Melanocortin-4 receptor (MC4R) gene is part of the central melanocortin pathway located in the hypothalamus, an area of the brain in which appetite is regulated. Insulin-like growth factor 2 (IGF2) gene plays a role in muscle growth, myoblast proliferation and differentiation. Thus, they are candidate genes for feed conversion efficiency (FCE). The study was to investigate the effects of variants in cattle MC4R and IGF2 gene on FCE traits including residual feed intake (RFI), feed conversion ratio (FCR) and average daily gain (ADG). We screened single nucleotide polymorphisms (SNPs) of the two genes in 118 Simmental bulls by DNA-pool sequencing and genotyped by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analysis. C1069G locus of MC4R and four SNPs (C2209T, G18587C, A22950T and G26920T) of IGF2 were identified in the population. The χ2 test showed that only MC4R-C1069G, IGF2-C2209T and IGF2-G18587C loci fitted with Hardy-Weinberg equilibrium (P>0.05). General linear model (GLM) was used to analyze differences between genotypes. The results showed that only IGF2-G18587C locus has a significant effect on ADG (P<0.05), but has no significant effect on RFI or FCR (P>0.05). CC and GG genotypes were the dominant genotypes; individual with CC or GG genotype had a larger ADG than GC (P<0.05).

Key words: Beef cattle, Feed conversion efficiency, IGF2, MALDI-TOF-MS, MC4R