Lipid-based protein sparing in juvenile whiteleg shrimp (Penaeus vannamei Boone, 1931) under reduced-protein diets and the limits of functional additives

Dietary protein is the primary cost and environmental driver of shrimp feeds, motivating efforts to enhance protein utilization through lipid substitution and functional additives. Despite extensive interest in reducing dietary protein through lipid-based energy substitution, the physiological limits of protein sparing in whiteleg shrimp ( Penaeus vannamei , Boone, 1931) remain poorly understood. This study evaluated whether lipid-based protein sparing could be achieved in juvenile P. vannamei using a blend of lipid-utilization additives. Two feeding trials were conducted under intensive recirculating conditions. Trial 1 evaluated four dietary treatments consisting of a high-protein low-lipid diet and a reduced-protein high-lipid diet, each with or without additive supplementation (choline chloride, L-carnitine, glycerol monolaurate, and lysophospholipids). Trial 2 assessed additive effects under a nutritionally adequate high-protein diet. Growth performance metrics, including feed conversion ratio, specific growth rate, weight gain, survival, and condition factor, were unaffected by dietary treatments. Reduced-protein high-lipid diets did not improve growth and resulted in significantly lower whole-body protein content and increased lipid deposition regardless of additive inclusion, indicating that protein sparing did not occur. Under adequate dietary protein supply, additive supplementation significantly improved protein efficiency ratio and reduced whole-body lipid accumulation, demonstrating enhanced nutrient utilization efficiency rather than growth promotion. Apparent protein and lipid retention exhibited positive but non-significant responses to additive supplementation, while salinity stress tolerance remained unchanged. These findings demonstrate that dietary protein adequacy, rather than additive supplementation, was the primary determinant of nutrient utilization efficiency. Protein reduction in P. vannamei feeds is therefore constrained by macronutrient balance, emphasizing the importance of nutrient partitioning and metabolic indicators in evaluating sustainable feed strategies.