September 2021

Drug resides in milk and clinical efficacy

Salicylic acid (SA) provides similar treatment efficacy to tetracycline-class antibiotic drugs for the treatment of digital dermatitis (DD) in dairy cows. No milk withholding time following SA treatment has been established in the United States. The objective of this study was to generate data about drug residues in milk following topical treatment of DD lesions with SA. Cows with active (M2 stage) DD lesions were assigned to 1 of 3 treatments: salicylic acid paste, salicylic acid powder, or tetracycline powder. Lesions were photographed digitally and thermographically and scored using the M-stage scoring system before treatment and at 7 and 28 d post-treatment. Milk samples were collected before treatment and at 4 h, 8 h, 24 h, 36 h, and 48 h afterward. Most cows did not have detectable salicylic acid in their milk more than 24 hours after treatment; however, 3 cows had detectable levels of SA at 36 hours post treatment. Treatments did not differ in their effects on DD lesions. These data suggest that milk from treated cows should not be used or sold for at least 48 hours following the topical treatment of DD lesions with salicylic acid.

Kelsey M. Wirt, Jennifer M. Young, Gerard Cramer, Sarah A. Wagner