EFFECTS OF MICROBIAL PHYTASE ON THE PRE-TREATMENT OF ALL-PLANT FEEDSTUFF AND REPLACEMENT OF INORGANIC PHOSPHOROUS IN NILE TILAPIA (Oreochromis niloticus) FEED

Cao Ling[1], Yang Yi, Wang Weimin, Amararatne Yakupitiyage, Yuan Derun, James S. Diana

College of Fisheries, Huazhong Agricultural University

Wuhan, Hubei 430070, P. R. China

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This study was conducted at the Asian Institute of Technology to assess effects of microbial phytase on the pre-treatment of plant ingredients and replacement of inorganic phosphorous in Nile tilapia (Oreochromis niloticus) feed.

Two pre-treatment trials were conducted to treat soybean meal and mixed plant meal consisting of soybean meal, wheat meal and corn gluten with phytase at doses of 0, 500, 750, 1,000, 1,500, and 0, 500, 750, 1,000, 1,500 and 3,000 U/kg to determine the optimal dose of phytase, respectively. Results showed that the available phosphorous levels increased significantly with the increased doses of phytase in both soybean meal and mixed plant meal (Y=11.1907 X0.2841, R2=0.9078; Y=29.7048 X0.1457, R2=0.9158; respectively, P < 0.05), and revealed that the dose of 1,000 U/kg was most efficient.

Based on the pre-treatment trials, all-plant diets were formulated by treating plant ingredients using phytase at 1,000 U/kg. The diets were supplemented with mono calcium phosphate at 100%, 75%, 50%, 25% and 0% of the required available phosphorus for Nile tilapia as experimental treatments. In addition, there are three controls: one phytase control without phytase pre-treatment nor inorganic phosphorous supplement; one inorganic phosphorous control without phytase pre-treatment but with 100% available phosphorus supplement; and one pre-treatment control without phytase pre-treatment nor inorganic phosphorous supplement but adding phytase directly at a dose of 1,000 U/kg before feed processing. All experimental diets (both treatment and control diets) were formulated to contain approximately 36.4% crude protein.

Sex-reversed Nile tilapia fingerlings of 0.7–0.8 g in size were stocked in 16 in-door recirculating circular cement tanks (1 m in both depth and diameter) at a rate of 30 fish per tank, and fed with the experimental diets twice daily at 0900 – 1000 h and 1600 – 1700 h to apparent satiation for 60 days. The results showed that the diets pre-treated with phytase gave better growth performance, feed conversion ratio and protein efficiency ratio of Nile tilapia than control diets (P < 0.05).There was no significant difference among the diets pre-treated with phytase at doses of 100%, 75% and 50% of required available phosphorus supplement (P > 0.05), which resulted in significantly better performance than those at doses of 25% and 0% (P< 0.05).

It can be concluded from the present study that phytase can be used to effectively pre-treat all-plant based diets at a dose of 1,000 U/kg while inorganic phosphorus can be supplemented at 50% of the required available phosphorus to ensure that the adequate amount of phosphorus is available to juvenile Nile tilapia.

[1] Presenting author