pneumonia as a primary condition, but are more likely to develop bacterial pneumonia secondary to sepsis, the major cause of morbidity and mortality in the neonatal foal. Infection may occur in utero because of ascending The authors have nothing to disclose. a Department of Large Animal Clinical Sciences, University of Florida College of Veterinary Medicine, PO Box 100136, Gainesville, FL 32610, USA; b Department of Large Animal Clinical Sciences, Texas A&M University College of Veterinary Medicine, 4475 TAMU, College Station, TX 77845, USA * Corresponding author. E-mail address: sreuss@ufl.edu KEYWORDS  Equine  Foal  Weanling  Pneumonia  Sepsis  Aspiration  Rhodococcus equi KEY POINTS  Bacterial pneumonia is a common cause of morbidity and mortality in foals of all ages.  The most likely causal agents of bacterial pneumonia vary with the age of the foal, and knowledge of likely agents and their antimicrobial-resistance profiles is important for treat- ment selection.  Macrolide antibiotics remain the treatment of choice for Rhodococcus equi infections, but resistance is emerging and effective alternatives are exiguous. Vet Clin Equine 31 (2015) 121–135 http://dx.doi.org/10.1016/j.cveq.2014.11.004 vetequine.theclinics.com 0749-0739/15/$ – see front matter Ó 2015 Elsevier Inc. All rights reserved.