Short communication: Anesthetic residues in milk after topical application during treatment of hoof lesions in dairy cows

Abstract

Hoof lesions in dairy cows are usually treated by trimming the hoof. However, trimming by itself can cause severe pain or exacerbate already existing pain. Hoof trimming is usually not carried out by trained veterinarians, and pain management is not provided. Pain control during trimming is not only an ethical obligation but also allows for better manipulation and more meticulous treatment. Tri-Solfen (Bayer Animal Health, Pymble, Australia) is a spray gel containing lidocaine, bupivacaine, and cetrimide that is easily applied topically and has demonstrated pain-mitigation effects during and after hoof trimming. In the European Union, these local anesthetics are not approved for use in food-producing animals because of a lack of residue data and concerns about genotoxic effects in cattle and humans. The aim of this study was to assess lidocaine, bupivacaine, and 2,6-xylidine residues in milk after Tri-Solfen application in dairy cows. Five dairy cattle in the dry-off period were enrolled in the study based on clinical evidence of lameness (score ≥3 on a 5-point scale). After cleaning and superficial trimming, we applied 3 to 14 mL of Tri-Solfen to the lesions before continuing treatment. Two milk samples were collected per animal in the following 4 milkings and analyzed in a reference laboratory. Residues of lidocaine above the limits of quantification (0.2 µg/L) were found in milk samples in the first milking 6 h after treatment in only 2 cows. This study shows that excretion of local anesthetics and their metabolites in milk after topical application of Tri-Solfen is negligible and even undetectable after the first milking 6 h post-treatment.