Genetic parameters of slaughter traits measured on Greylag geese after induction of spontaneous liver steatosis

Previous studies have demonstrated the possibility of inducing hepatic steatosis in geese without resorting to force-feeding, although results were highly variable. The aim of this study was to estimate the genetic parameters of traits of interest for the foie gras industry (liver weight and carcass cut weights) obtained after induction of steatosis without force-feeding. This represents a preliminary step towards designing a breeding programme aimed at producing foie gras in a more ethically acceptable way. Two successive experimental flocks, comprising several hundred birds each and derived from a commercial population in 2020 and 2021, were subjected to the induction protocol: feed restriction until 16 weeks of age, followed by ad libitum maize feeding for 10 weeks, during the autumn, in closed facilities with controlled lighting. The populations included nearly equal numbers of males and females, and no significant difference in liver weight was observed between sexes, which is an additional advantage for selection and production. Estimated heritabilities were high (0.56 ± 0.10 for liver weight, 0.45 ± 0.10 for thigh weight, 0.69 ± 0.11 for breast muscle weight), indicating strong potential for improvement of these traits through selection. Moreover, the genetic correlations between liver weight and other traits of interest were either favourable or negligible, particularly with carcass weight (0.62 ± 0.12) and thigh weight (0.69 ± 0.11). Growth traits were also heritable (> 0.6 for BWs at 9 and 14 weeks), with BW gain between these ages moderately heritable (0.33 ± 0.04) and positively correlated with liver weight (0.48 ± 0.14). These results highlight the potential of implementing selection for foie gras production without force-feeding. In addition, an empirical scoring system for liver appearance was also evaluated as a simple alternative to advanced phenotyping tools. This rapid visual classification proved highly heritable (0.67 ± 0.11) and displayed the same favourable correlations with other traits as liver weight itself. This suggests that visual scoring could even replace direct liver weighing in selection programmes, at least in the early stages, thus offering breeders a fast and inexpensive method to identify families with a greater predisposition to hepatic steatosis. Overall, these findings open the way to more sustainable and welfare-friendly foie gras production, in line with societal expectations on animal welfare, while offering breeders practical tools to initiate selection in commercial populations.