There are genetic differences in the hepatic glucose and linoleic acid metabolisms between Muscovy and Pekin ducks ad libitum-fed. To understand the effect of overfeeding on the hepatic metabolisms in these two species of ducks, we compared the different pathways of glucose and linoleic acid reaching the liver of Muscovy (Cairina moschata) (n=6) and Pekin (Anas platyrhynchos) (n=6) ducks overfed for 1 week and sacrificed 2-4 h after their last meal by using the ex vivo method of liver slices incubated for 16 h with [U-(14)C]-glucose, [1-(14)C]-linoleic acid and [(35)S]-methionine added to the survival medium. The glucose was the main precursor of triacylglycerol synthesis in the liver of these two species and its hepatic metabolism was similar between species. The hepatic uptake of linoleic acid was 1.7-fold higher (P=0.020) in the Muscovy duck than in the Pekin duck leading to a 1.9-fold higher (P=0.017) esterification of this fatty acid in the liver of the Muscovy duck than in that of the Pekin duck. Finally, both species after I week of overfeeding exhibited the same capacity to secrete VLDL remaining insufficient to avoid hepatic steatosis. (C) 2008 Elsevier Inc. All rights reserved.