Animal Drug and Animal Generic Drug User Fee Amendments of 2023 This bill reauthorizes the Food and Drug Administration (FDA) to collect fees for brand-name and generic animal drug applications through FY2028. It also makes related updates to fee calculations and FDA reporting requirements. The bill also (1) provides for a specific fee for requests to establish generic investigational new animal drug files and requires other application fees to be adjusted accordingly; (2) authorizes the FDA to remove species from the definition of major species (currently horses, dogs, cats, cattle, pigs, chickens, and turkeys); (3) provides statutory authority for the FDA to report on its progress supporting antimicrobial stewardship in veterinary settings (i.e., supporting responsible use of antimicrobial drugs for animals to slow the development of drug-resistant bacteria); and (4) provides for the regulation of zootechnical animal food substances as food additives (zootechnical animal food substances are added to the food or drinking water of animals to affect the byproducts of the animal's digestion, reduce foodborne pathogens, or alter the animal's gastrointestinal biome). Animal drugs are drugs that are intended for animals other than humans (e.g., pets and livestock). Animal drugs must be approved by the FDA before they may be offered on the commercial market. The FDA is authorized to collect fees for animal drug applications in order to support its regulatory activities; this authority currently expires at the end of FY2023.