Phytase improves performance in rainbow trout fed low phosphorus plant-based diets

AB Vista tested an enhanced Escherichia coli phytase on rainbow trout that improves performance when fed on low-P diets while enhancing phosphorous and protein utilization and lessening environmental pollution.

October 24, 2019

AB Vista and AB Agri performed two studies to evaluate the effect of phytase supplementation on the overall performance and nutrient retention efficiency of rainbow trout (Oncorhynchus mykiss) fed low-phosphorus (P) plant-based diets at water temperatures of 11 °C and 15 °C.

In the first experiment (11°C), trout (average weight 56g) were allocated to one of four dietary treatments, with three replicate 200L tanks per diet and 35 fish per tank. In the second experiment (15°C), trout (average weight 42g) were allocated to one of three dietary treatments, with three replicate 200L tanks per diet and 34 fish per tank. Diets were fed to satiation over a 75 - 83 day period for experiment 1 and 2, respectively. Treatments included a low-P diet (NC), with no added monocalcium phosphate (MCP), supplemented with 0, 500 or 2500 FTU/kg phytase (AB Vista, Quantum Blue). Experiment 1 also included a diet adequate in P (PC) with 1.8% MCP inclusion.

In both experiments, feeding phytase linearly increased weight gain of fish fed NC diets. Feeding phytase at 2500 FTU/kg improved weight gain of fish exposed to water temperatures of 11°C and 15°C by 36% and 45%, respectively, compared to the respective NC.

Researchers found that feed conversion ratio (FCR) was also improved by 14% with phytase supplementation at 15°C. At water temperatures of 11°C, supplementing phytase to the NC diet improved N retention beyond that of the non-supplemented NC and PC diets. Furthermore, 2500 FTU/kg phytase increased P digestibility by 56 and 27 percentage points, and P retention by around 29 and 17 percentage points, compared to the NC and PC, respectively.

Consequently, supplementing 2500 FTU/kg phytase reduced N and P excretion by 13% and 55%, respectively, compared to the PC. At 15°C, addition of phytase to the low-P diet increased N and P retention in trout by approximately 4 and 24 percentage points, respectively. Supplementing phytase to the low-P diet reduced N and P excretion in trout, with addition of 2500 FTU/kg lowering excretion of these nutrients by 19% and 42%, respectively.

Researchers said that these findings demonstrate the efficacy of an enhanced Escherichia coli phytase, even at low water temperatures, to support performance of trout fed low-P diets, while enhancing P and protein utilization and lessening environmental pollution.

Read full study here.