Everyone is familiar with COVID prevention protocols that encourage frequent hand washing and/or use of alcohol-based rubs (ABR) for antisepsis. Previous studies in horses have demonstrated that a 90 second use of ethanol on the jugular furrow and propanol on the abdomen were not only well tolerated but also reduced bacterial colony-forming units.
Concerns over antimicrobial resistance possibilities to 2-4% chlorhexidine gluconate (CHG) stimulated a research project that evaluated the use of ABR—80% ethanol (ET)—on the distal limb, which is known to carry high burdens of bacteria. The research objective was to identify alternatives for antisepsis as a substitute for CHG.
The study compared the use of 90-second application of ET to the standardly used CHG three- to-five-minute scrub on distal limbs that alternates CHG with isopropyl alcohol or water rinse [Doyle, A.J.; Saab, M.E.; Lewis, K.M.; McClure, J.T. Comparison of chlorhexidine and alcohol-based antisepsis of the distal limbs of horses. Equine Veterinary Journal Dec 2020; doi: 10.1111/evj.13417].
Sites on the distal limbs were clipped in almost all the horses except for one treatment group (d). Then forty-one horses were separated into specific treatment groups: a) five-minute scrub with 4% CHG followed by sterile saline rinse; b) 90-second scrub with 80% ethanol that was allowed to evaporate and no rinse; c) 90-second spray with 80% ethanol with no mechanical scrub or rinse; or d) 90-second spray with 80% ethanol to an unclipped site with no mechanical scrub or rinse.
Prior to and following treatment, bacterial loads were measured. Colony-forming units taken from the distal limbs pre-treatment did not vary between fore or hind limbs.
“This study showed that 80% ethanol applied as a 90-second scrub to a clipped site on the distal limb of horses is not significantly different than the applied CHG antiseptic protocol at reducing bacterial count,” noted the authors.
Although there was no difference in bacterial reduction in CHG and ET applied to unclipped sites on the forelimbs, the alcohol-based antisepsis had less efficacy on unclipped hind limbs. Researchers have no definitive reason for that other than speculation that the hind limbs have different bacterial populations and/or biofilm production.
For short-term procedures, the authors summarized: “This study showed no significant difference in the reduction of bacterial counts on the distal limb of horses between CHG and 80% ethanol when applied as a scrub over a clipped site.”
Summarizing the differences between treatment groups, they recommend that “when using alcohol-based antisepsis in horses, apply the alcohol in a concentric wipe to a clipped site for a 90-second wet contact time. Applying alcohol as a spray, or to an unclipped site, had significantly lower reductions in colony-forming units than CHG in the hind limbs.”
It is important to note that this study only used ethanol-based alcohol and did not explore use of other products such as isopropyl alcohol or n-propanol.