Changing policy to treat foals with Rhodococcus equi pneumonia in the later course of disease decreases antimicrobial usage without increasing mortality rate.

Background: There is a lack of data on the efficacy of treatment of Rhodococcus equi pneumonia in association with an optimised selection of foals.

Objectives: To evaluate whether targeted treatment protocols resulting in decreased antimicrobial use impact foal mortality rates.

Study Design: Retrospective study.

Methods: Three hundred and thirty foals with pneumonia per year were randomly selected from 2008 to 2016. All foals were examined once weekly from birth until weaning. A physical examination of the respiratory tract, body temperature, haematology and an ultrasonographic examination of the lungs was included. Sonography areas with visible consolidation were measured and added to calculate an 'abscess score' which represents the extent of pulmonary damage. All weekly medical data were analysed retrospectively.

Results: In the period from 2008 to 2011, every foal with pulmonary abscesses was treated. The treatment protocol was changed in 2012 when only foals with larger lesions were treated. Between the two time periods 2008-2011 and 2012-2016, the abscess score at the beginning of treatment increased from a median of 4-11.5 cm. From all foals that developed R equi pneumonia, 81.5% received antibiotic treatment in 2008-2011 (n = 1215) compared with 50.9% in 2012-2016 (n = 1541). The percentage of foals that died from pneumonia or R equi infections did not differ significantly between 2008-2011 and 2012-2016 (0.4% vs 0.6% respectively; P = .6).

Main Limitations: There was some lack of clarity in old data because this was a retrospective study; therefore, some foals had to be excluded from data analysis.

Conclusions: Alteration of treatment criteria, to exclude antibiotic treatment of foals with smaller lesions, has significantly decreased the number of foals being treated without a significant increase in mortality from R equi pneumonia.