The objectives of this study were: to investigate the microorganisms that cause subclinical mastitis in meat-producing sheep, to define cut-off points for two indirect diagnostic methods, to compare the cure rates for subclinical mastitis treatment after intramammary infusion of an antimicrobial active ingredient at drying time in two different formulations, conventional and nanoparticulate, to verify spontaneous cure rates, to evaluate the ability to prevent new mammary infections, and to verify the presence of antimicrobial residues in the milk of sheep subjected to treatment at drying off in consecutive lactations. The study was conducted on a flock located on a farm in the municipality of São Carlos, São Paulo, Brazil. The use of cloxacillin at the time of drying off beef sheep in the flock with subclinical mastitis observed in this study is an effective method for reducing these infections after calving when administered in a nanoencapsulated structure.