Abstract
The effect of two microbial phytases at two dose-levels on performance and apparent ileal digestibility (AID) of nutrients in broilers fed European-type diets was studied. A total of 1,200 d-old Ross 308 male broilers were randomly assigned to 5 treatments with 30 birds/pen and 8 pens/treatment. A nutritionally adequate positive control (PC) diet was tested against 4 experimental diets containing reduced total P, retainable P, Ca and Na as per the recommended nutritional contribution for Buttiauxella phytase (Phy B) at 1,000 FTU/kg (-1.87 g/kg, -1.59 g/kg, -1.99 g/kg and -0.4 g/kg vs. PC, respectively). Experimental diets were supplemented with Phy B at 500 FTU/kg or 1,000 FTU/kg, or Citrobacter phytase (Phy C) at 1,000 FTU/kg or 2,000 FTU/kg. Diets were based on corn, soybean meal, rapeseed meal and sunflower meal and formulated by phase (starter 1–10 d, grower 11–21 d) in crumbled or pelleted form. Overall (d 1–21), at 1,000 FTU/kg, birds fed Phy C exhibited lower BWG (-2.7%), FI (-3.4%) and tibia ash (-2.2%) vs. PC (P < 0.05), and reduced BWG (-3.6%), FI (-3.9%) and tibia ash (-1.8%) vs. Phy B (P < 0.05). Phy B at 1,000 FTU/kg and Phy C at 2,000 FTU/kg maintained performance equivalent to the PC. Digestibility of Ca did not differ among phytase treatments but at 1,000 FTU/kg AID P was greater with Phy B than Phy C (72.3% vs. 62.7%, P < 0.05). Ileal phytate (myo-inositol hexakisphosphate, IP6) digestibility was greatest with Phy B at 1,000 FTU/kg which was higher than Phy C at 1,000 FTU/kg (87.6 vs. 60.6%, P < 0.05). The findings indicate a higher phytate degradation rate of Phy B than Phy C at equivalent dose-level and this is correlated to the performance of the broilers.
Highlights
The anti-nutritive effects of phytate in commercial broiler diets are well recognized and have been extensively reviewed [1,2,3]
Ross 308 male broilers were obtained on day of hatch from a local commercial hatchery where they had been vaccinated against infectious bronchitis and assigned to floor-pens on the basis of body weight (BW), so that pens contained birds of approximately equal average bird weight
Analyzed phytase activities were less than 50 feed. One phytase unit (FTU)/kg in the positive control (PC) diets, suggesting no cross-contamination among control and phytase-supplemented diets, and were within 20% of target values in all experimental diets except the grower phase diets for the 500 FTU/kg Phy B and 2,000 FTU/kg PhyC treatments, where analyzed values were 27% higher than target values (Table 2)
Summary
The anti-nutritive effects of phytate (the salt form of phytic acid, inositol-6-phosphate, IP6) in commercial broiler diets are well recognized and have been extensively reviewed [1,2,3]. They arise due to the limited ability of monogastric animals to digest phytate, and its ability to bind with minerals and proteins in the gastrointestinal tract (GIT). This can markedly reduce the bioavailability of not just P, and other key minerals, amino acids and protein [4], and can impair bird performance and increase excretion of undesirable P into the environment.
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