The FDA found it expedient to subdivide this term into two categories, according to the withdrawal period necessary to be observed prior to slaughter for animals about to enter the human food chain; and Prior to the enactment, only two categories of animal feed drugs existed: over-the-counter or prescription.
[1][2][3] New animal drugs are the functional ingredients for medicated feeds.
It contains a substantial quantity of nutrients including vitamins, minerals, and/or other nutritional ingredients...
On 1 January 2017, veterinary oversight was added to a significant number of antibiotic drugs in animal feed, so as to ensure that they are "medically necessary".
The VFD label was applied to, among others, chlortetracycline, hygromycin, penicillin, lincomycin, oxytetracycline, tylosin, virginiamycin and neomycin.