Associations of Leptin Gene Marker with Carcass Traits in Cattle

Objectives of this study were to determine the effects of leptin (ob) genotype on fat and muscle traits in crossbred cattle. A single nucleotide polymorphism located in exon 2 of the ob gene in cattle codes for an amino acid change from an arginine (R) to a cysteine (C). Genotypes for leptin were determined on crossbred calves (n = 492) by Acil digestion of amplified PCR product (C allele: 130bp; R allele: 73bp and 57bp ). The genotypic frequencies of CC, CR, and RR were .240, .561, and .199, respectively within the calves. Data were analyzed by least-squares, accounting for discrete effects of genotype, sex, year, location, and breed-type. Three analyses were performed, adjusting for covariates of carcass weight, fat thickness, or age at slaughter. Data were also analyzed using a continuous model, with trait values regressed on the number of \u27C\u27 alleles present in the genotype. Subjective marbling scores (assigned by USDA grader; 350 = slight 50, 400 = small 0, 450 = small 50) were significantly higher (P = .06) for CC (411 units) than for RR (3 87 units) genotype when· adjusted to a constant slaughter age (433 days). Similar, more significant (P\u3c.05) differences between genotypes in marbling scores were observed when adjusting to a constant carcass weight (328 kg) or external fat thickness ( 11.5 mm). The effect of genotype on external fat thickness approached significance when analyzed on a weight-constant basis (12.7 and 12.1 mm for CC and RR, respectively; P = .07). Effects of regressing trait values on genotype suggested mainly additive effects on fat related traits. However, %KPH exhibited dominance in all three analyses. The effect of genotype was nonsignificant for carcass weight and longissimus muscle area. In conclusion, leptin genotypic effects were significant, though modest in magnitude, for traits related to intra-muscular and subcutaneous fat accretion