ECFR 501 principal display panel

21 CFR 501 establishes FDA's labeling rules for animal food (including pet food) under the Federal Food, Drug, and Cosmetic Act. Its sections include: 501.1 (principal display panel of package-form animal food), 501.2 (information panel), 501.3 (identity labeling), 501.4 (designation of ingredients), 501.5 (name and place of business of manufacturer, packer or distributor), 501.8 (number of servings), 501.15 (prominence of required statements), 501.17 (warning statements), 501.18 (misbranding of animal food), 501.22 (labeling of spices, flavorings, colorings and chemical preservatives), 501.100 (exemptions), 501.103 (exemption petitions), 501.105 (declaration of net quantity of contents when exempt) and 501.110 (collective names for feed ingredients). Note: the well-known 95% / 25% / 3% / flavor naming rules are NOT part of 21 CFR 501 — they come from AAFCO Model Regulation PF3, which most US states adopt: the 95% rule (named ingredient ≥95% of total weight excluding processing water, ≥70% including it), the 25% "dinner/formula/recipe" descriptor rule, the 3% "with" rule, and flavor designations requiring only an identifiable flavor source. Labels that are false or misleading render the product misbranded (21 CFR 501.18; FDCA misbranding provisions, 21 U.S.C. 343).