Abstract
Nutritional equations are essential tools for planning precise feeding strategies in poultry production. For Japanese quails (Coturnix japonica), early physiological maturity (around 40-45 days of age) and rapid mineral deposition during initial growth phases demand species-specific models. The factorial method enables accurate estimation of calcium and available phosphorus requirements by partitioning maintenance and growth needs, incorporating metabolic weight (kg⁰(.)⁶⁷) and nutrient utilization efficiency. These equations support sustainable and cost-effective feed formulation. To estimate calcium and available phosphorus requirements for Japanese quails during the starter (1-14 days) and grower (15-35 days) phases using predictive equations based on body weight, daily weight gain, and mineral retention efficiency. Two experiments were conducted with 655 female quails subjected to graded feeding levels (25 % to 100 % ad libitum). Maintenance requirements were determined via comparative slaughter and regression analysis between intake and retention. Gain requirements were estimated through serial slaughter and carcass composition analysis. Nutrient utilization efficiency was incorporated into the equations to calculate dietary requirements. Maintenance requirements increased with age: calcium from 60.86 to 223.58 mg/kg⁰(.)⁶⁷/day and available phosphorus from 43.18 to 106.35 mg/kg⁰(.)⁶⁷/day. Gain requirements were 24.91 mg/g/day (Ca) and 14.12 mg/g/day (Ap) in the starter phase, and 15.67 mg/g/day (Ca) and 8.48 mg/g/day (Ap) in the grower phase. Older quails showed higher mineral retention efficiency (71 % Ca; 73 % P), reducing dietary demand compared to previous studies. Reliable equations were developed: Ca = 60.86 × + 24.91 × WG (starter); Ca = 223.58 × W ⁰(.)⁶⁷ + 15.67 × WG (grower). Ap = 43.18 × W ⁰(.)⁶⁷ + 14.12 × WG (starter); Ap = 106.35 × W ⁰(.)⁶⁷ + 8.48 × WG (grower). Where: Ca = Calcium requirements; Ap = Available phosphorus requirement; W = Body weight (kg); WG = Weight gain (g/quail/day). These equations enable precise diet formulation, optimize mineral use, and reduce environmental impact and production costs. They provide a technical foundation for nutritional programs tailored to Japanese quails.