Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 9, 1997
Publication Date: N/A
Interpretive Summary: The inheritance pattern of alternate forms, alleles, of a gene on bovine chromosome 2 determines the double muscled appearance. Inheritance of two copies of the double muscle allele results in visible increase in muscling, especially in the hindquarter. Animals inheriting one copy of this allele and one copy of the normal allele cannot be visibly distinguished from those inheriting two copies of the normal allele. Previous studies deter- mining the effect of a one copy of the double muscling allele on carcass characteristics were complicated by breed-effect or subjective evaluations. We have used DNA markers to tract the presence or absence of the double muscling allele in a genetically heterogeneous population of cattle. Individuals with a single copy of this allele had a 6.5% increase in ribeye area. Also, these individuals had 13% less fat trim. These carcass traits along with several others led us to conclude that one copy of the double muscling allele results in a leaner more muscular carcass. DNA markers in combination with mating schemes to maximize the production of offspring with one copy of the double muscling allele is a viable approach to producing leaner cattle.
Technical Abstract: A locus near the centromere of bovine chromosome 2 (BTA2) is responsible for muscle hypertrophy (mh) in cattle. The objectives of this study were to refine the genomic region in which the locus resides and to assess the effects of a single copy of the mh allele on carcass and birth traits. Two half-sib families were developed using a Belgian Blue x MARC III (n=246) or ra Piedmontese x Angus (n=209) sire. Six microsatellite markers were used to determine the presence or absence of the mh allele and to confirm that the locus affecting the traits was in the proximal region of BTA2. Calving ease (CE) and birth weight (BWT, kg) were analyzed. Carcass traits evaluated were longissimus rib eye area (REA, cm2), retail product yield (RPYD, %), USDA yield grade (YG), marbling (MAR), fat thickness (FAT, cm), estimated kidney, pelvic, and heart fat (KPH, %), and longissimus tenderness measured as Warner-Bratzler shear force at 3 (S3) and 14 (S14) d dpostmortem. The location of mh was assessed to be 4 cM from the beginning of the linkage group, with the 95% confidence interval between 2 and 6 cM. Cattle with an mh allele had increased (P<0.01) REA, RPYD, and BWT, and decreased MAR, YG, FAT, and KPH, compared to those without the allele. The effects of the mh allele (mh/+ vs +/+) were 1.35, 1.6, .41, -1.01, -1.42, -.84, and -.86 residual standard deviations, respectively. There were no effects (P>.10) for CE, S3, and S14. Allelic differences due to the mh locus were similar for both sources (Belgian Blue or Piedmontese). Individuals inheriting a single mh allele had a leaner, more heavily muscled carcass compared to those inheriting the alternative allele. Thus, mating schemes that maximize production of mh/+ genotypes provide a viable approach for improving carcass composition.