Effects Of Pretreatment With Microbial Phytase On Growth Performance And Phosphorous Utilization Of Nile Tilapia (Oreochromis Niloticus)

Four pre-treatment trials were conducted to treat soybean meal, wheat meal, corngluten meal and mixed plant meal (soybean meal, wheat meal and corn gluten mixture)with phytase to determine the optimal dose of phytase. For the first three meals, thegraded addition dosages of phytase were all at 0, 500, 750, 1,000, and 1,500 U/kg,respectively. For the mixture meal, the graded addition dosages of phytase were at 0, 500,750, 1,000 and 3,000 U/kg, respectively. Results showed that the available phosphorouslevels increased significantly with the increased doses of phytase in four experimentalmeals, and revealed that the dose of 1,000 U/kg was most efficient among allsupplemental dosages.Based on the pre-treatment trials, all-plant diets were formulated by treating plantingredients using phytase at 1,000 U/kg. The treatment diets were supplemented withmono calcium phosphate (MCP) at 2.5% (Diet 3), 1.875% (Diet 4), 1.25% (Diet 5),0.625% (Diet 6) and 0% (Diet 7) for Nile tilapia as experimental treatments. In addition,there were three controls: one phytase control without phytase pre-treatment nor inorganicphosphorous supplement (Diet 1); one inorganic phosphorous control without phytasepre-treatment but with 2.5% MCP supplement (Diet 2); and one pre-treatment control(Diet 8) without phytase pre-treatment nor MCP supplement but adding phytase directlyto feed ingredients at a dose of 1,000 U/kg by dissolving phytase in distilled water beforepelleting. All experimental diets (both treatment and control diets) were formulated tocontain approximately 36.4% crude protein. The results showed that the diets pre-treatedwith phytase (Diet 3～7) gave better growth performance, feed conversion ratio andprotein efficiency ratio of Nile tilapia than phytase control diet (Diet 1) (P＜0.05).Therewas no significant difference among the diets pre-treated with phytase at doses of 2.5%,1.875% and 1.25% of required available phosphorus (P＞0.05), which resulted insignificantly better performance than those at doses of 0.625% and 0% (P＜0.05).A digestibility trial was conducted at the end of the growth trial. Apparentdigestibility coefficient (ADC) of phosphorous was improved significantly by the phytasepre-treatment (P＜0.05). No significant difference was detected on ADC of crude proteinamong all experimental diets (P＞0.05).It can be concluded from the present study that phytase can be used to efficientlypre-treat all-plant based diets at a dose of 1,000 U/kg while inorganic phosphorus can besupplemented at 1.25% of MCP to ensure that the adequate amount of phosphorus isavailable to juvenile Nile tilapia, meanwhile to improve their feed efficiency, fish qualityand chemical composition, and thus enhance phosphorous utilization and phosphorousretention.