Evaluation of antibiotic residues in commercial milk of Pirassununga city, southeast region og Brazil. 1. Beta-lactam occurence - Rosario, Tatiana Reis do; Fonseca, Luis Fernando Laranja da; Rodrigues, Paulo Henrique Mazza (Congresso Panamericano de Qualidade do Leite e Controle de Mastite = Panamerican Congress on Milk Quality and Mastits Control, 2002)