The effect of selective dry cow therapy on new intramammary infections and the bacterial diversity of quarter milk

The present study aimed to evaluate the effect of selective dry cow therapy (SDCT) (protocol 1: antimicrobial combined with ITS; vs. protocol 2: internal teat sealant (ITS) without antimicrobial) on the bacterial diversity of quarter milk. Milk quarter samples (n = 60) were collected on the day of drying-off and on days 7 and 14 postpartum (Holstein cows' lactation <3 and DIM <450). Based on the results of bacteriological culturing, the quarters were categorized as healthy, cured, persistent, and new intramammary infection. The milk sample of the quarter was submitted to bacteria DNA extraction in order to evaluate the effect of antibiotic usage for dry-off on the microbiome. Overall, healthy cows treated with SDCT protocol using only teat sealant no altered bacterial diversity in comparison to cows treated with antibiotics.