Relationship of plasma leptin concentration to intramuscular fat content in beef from crossbred Wagyu cattle

Plasma leptin concentrations and beef cattle carcass characteristics in eight Continental Crossbred steers [0% Wagyu Cattle (WC)] were compared to crossbred cattle with 50 and 75% WC (eight steers each) genetic makeup to determine if a relationship exists between plasma leptin concentrations and intramuscular fat content (marbling) in beef cattle. Plasma leptin concentrations were measured at two stages of cattle growth, 16 and 4 wk prior to slaughter (W P S). Beef cattle characteristics including marbling score, ribeye area, i.m. total lipid content, and backfat depth were determined, and correlation coefficients obtained between these traits and leptin concentration at both sampling dates. Plasma leptin concentrations increased relative to the lipid content in the 24 steers based on the significant positive correlation observed between plasma leptin and total lipids (% wet weight) from both pars costalis diaphragmatis (p.c.d.)(16 WPS: r = 0.69, P = 0.0004; 4 WPS: r = 0.35, P = 0.104) and longissimus (16 WPS: r = 0.59, P = 0.002; 4 WPS: r = 0.51, P = 0.011) muscles. A trend was observed, however, at 4 WPS when the groups of varying Wagyu genetics were compared. Plasma leptin was positively correlated with muscle lipid content for the 0% Wagyu cattle (longissimus: r = 0.62, P = 0.103; p.c.d.:r = 0.40, P = 0.410)but there was almost no correlation in these parameters for the 50% WC (longissimus: r = 0.11, P = 0.797; p.c.d.: r = 0.005, P = 0.990). Plasma leptin concentration was negatively correlated with lipid content in the 75% WC (longissimus: r = –0.60, P = 0.120; p.c.d.: r = –0.65, P = 0.164). The results suggest that increasing Wagyu genetics negates any relationship between leptin concentrations and i.m. fat content in cattle. Key words: Wagyu crossbred cattle, meat quality, intramuscular fat, marbling, leptin