Optimization of dietary methionine requirements under aflatoxicosis in quail chicks using response surface modeling

This study aimed to determine the optimal dietary methionine (Met) requirement for quail chicks exposed to different concentrations of aflatoxin B₁ (AFB) using response surface and quadratic polynomial modeling. Previously, excess Met was shown to alleviate the adverse effects of AFB on performance, liver function, and immunity in quail. Here, the same experimental dataset was reanalyzed to quantify Met-AFB interactions and define nutrient optima. Three levels of dietary Met (5.0, 6.0, and 7.0 g/kg) and three levels of AFB (0.0, 2.5, and 5.0 ppm) were modeled across performance, biochemical, immunological, and microbial variables. Model fits were high (R² = 0.62 to 0.95). Increasing dietary Met improved feed intake, gain, feed conversion ratio, and immune indices (hemagglutination inhibition and SRBC titers) while reducing serum hepatic enzymes and malondialdehyde concentration. Methionine supplementation also counteracted AFB-induced dysbiosis by increasing lactic acid bacteria and restoring E. coli balance. The optimized models indicated that dietary Met requirements increased proportionally with aflatoxin exposure, reaching approximately 130-150 % of the NRC (1994) recommendation to maintain performance, hepatic integrity, and immune resilience. These results demonstrate that Met acts as both a structural and functional nutrient under toxin stress. The response surface approach provides a quantitative framework for formulating Met -enriched diets for poultry exposed to mycotoxins.