Influence of Dietary Phytase, Lysine and Phosphorus on Nutrient Digestibility, Hydrolysis of Phytic Acid and Coenzyme Q10 Synthesis in Laying Hens

High doses of phytase have been shown to increase phytic acid (Phyt-ac) hydrolysis, nutrient availability and coenzyme Q10 (CoQ10) synthesis in broilers, but no previous reports are available in layers. The present study tested the effects of four doses of phytase (0, 300, 1200 and 4800 FTU/ kg) and three digestible lysine (dLys) levels (0.67, 0.77, and 0.87%) on Phyt-ac hydrolysis, amino acid and mineral digestibility in layers fed diets with 0.12% available P (avP). Additionally, a diet with 0.25% avP and 0.87% dLys, without phytase added, was evaluated as control treatment. CoQ10 content in liver was quantified in the first three doses (0, 300, and 1200 FTU/kg) at the highest and lowest levels of dLys (0.67 and 0.87%). There was an interaction effect (P<0.05) between phytase doses and dLys levels for amino acid digestibility. In 0.67% dLys diets, the response to incremental doses of phytase was linear, while in 0.77% and 0.87% dLys there was a quadratic response (P<0.05). P digestibility was higher with incremental doses of phytase, despite a reduced effect of enzyme in 0.87% dLys diets (P=0.034). No differences (P>0.05) were observed between treatments on availability of Ca, Zn, Cu, Co, Mn and Fe. Phytase inclusion increased Mg, Na, and K digestibility in 0.67 and 0.77% dLys diets, but in 0.87% diets these were reduced (P<0.05). Doses of phytase 1200 and 4800 FTU/kg increased the presence of lower low inositol esters (Ins-P) such as Ins-5P, Ins-3P and inositol (P<0.05). Ins-4P and Ins-2P content was influenced (P<0.05) by phytase addition and dietary dLys. Liver CoQ10 content was similar between phytase doses in 0.67% dLys diets, but in the 0.87% dLys diet, phytase addition reduced coenzyme concentration in liver (P<0.05). In conclusion, phytase dose and dLys level in layer diet affected nutrient digestibility, Phyt-ac hydrolyzes, and CoQ10.