Direct and correlated responses to long-term residual feed consumption-based selection in Brown Tsaiya ducks

Improving feed efficiency (FE) in poultry, particularly in laying ducks, has become increasingly essential for reducing production costs and environmental impact. This study investigated the long-term effects of residual feed consumption (RFC)-based selection on FE and production traits in Brown Tsaiya ducks over nine generations. Two lines were maintained: a selected line (S line), which comprised ducks bred for low RFC over nine generations (G0-G9) of selection, and an unselected control line (C line), which comprised ducks bred randomly under identical management conditions. Selection for low RFC led to substantial reductions in RFC, feed consumption, and feed conversion ratio in the S line, confirming consistent genetic progress in FE compared with that in the C line. Phenotypic differences between the two lines emerged from the fourth generation and became more pronounced in subsequent generations. Although RFC exhibited moderate heritability and strong positive genetic correlations with feed consumption and feed conversion ratio, its relationships with reproductive traits were generally weak. However, the long-term selection response revealed an unfavorable correlated decline in egg mass and egg weight, reflecting a genetic antagonism, confirmed by a highly positive genetic correlation (r_g = 0.566) between RFC and egg mass found in the selected line. Furthermore, the S line exhibited reduced additive genetic variance and increased inbreeding over generations, suggesting the accumulation of selection pressure and narrowing of genetic diversity. Despite these challenges, the S line continued to improve in FE without reaching a genetic plateau, highlighting the potential for further genetic gain. These results establish RFC as a valuable selection criterion for enhancing FE in laying ducks but underscore the need for balanced breeding approaches. Incorporating multitrait or restricted selection indices may help sustain both FE gains and egg production performance, ensuring the long-term genetic and economic sustainability of Taiwan's Brown Tsaiya duck population.