Results
Leptin Receptor
Daily gain and backfat thickness are important traits for livestock producers to consider in order to produce efficient, fast growing and lean animals. The leptin receptor gene (LEPR), is a high affinity receptor (for review see Tartaglia, 1997) that mediates the regulation of the well known "obesity" gene, leptin (Zhang et al., 1997). Mutations in LEPR have been reported to be associated with obesity in humans and rodents (Reichart et al., 2000; Clement et al., 1998; Chen et al., 1996). Given the physiological role of LEPR, it is interesting as a candidate gene for backfat deposition and daily gain in the pig. Vincent et al. (1997) identified a HinfI polymorphism in porcine LEPR and mapped its location to pig chromosome 6 (SSC6). A few studies have reported on associations between leptin levels and production traits in pigs (Ramsay et al., 1998; Robert et al., 1998), but the effects of LEPR on pork quality traits of economic importance to the industry have not been investigated.
A LEPR MboI PCR-RFLP, developed by Vincent at Iowa State University Rothschild, (personal communication), was found to be polymorphic in all breeds analyzed. Allele 2 was the most frequent (0.91) in the total population and was found to be associated with leaner animals (Table 1).
Total population analysis revealed effects (P< 0.05) of LEPR on last lumbar backfat with the 11-animals having the fattest phenotype (Table 1). Although not significant (P>0.05), last rib and 10th rib backfat (not shown) had similar numerical trends. Average daily gain was also different (P< 0.05) between the genotypes (Table 1). The results of the individual breed analyses (not shown) revealed differences (P< 0.05) between LEPR genotypes and off flavor score for Berkshire; average daily gain and Japanese color score for Duroc; glycolytic potential, loin glycogen and lactate concentration, intramuscular fat, and quality index (which includes Minolta, IMF, & pHu) for Hampshire; 10th rib backfat, average daily gain, loin pHu, Minolta and Hunter color values, and quality index for Landrace.
As previously reported in other mammalian species, LEPR appears to have the greatest effects on backfat and average daily gain in the pig, but may also be associated with correlated pork quality differences within genetic lines.