An undesired consequence of the use of antimicrobial drugs in cattle is the presence of drug residues in the milk of lactating animals. In lactating dairy cattle, this translates into production losses due to withholding of nonsaleable waste milk containing drug residues. To avoid discarding this valuable product while reducing feed costs, many dairies feed waste milk to preweaned calves.
Regardless of the financial advantages of feeding waste milk to calves, an important question is whether this practice can affect the calves’ health and result in unnecessary selection of antibiotic resistant bacteria that could reduce successful outcomes when treating infections with antibiotics.
Cephapirin is a drug that can be found in drugs used commercially for treatment of cows with mastitis . Mastitis treatment is the most common use of antibiotics on dairy farms; therefore it is not surprising that most drug residues in waste milk are probably a consequence of treating cows with mastitis. This finding highlights even further the importance of management efforts to reduce the cases of mastitis in the herd,