Livestock animals may get exposed to an agrochemical through intake of residue-containing diet or via contact from applications made to their surroundings. Metabolism studies in livestock animals are carried out to define the terminal residue and develop residue definition for risk assessment and tolerance enforcement in edible commodities of meat, milk, and eggs. The metabolism studies are conducted with 14C-labeled agrochemical to facilitate quantification of residue in tissue and commodity samples, identification of metabolites, and tracing of the metabolic pathways. The test animals are selected from ruminants (lactating goat or cow) and poultry (laying hens). The animals are orally dosed with the agrochemical in the diet for a set duration. The samples are collected at the appropriate stages during the experiment and after the sacrifice. Tissue and commodity samples containing significant residue are extracted and analyzed. Based on the identities of the metabolites, a metabolic pathway in the test animal is proposed. The metabolites with probable toxicological concern are included in the residue definition for risk assessment and tolerance enforcement in edible commodities. The chapter also describes the conduct of an animal metabolism study and discusses the metabolic pathways of selected agrochemicals in livestock animals.