The objective of this study was (i) to analyze antibiotic residues, two which were beta-lactam antibiotics, one tetracycline, and one quinolone in the milk of lactating animals; (ii) to evaluate the interference of the drug ceftiofur which is considered as discard-zero. The SNAPduo™ ST Plus kit was used to evaluate the presence of beta-lactam antibiotics and tetracyclines in natural milk. Medications based on penicillin, ceftiofur, enrofloxacin, and oxytetracycline were used. As expected, the milk from control animals and animals administered with enrofloxacin did not present antibiotic residue because it is not one of the classes detected by the SNAPduo™ ST Plus kit, and thus it was used to prove the efficiency of the test. Ceftiofur, known as a “discard-zero” antibiotic, tested positive for the SNAPduo™ ST Plus kit and the BetaStar Combo® “S” test. Chemical residues were detected in cow’s milk treated with different groups of antibiotics after the withdrawal time indicated in the package inserts of the medicines used.