Two batches of male mule ducks were constituted on the basis of the filling state of the crop at slaughter, after being over-fed twice a day for 5 days: no corn in the crop defined 'OV' birds, and corn in the crop defined 'OP' birds. 'OP' animals presented significantly lower daily consumption during the last 3 days of force-feeding. They had a lighter liver weight than 'OV' ducks (178 versus 197 g), lower hepatic lipid percentages (25.0 versus 33.0%), and enhanced hepatic glycogen rates (4.7 versus 2.4%). Metabolic state of animals might explain these variations in hepatic composition. Unadaptation to force-feeding modifies the metabolic inbalance of the overfed animals and consequently induces higher levels of carbohydrate. These results suggest that similar differences between crude fatty livers could be reflected in the quality of the cooked products.