Quantitative trait loci affecting growth and carcass composition of cattlesegregating alternate forms of myostatin

The effects of the bovine myostatin gene on chromosome 2 on birth and carca ss traits have been previously assessed. The objective of this study was to identify additional quantitative trait loci (QTL) for economically importa nt traits in two families segregating an inactive copy of myostatin. Two ha lf-sib families mere developed from Belgian Blue x MARC III (n = 246) and P iedmontese x Angus (n = 209) sires. Traits analyzed were birth (kg) and yea rling weight (kg); hot carcass weight (kg); fat depth (cm); marbling score; longissimus muscle area (cm(2)); estimated kidney, pelvic, and heart fat ( %); USDA yield grade; retail product yield (%); fat yield (%); and wholesal e rib-fat yield (%). Meat tenderness was measured as Warner-Bratzler shear force at 3 and 14 d postmortem. The effect of myostatin on these traits was removed by using phase information obtained from the previous study with s ix microsatellite markers flanking the locus. Selective genotyping was done on 92 animals from both families to identify genomic regions potentially a ssociated with retail product yield and fat depth, using a total of 150 inf ormative markers in each family. Regions in which selective genotyping indi cated the presence of QTL were evaluated further by genotyping the entire p opulation and additional markers. For the family with Belgian Blue inherita nce (n = 246), a significant QTL for birth and yearling weight was identifi ed on chromosome 6, Suggestive QTL were identified for longissimus muscle a rea and hot carcass weight on chromosome 6 and for marbling on chromosomes 17 and 27. For the family with Piedmontese inheritance (n = 209), suggestiv e QTL on chromosome 5 were identified for fat depth, retail product yield, and USDA yield grade and on chromosome 29 for Warner-Bratzler shear force a t 3 and 14 d postmortem. Interactions suggesting the presence of QTL were o bserved between myostatin and chromosome 5 for Warner-Bratzler shear force at 14 d postmortem and between myostatin and chromosome 14 for fat depth. T hus, in families segregating an inactive copy of myostatin in cattle, other loci influencing quantitative traits can be detected. These results are th e initial effort to identify and characterize QTL affecting carcass and gro wth traits in families segregating myostatin.