Effect of one copy of the nt821 mutation in the myostatin gene on yearling traits in Senepol cattle.

Several mutations in the myostatin gene cause double muscling in beef cattle. Studies indicate a significant effect of these mutations on traits used as selection criteria. One mutation that occurs in Senepol cattle is known as nt821. This mutation is important to understand the effects of double muscling in this breed. Records from 5,235 purebred Senepol cattle undergoing commercial performance tests in Brazil were used. Phenotypes and expected progeny differences for yearling weight (YW), scrotal circumference (SC), carcass conformation score (CCS), ribeye area (REA), backfat thickness (BF), intramuscular fat (IMF), and residual feed intake (RFI) were assessed. In the population studied, 861 animals were heterozygotes and 4,374 animals were wild-type homozygotes. There were no nt821 homozygotes. One copy of the nt821 mutation caused losses (P < 0.01) in SC, BF, and IMF. On the other hand, the nt821 mutation provided better results for REA (P < 0.01). There were no differences (P > 0.01) in YW, CCS or RFI between genotypes. Heterozygous animals exhibited greater muscle deposition but less subcutaneous and intramuscular fat deposition in the carcass, in addition to losses in indicators of precocity, when compared to animals carrying no copy of the mutation.