The effects of excess non-phytate phosphorus from dicalcium phosphate or phytase supplementary sources on performance in laying hens fed reduced-protein diets

The rapid growth of industrial egg production has intensified environmental and economic pressures, prompting the adoption of reduced crude protein (CP) diets supplemented with amino acids to lower costs and nitrogen waste. However, CP reduction may limit phosphorus availability, potentially impairing energy metabolism. This study investigates whether adding extra non-phytate phosphorus (NPP) from mineral (dicalcium phosphate, DCP) and enzymatic (phytase) sources can improve performance, nutrient use, and egg quality in hens fed reduced-CP diets. A total of 528 Hy-Line W36 hens (50 weeks old) were used in a 2 × 5 + 1 factorial design. The CP levels included 14 % and 15 % (2 % and 1 % below the recommended level), and excess NPP treatments consisted of: no additional NPP (recommended NPP level), 1 and 2 g/kg extra NPP via added DCP, and 1.6 and 2 g/kg extra NPP via phytase supplementation (250 and 500 FYT/kg). A control diet containing 16 % CP (recommended CP level) was included as the eleventh treatment. Key findings showed phytase at 250–500 FYT/kg significantly improved egg production, egg mass, and feed conversion ratio compared to unsupplemented diets. Notably, 500 FYT/kg phytase enhanced digestibility of gross energy, CP, ether extract, and calcium, whereas inclusion of NPP from DCP reduced calcium digestibility. Interactive effects between CP and excess NPP were observed: 500 FYT/kg phytase in 15 % CP diets improved P digestibility and eggshell strength, while both phytase levels increased eggshell thickness. In conclusion, phytase supplementation improved laying hen performance in reduced-CP diets through extra-phosphoric effects, while excess NPP from DCP was ineffective.