Fuente: WIPO "meat" There is provided an assay to determine whether an animal has an allele for or exhibits muscle fibre composition characteristic of a Duroc pig. The assay comprises obtaining a tissue sample from said animal and subjecting said sample to genetic analysis and/or obtaining a muscle sample from said animal and determining by histochemical or immunochemical analysis whether said sample exhibits phenotypic traits indicative of said allele(s) and/or shows a muscle composition characterisitc to the Duroc pig. Suitable physical traits include the following: i. the percentage frequency of SO fibres present in said muscle; and/or ii. the number of SO fibres present per cluster; and/or iii. the number of muscle fibres present per cluster; and/or iv. the level of m calpain present per unit muscle; and/or v. the level of $g(m) calpain present per unit muscle. The assay can be used to select animals having Duroc muscle type for breeding or for meat production. Anti-calpain antibodies are especially useful and may be employed as part of an ELISA style assay.