This study will develop, evaluate, and implement selective dry cow antibiotic therapy (SDCT). Udder health is the largest reason for antibiotic use on a dairy with half that expense being for dry cows. Historically blanket dry cow therapy (BDCT) was justified, but with advances in udder health management SDCT has potential to meet the public's expectation for judicious use. In year1 600 cows from a NYS dairy eager to help the industry develop protocols for prudent antibiotic use will be enrolled. Cows with less than 200,000 SCC on last test before dry and with less than 200,000 SCC average on the last three DHIA tests are at low risk for infection. All cows with stage 3 mastitis events or above these SCC cut-points will be treated with dry cow therapy (DCT) as they are at high risk for an infection. Cows at low risk will be randomly allocated to BDCT or internal teat sealant only. Milk samples will be obtained at dry date and at 3 days in milk. Statistical models will be used to compare first-test linear score and milk production, risk of culling, and risk of mastitis in the first 60 DIM. We expect that SDCT is not different from BDCT. For similar dairies, this will decrease dry cow antimicrobial use by 60%, reducing operational expenses, with almost no implementation cost, and lowering risks of antimicrobial resistance and residues. Based on the results of this applied research we will develop educational materials to implement this on other similar dairy farms in year 2 of this project.