The present invention relates to the identification of a single nucleotide polymorphism (SNP) within the bovine CAST locus encoding the calpastatin protein, wherein the allelic variation of the SNP is a G/C transversion associated with post-mortem muscle tenderness. The invention further relates to oligonucleotides useful in identifying the genotype of bovines as it relates to the CAST locus polymorphic site. The invention also encompasses computer-assisted methods and systems for improving the production efficiency for livestock having marketably tender meat using multiple data, and in particular the genotype of the animals as it relates to the CAST SNP. These methods of the invention encompass obtaining a genetic sample from each animal in a herd of livestock, determining the genotype of each animal with respect to specific quality traits as defined by a panel of at least two single polynucleotide polymorphisms (SNPs), one SNP corresponding to a site between exons 5 and 6 of the bovine CAST locus, grouping animals with like genotypes, and optionally, further sub-grouping animals based on like phenotypes.