Feed efficiency in the laying duck: appropriate measurements and genetic parameters.

The objective of this study was to characterize residual feed intake (RFI) in common laying ducks by a) adjusting position and duration of the measurement period and b) estimating genetic parameters of RFI. The feed intake (FI), BW, and egg mass laid (EML) were recorded for 64 I444 common ducks at the beginning (-35 wk of age) and the middle (41-48 wk of age) of the laying curve. Much feed wastage was observed at the beginning of the laying curve and led to biased FI data. However, when laying was well-established, weekly and fortnightly FI measurements were well correlated phenotypically (Rp from 0.84 to 0.92 and from 0.91 to 0.94, respectively for weekly and fortnightly FI) with the measurements over the whole 2-mo period. Regarding egg mass laid, phenotypic correlations between the one-week measurements and the measurements over the whole 2-mo period were more variable than those for FI, ranging from 0.74 to 0.94, and similar to whatever was the period of measurement. The RFI was investigated in a second experiment based on 384 common female ducks, for which FI, EML, BW, and BW gain were recorded at 39 wk of age. The RFI was determined by multiple regression of FI on metabolic BW and EML. Heritability values of FI and RFI were 0.34 and 0.24, respectively. In addition, if the heritability values obtained for BW (0.65) and BW gain (0.09) were consistent with studies in chickens, the very low EML estimates (0.06) were unexpected. The RFI was strongly genetically linked to FI (Rg = +0.89) but appeared to be independent from BW. Selection based on RFI should therefore reduce the FI of animals without clearly modifying the other components. Moreover, the correlated responses on reproductive traits seem favorable because lower RFI values increase the number of eggs produced per year as well as the hatchability and fertility rates.