Hops (Humulus lupulus L.) are a phytochemical resource rich in bitter acids, prenylated flavonoids, and essential oils with antimicrobial, antifungal, antioxidant, and anti-inflammatory activities relevant to animal production. This review critically synthesizes the phytochemical profile of H. lupulus and the available in vivo evidence on its use as a functional feed additive in poultry, freshwater aquaculture, swine, and ruminants, identifying research gaps and regulatory barriers. In poultry, microencapsulated β-acids at 30 mg/kg feed achieved a feed conversion ratio comparable to zinc bacitracin, while lupulone reduced intestinal Clostridium perfringens counts by >4 log units, from log₁₀ 6.20 to 2.00 CFU/g; doses ≥240 mg/kg induced adverse effects. In freshwater aquaculture, hop extract at 750 mg/kg feed improved hepatic markers and fillet fatty acid composition in common carp, whereas isolated hop acids at 308 mg/kg increased final body weight in Nile tilapia (157.3 vs. 150.3 g) without sensory rejection even at 1230 mg/kg. In swine, granulated cones improved feed conversion (3.5 vs. 4.3 kg/kg), while purified β-acids up to 360 mg/kg improved performance comparably to colistin. In ruminants, hop residues, pellets, and cones were tolerated without consistent production benefits. Overall, hop-derived additives show dose-, compound-, and matrix-dependent effects, requiring standardized formulations, species-specific pharmacokinetics, pathogen-challenge validation, long-term safety assessment, and regulatory dossiers.