Introduction: Today, the use of enzymes to improve feed digestibility and achieve higher productivity has been considered as an effective strategy in the poultry industry. Phytase is an enzyme that is used in most commercial diets with the aim of breaking the bonds of phytic acid to increase the digestibility and absorption of nutrient. On the other hand, by carrying out breeding programs and subsequently reducing resistance to diseases due to the shift of nutrient for more production, more attention has been paid to immunity system and gut health. Therefore, gut health has a key role in the absorption of nutrient resulting from the activity of endogenous and endogenous enzymes. Hence, research in term of gut health modifiers such a prebiotics, probiotics, postbiotics, parabiotics and essential oils have increased. Among them, phytogenics have become more popular nowadays. Phytogenic supplements are known as their role on growth performance and increase profitability through improving microbiota balance and intestinal health. In addition to dietary phtoygenic supplemets, dietary calcium and phosphorus reduction is probablely effective tool led to phytase activity released nutrient. Results from studies have been showed that, slight decrease in the level of calcium and phosphorus is effective in increasing the efficiency of these mineral and gut health via reducing gut acidity. In the present study, effect of high amounts of phytase in combination with phytogenic additive in diets with reduced calcium and phosphorus on nutrient digestibility, humoral immunity and some related blood parameters of broiler chickens were investigated.
Materials and Methods: The 672 one-day-old male broilers of Ross 308 strain were assigned to 12 dietary treatments and four replicats in a 2x2x3 factorial arrangement with different amounts of phytase (zero, 500 and 2000 FTU) and two levels of phytogenic supplement (zero and 200 mg/kg of feed) on two dietary calcium (normal=0.81, 0.72, 66%; reduced=0.71, 0.62 and 0.56% for different phases) and phosphorus (normal = 0.36, 0.32 and 0.29%; reduced=0.31, 0.27 and 0.24% for different phases) in a completely randomized design.
Results and Discussion: Addition of phytase to the diets in combination to calcium and phosphorus reduction increased phosphorus digestibility compared to that normal diets (P<0.05). Increasing phytase from 0 to 500 and 2000 FTU increased digestibility of dry matter, organic matter, phosphorus, calcium and protein (P<0.05). The interaction effect of adding phytase enzyme along with decreasing the amount of calcium and phosphorus on the digestibility of calcium and phosphorus were significant (P<0.05), and the inclusion of phytogenic supplement at the levels of 500 and 2000 FTU of phytase per kg of feed increased phosphorus digestibility (P<0.05). Decreasing dietary calcium and phosphorus concentration and adding phytogenic additive, improved nutrient digestibility of nutrients except protein (P<0.05). Inclusion 2000 FTU of phytase in diets increased digestibility of nutrients and decreased blood calcium compared to the usual amount and diet without phytase (P<0.05). The blood concentratin  of alanine aminotransferase reduced by 2000 FTU of phytase compared to 0 and 500 FTU (P<0.05). Dietary addition of phytase decreased alkaline phosphatase (P<0.05). High levels of phytase inceasded total serum immunoglobulins at the age of 28 and 41 days compared to the zero level (P<0.05), but there was no difference compared to the 500 FTU. Addition of phytase or phytogenic supplement improved antibody level against Newcastle at the age of 41 days (P<0.05).
Conclusion: Based on the results of this research, 2000 FTU phytase compared to 500 FTU and adding phytogenic supplement had positive effects on nutrient digestibility, growth performance and immunity in broilers.