Effects of dietary protein level during rearing period and age at overfeeding on magret and foie gras quality in male mule ducks.

The aim of this trial was to study the effects of dietary protein content during the rearing period on the performance of mule ducks, according to age at overfeeding (O). Ducks (n = 612) were divided into four groups differing in the protein content in the diet offered during the starting period (S, 0-20 days; Sl vs. Sh : 150 vs. 175 g/kg crude protein (CP)) and growing-finishing period (GF; 21-67 or 81 days, depending on age at O; GFl vs. GFh : 133 vs. 152 g/kg CP). The relative weight of pectoral muscle was lower when ducks were fed a low protein diet during S (-5%, P < 0.01) or GF period (-6%, P < 0.001) at 68 days and higher in ducks of the Sl GFh group (+6%; P < 0.05) at 82 days. Both foie gras and magret weights fell when ducks were fed Sl or GFl (P < 0.05 and < 0.01). Mortality during the O period was higher in ducks fed the Sl diet and overfed at late age (7.4% vs. 0%; P < 0.01). In conclusion, a reduction in the dietary protein supply should be recommended only during the GF period for ducks overfed at a late age.