Rapeseed cake as a soybean meal substitute in Acheta domesticus diets: productive performance, body composition and economic efficiency under two amino acid supplementation strategies

<title>Abstract</title> <p> The high cost of feed, of which soybean meal is a major protein component, constrains the economic viability of <italic>Acheta domesticus</italic> farming. Rapeseed cake, a locally available European by-product, is a promising alternative protein source, but its comparatively low lysine content raises the question of whether the synthetic amino acid supplementation inherited from poultry feed formulation is necessary to sustain cricket performance. This study evaluated partial soybean meal substitution by rapeseed cake and synthetic lysine and methionine supplementation. Productive performance, body composition and feed cost per kilogram of biomass were assessed over 35 days. Amino acid supplementation had no effect on any productive variable at 0% or 50% substitution, and at 80% substitution its removal significantly increased feed intake, biomass gain and survival. The 80% rapeseed cake diet without supplementation achieved the highest biomass gain (2.42 ± 0.17 g), highest survival (88.9 ± 3.9%) and one of the highest proportions of adults, outperforming its supplemented counterpart. Rapeseed cake accelerated development and increased individual body weight despite lower dietary crude protein, and raised body fat content. Feed cost per kilogram of biomass did not differ significantly among treatments. These results demonstrate that synthetic amino acid supplementation is unnecessary for <italic>A. domesticus</italic> when diets are formulated with soybean meal, rapeseed cake and cereals, and can be detrimental at high rapeseed cake inclusion. Rapeseed cake is thus a viable soybean meal substitute that, combined with removing unnecessary amino acid fortification, offers a simplified, locally sourced feeding strategy for cricket production. </p>