Abstract
ABSTRACTThe study investigated the effect of different levels of dietary Ca, non-phytate phosphorus (NPP) and phytase on the nutrient utilization of broiler chickens. A total of 576 day-old broiler chicks (Ross 308) were offered diets containing 3 concentrations of Ca (6, 8 or 10 g/kg diet), 2 concentrations of NPP (3 or 4 g/kg) and 2 concentrations of exogenous microbial phytase (0 or 500 FTU/kg). Diets with high Ca (10 g/kg) reduced (p < .001) the ileal digestibilities of P and protein. The digestibility of Ca and P was negatively (p < .001) affected by high Ca and low NPP (3 g/kg) diet supplemented with phytase. Phytase improved (p < .001) the digestibility of protein and P and also the retention of P and Ca. Phytase supplemented to diets containing 8 g Ca/kg improved (p < .030) the tissue protein content of jejunal mucosa, but reduced (p < .009) the Ca-ATPase activity. Supplemental phytase elevated the plasma P level, especially in birds fed diets containing 6 g/kg Ca and 4 g/kg NPP. In conclusion, phytase supplementation of diets reduced the excretion of minerals by improving their digestibilities; however, this response was dependent on the concentration of dietary Ca and NPP.
Highlights
Poultry diets comprise mainly cereals and oilseed cakes and contain variable amounts of phosphorus in the form of phytic acid or its salt, phytate
Body weight (BW) and feed leftover were recorded on day 24 on a cage basis for the determination of body weight gain (BWG) and feed intake (FI)
From day 0 to 24, a 3-way interaction of Ca, non-phytate phosphorus (NPP) and phytase was observed for FI, where phytase supplementation to diets with 8–10 g Ca and 3 g NPP/kg reduced (p < .035) the FI of broilers
Summary
Poultry diets comprise mainly cereals and oilseed cakes and contain variable amounts of phosphorus in the form of phytic acid or its salt, phytate. In addition to binding phosphorus, phytic acid forms complexes with other minerals and nutrients in the gastrointestinal tract (GIT) of poultry. Hydrolysis of phytate by phytase is essential to liberate the bound nutrients in the GIT for absorption (Cowieson et al 2004). Poultry diets are commonly supplemented with exogenous microbial phytase for effective dephosphorylation of phytate because of the low endogenous phytase activity (Selle et al 2000). Adding microbial phytase to diets enhances the bird’s growth performance and mineral digestibility, and reduces nutrient excretion to the environment (Selle & Ravindran 2007). It has been reported that microbial phytase supplementation may influence the protein or amino acid digestibility in poultry by releasing the phytate-bound protein and increasing their utilization (Ravindran et al 2000). Controversy exists in the literature on the effect of phytase on dietary apparent metabolisable energy (AME)
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