Regulatory controls to prevent the spread of BSE have prohibited the use of certain animal proteins in feed in several countries. Accurate analytical methods for detecting prohibited material in feedstuffs are needed to ensure compliance with the new regulations. Six IgG class monoclonal antibodies (MAbs) against troponin I (TnI), a thermostable marker protein, have been developed for the detection and differentiation of rendered muscle tissue in animal feed. MAbs 1F9, 2G3 and 7F7 reacted to TnI of all species, including mammalian, poultry and fish, while MAbs 7A12 and 8A12 recognized only mammalian TnI (porcine, bovine, ovine, equine, and deer). MAb 2A8 was able to differentiate TnI of ruminant origin (bovine, ovine and deer) from other species. Three indirect enzyme-linked immunosorbent assays (ELISAs) employing these MAbs were developed for the determination of animal muscle, mammalian muscle or ruminant muscle in animal feeds.