Results
Melanocortin-4 Receptor
Melanocortin-4 receptor (MC4R) has been found to play a significant role in regulating leptin's effects on food intake and body weight (Seeley et al., 1997; Fan et al., 1997). Kim et al. (2000) demonstrated that a missense mutation in MC4R was associated with backfat thickness, growth, and feed intake in different genetic lines of pigs. No studies to date have reported associations between meat quality characteristics and MC4R genotypes.
Results with the TaqI MC4R PCR-RFLP (PIC/Iowa State patent pending), developed by Kim et al. (2000), show an allelic frequency of 0.60 for allele 2, which was associated with much fatter animals in the total population. Genotypic frequencies varied within the breeds, however the heterozygote 12-animals were the most frequent (0.45) in the total population.
The effect of MC4R on last lumbar backfat was highly significant (P<0.001) (Table 1). Approximately, 0.18 cm in last lumbar backfat is added with the inclusion of each 2 allele. The MC4R genotype groups were also different (P <0.05) for last rib backfat and 10th rib backfat approached significance (P=0.085) with the fatter 22-animals being in line with the last lumbar result. These backfat results are also in agreement with Kim et al. (2000) who demonstrated that 11-homozygote pigs had approximately 9 % less backfat than 22-pigs. Instron force was less (P<0.05) for the 22-genotype (Table 1), indicating increased tenderness in the fatter animals. Interesting trends in loin muscle area, average daily gain, and color score were also noted. The results of the individual breed analysis (not shown) revealed differences (P<0.05) between MC4R genotypes and soundness score, last lumbar backfat, last rib backfat, average backfat, average daily gain, and loin lactate concentration for Berkshire; and juiciness score, intramuscular fat, Minolta, Hunter color, and quality index for Landrace.
Our results suggest that MC4R has its greatest effects on backfat and Instron tenderness for the total population. However, differences between MC4R genotypes were also reported for average daily gain and meat quality traits within the breed populations. Further analysis in larger populations will be needed with this marker to fully characterize the effects of MC4R on meat quality.