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SYNERGISTIC EFFECTS OF PROTEASE WITH XYLANASE AND PHYTASE ON DIGESTIBILITY AND GROWTH IN TILAPIA (Orechromis niloticus x O. mossambicus)

Janielle Wallace,  Francis Murray and Dave Little
Institute of Stirling, University of Stirling, Scotland FK9 4L; janielle.wallace@stir.ac.uk  

Replacing fishmeal (FM) with higher inclusion of plant-based proteins for aquafeeds may have negative impacts of fish performance due to lower digestibility and anti-nutritional factors. In response, feed-grade enzymes can be used to break down complex feed matrices, improve the nutritive value of "stubborn" ingredients and neutralize anti-nutritional factors. This becomes more important as average FM inclusion for tilapia diets fall below 2% in 2015.

Methods: This study was designed to evaluate the effects of protease with xylanase and phytase on growth performance in tilapia fed 2% FM diets. Two basal diets (28% CP) were formulated to contain FM at two inclusion levels (2% and 10%), the negative and positive controls respectively.

Growth: 600 fish (71.1g ± 10.9 STD) were stocked in 30 1m3 pond-based cages. Six replicate groups were fed the five treatments twice daily to apparent satiation for 85 days. Productivity and economic factors (ADG, feed intake, FCR, TGC, survival, ΔU) were used as key response variables. Proximal intestines were collected for histomorphology.

Digestibility: 10 fish (113.3g ± 7.31 STD) were stocked in 15 (650 L) static tanks. The five treatments were randomly assigned to three replicates each and fish fed three times daily to apparent satiation for 56 days. Fish and faecal material were collected for analysis

Research Impact: Based on the findings, ternary combinations of protease with xylanase and phytase has potential benefits in low FM diets for tilapia production The study confirmed the additive effect of protease on feed intake and FCR (P<0.05). Biologically, 2% FM diet supplemented with low protease inclusion (0.2 g/kg), xylanase and phytase produced comparative performances to an average 10% FM diet yet, economically a higher dosage (0.4 g/kg) was more profitable. Protease improved villi length but had no additive effect on P, lipid and energy compared to NOPRO (no-protease) diet.










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