Effective phytate destruction by phytase will release not only phytate-bound phosphorus, but also other nutrients in the diet that chelate with phytic acid under gastric conditions. To achieve the full economic benefits from phytase, a matrix can be applied to the diet formulation to account for this release of additional nutrients. However, as the dose response curve is not linear, the appropriate matrix values must be assigned to phytase when the inclusion rate varies. The objective of the current study was to validate the phytase (Quantum Blue, AB Vista, Marlborough, UK) matrix for aqua by applying 1500 FTU and 2500 FTU matrix values for available phosphorus (avP), calcium (Ca) and protein to the diets of tilapia.
A total of 750 male tilapia (Oreochromis niloticus; average weight 20g) were allocated to one of 5 diets, with 4 replicate 100L tanks per diet and 32 fish per tank. Water temperature was set at 28±1°C. Plant-based diets were fed to satiation (3 meals a day) over a 12-week period. Treatments comprised a positive control diet (PC) with 0.95% total P, 0.74% Ca and 35.2% protein, a negative control diet with a formulated reduction in 0.20% avP, 0.15% Ca and 0.56% protein (NC1), NC1 plus 1500 FTU/kg phytase (NC1+1500), a negative control diet with a formulated reduction in 0.24% avP, 0.18% Ca and 0.65% protein (NC2) and NC2 plus 2500 FTU/kg phytase (NC2+2500). Productive performance was measured over the 12 weeks and retention was determined through carcass analysis at the end of the study. Data was subjected to ANOVA using the fit model platform in JMP Pro 15.1, with treatment means separated using Student’s T-test.
Feed analysis revealed that the expected downpsec in avP was achieved in NC1 and NC2. Dietary Ca levels were slightly higher than predicted targeted in NC diets, reaching an average 0.15% reduction across all NC diets. Dietary protein was more severely reduced in NC diets than expected, reaching a minimum decrease of 1.4%. Performance of tilapia was worsened with each nutrient downspec (P<0.05; Table 1). Addition of phytase to each respective control increased weight gain of fish and reduced FCR to a statistically similar level as the PC.
Retention of nitrogen and P are shown in Table 1. Nitrogen retention worsened with each nutrient downspec, with NC2+2500 getting back to the PC (P<0.01). Phosphorus retention of phytase fed fish increased beyond all the control diets (P<0.01).
In conclusion, performance of tilapia could be maintained when avP, Ca and protein were reduced in the diet by supplementing phytase at the appropriate dose, thereby validating the matrix values for the commercial phytase tested in tilapia.