Antimicrobial Residues and Resistance: Understanding and Managing Drug Usage on Dairy Farms

Introduction In modern dairy cattle operations, antimicrobials are administered for both therapeutic and prophylactic purposes. Most antimicrobials are used therapeutically but some antimicrobials are used to prevent disease in healthy animals during periods of increased susceptibility. Mastitis is one of the most frequent infectious diseases in dairy cattle and accounts for most of the doses of antibiotics given to dairy cows (Pol and Ruegg, 2006a). Lactating cows may be treated for clinical mastitis or to pursue bacteriological cure of a subclinical case. Antimicrobials are also used to treat other infectious diseases of dairy cows, including respiratory and uterine infections and infectious foot disease.