IntroductionIn Austria, veterinary medicinal products (VMPs) containing penicillin G or cefoperazone are frequently used to treat dairy cows, which leads to the production of non-saleable waste milk. This study aimed to determine the loss of detectable antimicrobial activity of penicillin G and cefoperazone using a commercial ß-lactamase preparation, Antipen®.MethodsUltra-high-temperature (UHT) processed and raw unpasteurized milk were spiked with penicillin G and cefoperazone (both pure pharmac