Phosphorus plays an important role in animal growth, especially for bone formation. In current feed, inorganic phosphorus (MCP, DCP) is commonly used to fulfill needs of fish. Phytic acid, is found in plant and constitutes an unused reservoir of phosphorus in feeds. Furthermore, phytic acid is an antinutritional factor affecting other nutrients such as amino acids, or minerals availability by binding them .
TECHNA tested 3 different phytases in feed deficient in phosphorus to evaluate their effects on digestibility and zootechnical parameters on Gilthead seabream (Sparus aurata), at the Hellenic Centre for Marine Research (HCMR). Phytase, named G, H and K for confidentiality comes from different phytase suppliers.
Six diets were designed for this experiment, three controls with varying level of phosphorus (0.3, 0.45 and 0.6% digestible phosphorus), designed to validate the phosphorus dose response. Three test diets with the same formula as the 0.3% digestible phosphorus value plus the addition of phytase. Phytase levels in feed were calculated based on supplier recommendation and therefore differ (1000 to 1500 FTU or u/g). All feeds were similar for 98% of their composition. M onocalcium phosphate was used for the 0,6% digestible phosphorus diet and replaced by c alcium carbonate partially or fully to reach 0,45 and 0,3% feeds.
In HCMR facilities, 40 seabreams with an initial weight of 16.2 ± 0.04g were stocked in tanks filled with salt water at a temperature of 23-25°C. Each treatment was done in triplicate. The growth phase lasted 76 days and was followed by a two-weeks digestibility phase.
Phosphorus ADC was improved in diets containing phytase G and K compared to its respective control (Negative or 0.3%).
The results showed that the higher the phosphorus was, the better were the performances (FCR and final weight). Only phytase G had higher final weight but remain closer to negative control than intermediate control (expected growth).
In conclusion, even if phytase were able to increase phosphorus digestibility, it was not sufficient to improve growth and FCR to the expected value. Digestible phosphorus valorization following this trial result was far from the supplier’s recommendation (0.15% digestible phosphorus).