Presurgical acetone and chlorhexidine aseptic preparation of the equine hoof lowers bacterial counts below surgically acceptable threshold.

Overview

• This study investigated whether applying acetone and chlorhexidine to the equine hoof after removing the outer hoof wall can sufficiently reduce bacterial contamination to levels suitable for surgery.
• It also tested whether a special neutralizing broth (Dey-Engley neutralizing broth, DENB) can effectively neutralize chlorhexidine residues in hoof tissue samples.

Background

• Equine hooves can harbor bacteria that pose a risk for infections during surgical procedures.
• Effective presurgical aseptic preparation is crucial to lower bacterial counts to safe levels.
• The researchers aimed to verify a disinfection protocol involving acetone and 4% chlorhexidine solutions and quantify their effect on bacterial load.
• Additionally, they evaluated the capacity of DENB to neutralize leftover chlorhexidine during bacterial culture analysis, which is important to accurately assess remaining bacteria.

Methods

• Clinical prospective study design involving 24 horse hooves.
• The superficial hoof wall was mechanically removed to expose deeper tissue.
• Disinfection steps included:
  • Application of acetone.
  • 5-minute preparation using 4% chlorhexidine, including both rough and aseptic methods.
• Samples were aseptically taken from three hoof locations before and after disinfection:
  • Dorsal wall
  • Frog (a soft part of hoof)
  • Sole
• Samples were minced and incubated either in Dey-Engley neutralizing broth (DENB) or saline.
• Serial dilutions were plated on blood agar and incubated for 48 hours to count aerobic bacterial colonies.
• Statistical models (linear and logistic regression mixed models) were used to analyze the effects of:
  • Disinfection treatment
  • Neutralizing broth treatment
  • On log10 colony-forming units per gram of tissue (CFUs/g) for each hoof site

Results

• The combination of acetone and chlorhexidine significantly reduced bacterial load across all sampled sites when considering the interaction effects of site and disinfection.
• Adjusted mean bacteria counts (log10 CFUs/g) ranged from:
  • 3.24 (lowest)
  • 4.76 (highest)
• Proportion of samples reduced below the surgical acceptable threshold (5 log10 CFUs/g):
  • Dorsal wall: 66.7%
  • Frog: 62.5%
  • Sole: 25%
• Before disinfection, bacterial counts were similar whether samples were incubated in DENB or saline.
• After disinfection, samples incubated in DENB showed higher CFUs/g than those in saline, indicating DENB effectively neutralized residual chlorhexidine that would otherwise suppress bacterial growth in cultures.

Conclusions

• The acetone and 4% chlorhexidine protocol is effective at reducing bacterial contamination on equine hooves to levels generally considered surgically acceptable, especially on the dorsal wall and frog areas.
• Sole tissue showed less reduction, possibly due to its anatomical or microbial characteristics.
• Dey-Engley neutralizing broth proved to be a reliable agent for neutralizing residual chlorhexidine in tissue samples, ensuring accurate bacteriological assessments.
• This disinfection protocol and neutralization method can improve surgical site preparation and diagnostics in veterinary practice for horses.