Development and evaluation of low-phytate wheat germplasm to reduce diffuse phosphate pollution from pig and poultry production units

Abstract

The aim of this project was to reduce phosphate pollution from monogastric farm animals by changing the availability of phosphate from wheat. Currently a lot of wheat derived phosphate is stored in a non-available form, as phytate. The approaches taken in this research project were to: i) determine the effect of high available phosphate (HAP) wheat on phosphorous excretion in pigs and poultry ii) develop a model for quantifying the effect of HAP wheat on diffuse pollution reduction iii) develop adapted wheat germplasm, iv) development of a toolkit for marker-assisted breeding of the HAP trait and v) determine the effect of P fertiliser treatment on the growth and phosphate metabolism of HAP wheat.

Five feeding trials were undertaken using both pigs and poultry to demonstrate the potential reduction in phosphate excretion when HAP wheat was used in formulated diets. The animal performance was not as anticipated, with poultry showing an apparent increase in the availability of P when conventional wheat was fed but with a reduced total P content in the diet (as a result of reducing the amount of inorganic P added to the diet). However, the results were confounded by differences in the protein contents of the HAP and conventional wheat. Specialised diets were therefore produced to start understanding the potential mechanisms involved. The results demonstrated that under certain conditions, P excretion could be reduced in both pigs and poultry using HAP wheat. This can also be achieved (in poultry) using conventional wheat, and reducing the amount of dicalcium phosphate added to the diet. However, when this was done, the growth rate of the birds was reduced.

Using the data from our feeding trials it can be calculated that, by replacing conventional feed with a low phytate alternative, it would be possible to reduce P load to GB waters by 0.53% (321 tonnes P per year) and the agricultural contribution to the total P load to GB waters by 2.73%. As the low availability of phytate P is a feature of digestion in all monogastric animals, it could be envisaged that the development of HAP wheat would also have an impact on P excretion in both the industrial fish farming and human nutrition sectors.

Adapted wheat germplasm was developed using three different techniques. This has provided germplasm with several different mutations resulting in the reduction of phytate and potentially an increased uptake of phosphate. Within the period of the project, full characterisation has not been possible but adapted material has been developed. The development of the toolkit for marker-assisted breeding will improve the efficiency of this process.

There was no evidence for altered performance or need for altered agronomy with HAP wheat. This will need to be confirmed with the UK adapted material and the new mutations. However, since phytate is associated with Fe, Zn etc., the micronutrient levels should be monitored when new germplasm is developed as changes were seen in the analysis conducted on the US variety.

Although significant advantages were shown with the use of low-phytate wheat (LPW) in this project the value of such a commercial development has been superseded by other technologies. The production cost and efficacy of phytase enzymes has improved, such the cost of adding these to formulated feeds for monogastrics is very cheap. In addition, the pig breeding industry has developed GM pigs, modified to produce phytase in their saliva. The plant breeding industry, therefore, considers that the development of a commercial LPW variety would provide no competitive advantage and that the development of other traits would be a better use of their efforts.

However the lines developed in this program are still of interest in some third world countries where human diets are generally poor and changing the availability of micronutrients has significant health benefits.