| The objective was to characterize variation in molecular markers associated with carcass traits in three crossbred families of beef cattle. Three half-sib families were developed from crossbred sires to make up the reference population of 238 animals. The genetic background of the sires, dams, and offspring was 1/3 Angus, 1/3 Hereford, 1/3 Simmental. Animals were housed at the South Dakota State University Beef Breeding Unit, Brookings, SD. Calves were born between 2001 and 2004. Carcass traits collected were finished weight, hot carcass weight, marbling score, Quality Grade, longissimus muscle area, back fat, percent kidney, pelvic, and heart fat, and Yield Grade. Two studies were conducted to assess the association of markers with economically important traits. In the first study, polymorphisms of the leptin gene were evaluated. Effects for marbling score with genotype for a marker developed on leptin exon 3 were detected in family 2 (p<0.05). In the same family, the ability to grade Choice was associated with genotype for a marker on leptin exon 2 (p<0.05), exon 3 (p<0.001), and promoter (p<0.01). Family 2 also displayed an association for sire allele and ability to grade Choice (p<0.01) with the marker on leptin exon 3 and promoter. Family 3 showed an association between genotype and marbling score with the marker on leptin exon 2 (p<0.05). Family 1 had a significant association between the leptin promoter GA deletion marker with Yield Grade (p<0.05). Leptin haplotype was associated with ability to grade Choice in family 2 (p<0.01). In the second study of microsatellite markers on bovine chromosomes 5 and 6 were used to assess their associations with carcass traits. On chromosome 5, markers RM103 and BM321 were associated with finished (P<0.01) and carcass (P<0.05) weights in family 1. An association with marbling score was identified on chromosome 5 with BM6026 (P<0.05), RM103 (P<0.01), and BM321 (P<0.01) in family 1. On chromosome 6, BMC4203 was associated with longissimus muscle area in family 1 (P<0.05) and family 2 (P<0.001). No association was detected (P>0.05) on family 3. |
