Effect of erythromycin and colistin ophthalmic ointment on post-race keratitis in Thoroughbred racehorses.

Overview

• This study evaluated whether applying an ophthalmic ointment containing erythromycin and colistin immediately after horse races could prevent post-race keratitis (an eye inflammation) in Thoroughbred racehorses.
• The research compared keratitis rates between horses receiving eye flushing only and those given eye flushing plus the antibiotic ointment after races on turf and dirt tracks.

Background and Purpose

• Post-race keratitis is an inflammation of the cornea that occurs in horses after racing, potentially affecting eye health and performance.
• The study aimed to determine if administering an ophthalmic ointment containing erythromycin and colistin (referred to as EC ointment) after races would lower incidence rates of keratitis.
• Two main comparisons were made:
  • Between groups that received no ointment (eye flushing only) and groups that received EC ointment after races.
  • Between groups given a non-antimicrobial ointment (white petrolatum) versus groups given the antimicrobial EC ointment.
• These comparisons were analyzed separately for races run on turf tracks and dirt tracks, as environmental factors may differ.

Study Methods

• Thoroughbred racehorses were monitored following races on two different surfaces: turf and dirt.
• Horses were sorted into treatment groups:
  • Non-ointment group: eye flushing only after races.
  • Ointment group: eye flushing followed by application of EC ointment.
  • Subgroups for random assignment:
    • Non-antimicrobial ointment group (white petrolatum application).
    • Antimicrobial ointment group (EC ointment application).
• Incidences of post-race keratitis were recorded and statistically compared between groups for both turf and dirt race conditions.

Key Results

• After turf races:
  • Keratitis incidence was significantly higher in horses that received only eye flushing (6.25%) compared to those treated with EC ointment (0.55%).
  • Among the randomly assigned ointment subgroups, the non-antimicrobial group had an 8.18% incidence, while the antimicrobial (EC ointment) group had 0%, showing a clear protective effect.
• After dirt races:
  • No significant difference was observed in keratitis incidence between the non-ointment (0.56%) and ointment (0.53%) groups.
  • Similarly, no significant differences were found between non-antimicrobial (1.87%) and antimicrobial (1.41%) ointment groups.

Interpretation and Conclusions

• Applying the EC ointment after turf races substantially reduced the incidence of post-race keratitis, suggesting a beneficial prophylactic effect.
• The lack of significant difference after dirt races indicates that environmental or pathophysiological factors differ on dirt tracks, or that keratitis after dirt races may have different causes less responsive to antibiotics.
• The results point toward a bacterial component in the development of keratitis following turf races, given the effective reduction after application of antimicrobial ointment.
• However, the study notes limitations:
  • Limited microbiological and cytological testing was conducted, so direct identification of the causative bacteria was not achieved.
  • The exact pathogenesis of post-race keratitis remains unclear, and further lab testing is needed to confirm bacterial involvement and potentially guide targeted treatment.
• Overall, the study suggests that routine use of EC ointment after turf races is effective in reducing eye inflammation but may not be necessary or beneficial after dirt races.