Effects of dietary copper source and level on metabolic hormones and lipogenic and lipolytic enzyme activities in lambs

This experiment was conducted to determine the effect of dietary copper (Cu) on metabolic hormones and activities of lipogenic and lipolytic enzymes in lambs. Fifty Dorper×Mongolia wether lambs (approximately 3 month of age; average BW= 23.8±0.6 kg) were randomly assigned to one of five treatments. Treatments consisted of (1) control (no supplemental Cu), (2) 10mgCu/kgDM from Cu-lysine, (3) 20mgCu/kgDM from Culysine, (4) 10mgCu/kgDM from tribasic copper chloride (Cu2(OH)3Cl; TBCC), and (5) 20mgCu/kgDM from TBCC. The Cu concentration was 6.74 mg/kg DM in the basal diet. Blood samples were collected on days 0, 30, and 60, and then the lambs were slaughtered on day 60. Plasma insulin concentration was decreased (P < 0.05) by Cu supplementation on days 30 and 60. Plasma leptin concentration was not affected on day 30, but was increased (P < 0.05) on day 60 in lambs supplemented with Cu compared with the controls. The activities of fatty acid synthase (FAS), NADP-malate dehydrogenase (MD), and glucose-6- phosphate dehydrogenase (G6PDH) were decreased (P < 0.05) in subcutaneous (SC) adipose and liver tissues by Cu supplementation. Lipoprotein lipase (LPL) activity was decreased by Cu supplementation (P < 0.05) in SC adipose tissue, but was not affected (P > 0.05) in liver tissue. Hormone-sensitive lipase (HSL) activity was increased (P < 0.05) in SC adipose and liver tissues by Cu supplementation. There were no differences between supplemental Cu form or level in metabolic hormone levels or activities of FAS, MD, G6PDH, LPL, or HSL. These results indicate that Cu supplementation altered plasma insulin and leptin metabolism, decreased lipogenic enzyme activities, and increased lipolytic enzyme activities in SC adipose and liver tissues in lambs. The reduction in backfat depth of lambs may be due to effects of Cu in reducing synthesis of adipose tissue and increasing lipolysis.