At the end of the recommended milk discard time and after the milk becomes visually normal, test milk from any lactating cow treated for mastitis. Also, test problem cows that have been treated longer than recommended, or with higher doses, or with combinations of drugs or special mixes. All new additions to the herd including purchased cows or first lactation animals should be tested before their milk is added to the bulk tank. Any cull cows that have been treated or baby calves that have been fed milk from treated cows should not be sold until the end of the withdrawal time for meat animals. Calves born to cows treated during the dry period may acquire tissue drug residues prior to birth or from drinking colostrum.
Tests are available for use on urine or serum samples for certain drugs.
Certain factors increase the reliability of using antibiotic residue screening tests. Choose a screening test that is appropriate for detecting the antibiotic administered. Do not treat cows who have little chance to respond, e.g., for example, cows chronically infected with Staphylococcus aureus . Test milk that is visually normal. Test composite milk rather than foremilk.