Effects of phytase supplementation on energy and nutrient availability, and phytate degradation in turkeys

The study aimed to investigate the effect of graded levels of supplementary phytase (PHY) on energy and nutrient availability, and phytate (IP6) degradation of rapeseed meal (RSM) containing, wheat-based diets in turkeys. A control diet containing 6.8 g/kg available P (positive control; PC), a low-P diet containing 5.3 g/kg available P (negative control; NC) and a diet produced by mixing 810 g of the NC with 190 g industry produced RSM containing 5.6 g/kg available P (RSM diet) were produced. The NC and the RSM diets were then split in four parts each and PHY was added at 0, 500, 2500 and 12500 FTU/kg, respectively, resulting in nine diets in total. Feed intake (FI), weight gain (WG), and feed conversion ratio (FCR), from 27 to 35 d age, AMEn, retention coefficients for dry matter (DMR), nitrogen (NR), fat (FR), Ca (CaR), P (PR) and the profile of inositol phosphate esters (IP3-6) and myo-inositol (MYO) in excreta were determined. There was a positive quadratic relationship (P < 0.05) between dietary PHY activity and daily FI, as dosage of 2500 FTU was the optimum for FI. Feeding RSM reduced daily weight gain (P < 0.05) and feed efficiency (P < 0.001). Dietary AMEn increased linearly with PHY supplementation (P < 0.05) although feeding RSM reduced (P < 0.001) AMEn. Compared to NC, the PC had greater AMEn, DMR, CaR, PR, (P < 0.001) and NR (P < 0.05). Dietary CaR and PR linearly increased (P < 0.001) with PHY dosage which coincided with a decrease in IP5 and IP6 isomers (P < 0.001). The response to PHY followed curvilinear shape for IP4 (P < 0.001) and IP3 (P = 0.001) isomers.