RESUMO
A SNP in the promoter region of insulin like growth factor-1 (IGF1) (c.-512C>T) was analysed for associations with 10 fat deposition and carcass merit traits in hybrid (n = 455), Angus (n = 204) and Charolais (n = 186) beef cattle populations. Significant associations of the SNP were found for ultrasound backfat thickness (P = 0.030), carcass average backfat (P = 0.015) and carcass lean meat yield (LMY) (P = 0.023) in the Angus beef population, with the 'CC' genotype showing higher fat depth and lower LMY than the 'TT' genotype. Analyses of transcription factor binding sites based on transcription element search system prediction revealed that the 'C' allele introduces a binding site for nuclear factor I, which has an adipose tissue-specific regulatory role and thus may contribute to the SNP effect on fat deposition in the population of pure Angus cattle, a breed with greater fat depth than the hybrid and Charolais breeds.
Assuntos
Tecido Adiposo/anatomia & histologia , Composição Corporal/genética , Fator de Crescimento Insulin-Like I/genética , Animais , Pesos e Medidas Corporais/veterinária , Cruzamento , Bovinos , Primers do DNA/genética , Estudos de Associação Genética/veterinária , Modelos Lineares , Polimorfismo de Nucleotídeo Único/genética , Especificidade da Espécie , Fatores de Transcrição/metabolismoRESUMO
Longissimus muscle area and fat thickness were measured following weaning, at yearling, and prior to harvest using real-time ultrasound, and corresponding carcass measurements were recorded 3 to 7 d following the preharvest scan in composite steers (n = 116, 447 +/- 19 d), bulls (n = 224, 521 +/- 11 d), and heifers (n = 257,532 +/- 12 d). Although fat deposition was limited in bulls and heifers from weaning to yearling, coefficients of variation ranged from 8.46 to 13.46% for muscle area, and from 27.55 to 38.95% for fat thickness, indicating that significant phenotypic variance exists across genders. Residual correlations, adjusted for the effects of year of birth, gender, and age at measurement, were high and ranged from 0.79 to 0.87 among ultrasound and carcass measures of muscle area. Residual correlations among ultrasound and carcass measures of fat thickness were also high, ranging from 0.64 to 0.86. Weaning and/or yearling ultrasound muscle area yielded similarly accurate predictions of carcass muscle area. Yearling ultrasound fat thickness accounted for 13% more of the observed variance in carcass fat thickness than the weaning ultrasound measure in single-trait prediction models. When both weaning and yearling ultrasound measures were used to predict carcass fat thickness, partial R2 values were 0.15 and 0.61 for weaning and yearling ultrasound fat thickness, respectively. The difference between predicted and carcass measures with respect to muscle area (fat thickness) was less than 6.45 cm2 (2.5 mm) for 80.2 to 88.9% (90.3 to 95%) of animals. Preharvest ultrasound measures yielded standard errors of prediction of less than 4.95 cm2 for muscle area and 1.51 mm or less for fat thickness. These results indicate that ultrasound measures taken between weaning and yearling provide accurate predictors of corresponding carcass traits in steers, bulls, and heifers.