The relation between plasma leptin concentrations and carcass lipid contents in Japanese Black steers

We investigated a relation between carcass lipid contents and plasma leptin in 40 Japanese Black steers, which were fed a 12% crude protein diet (CP12) or a 16% crude protein diet (CP16) in the growing phase (from 10 to 18 months of age) and a low starch level diet (LS) or a high starch level diet (HS) in the finishing phase (from 19 to 27 months of age). Plasma leptin concentrations were measured by multi-species leptin radioimmunoassay kit using recombinant bovine leptin as the standard. The CP16 group had greater backfat thickness at slaughter compared with the CP12 group (P < 0.01). The HS group showed greater weight gain (P < 0.05) and yielded larger area of longissimus muscle (P < 0.01) than the LS group. Plasma leptin was significantly increased (P < 0.01) with age; however, leptin levels had no relation to feed intake. Backfat thickness at slaughter was positively associated with the rate of the increase in plasma leptin concentrations from 11 to 14 months of age, especially in the CP16 group (r = 0.59, P < 0.05). However, plasma leptin levels seem to be weak index to predict final adiposity in Japanese Black steers. (C) 2001 Elsevier Science B.V. All rights reserved.