Using salicylic acid to treat Digital Dermatitis in dairy cows

Salicylic acid is an organic acid found in willow bark and is most widely known as the precursor to acetyl salicylic acid, otherwise known as Aspirin.

Salicylic acid is keratolytic, promoting the removal of epidermis and so has been found to be very effective for treating digital dermatitis, particularly the proliferative (hairy) and hyperkeratotic (warty) stages. The low pH may also make it bacteriocidal, particularly as the spirochaetes causing digital dermatitis are largely unviable at below pH 5.

Salcylic acid is widely used, especially by hoof trimmers. However, care is required to stay the right side of the law.

The rules on use of medicines can be confusing, for vets as well as for farmers and hoof trimmers. In the UK only a veterinary surgeon is permitted to diagnose, advise on treatments and prescribe medicines under the Veterinary Surgeons Act (1966). The VSA is a good read if you ever suffer from insomnia – which can be found here. The Veterinary Medicines Directorate (VMD) keep a list of licensed medicines and their withdrawal periods. People making any treatment claims with unlicensed products can expect to be challenged by the VMD. So where does that leave us with salicylic acid for the treatment of digital dermatitis?

1. Professional foot trimmers must follow the guidance of the local (prescribing) veterinary surgeon to be legally compliant. In practice this means using the products provided by the farmer, who in turn has had them prescribed by the vet. Treatment protocols should be documented in treatment plans.
2. There are several antibiotic spray treatments licensed for digital dermatitis, including chlortetracycline spray (Cyclospray), oxytetracycline spray (Engemycin, Terramycin, Alamycin) and Thiamphenicol (TAF spray). As with all licensed veterinary medicines, the vet must advise and prescribe these.
3. If antibiotic treatments are to be avoided, there is a licensed chelated copper and zinc treatment for digital dermatitis – Intracare Hoofit Gel. In a recent German trial the gel (used with a bandage) was found to be as effective as an antibiotic spray. However, note the debate about using bandages is not resolved and this will be a subject for another newsletter for sure.
4. Under certain circumstances, vets can advise and prescribe un-licensed efficacious treatments using the “cascade”. There must always be a justification for using something which is not licensed. Reducing antibiotic usage and choosing a treatment more efficacious for hyperkeratotic lesions could be a sound justification. A crucial consideration is whether the active ingredients are permitted for use in food producing animals. Salicylic acid is on the VMD’s “List of Allowed Substances”, even though it does not have a licence for treatment of digital dermatitis, so it could be used under the cascade rules. However, when used under the cascade it carries a minimum 7-day milk withhold period and 28-day meat withdrawal period.

So whilst the situation is quite restrictive currently, we do anticipate that a licensed salicylic acid product will become available for use in the UK in the near future, which will then make life for the prescribing vet and trimmer so much simpler and exciting. Until then we should apply the tools we have as best as we can.