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Control of diffuse phosphate pollution

Control of diffuse phosphate pollution from pig and poultry production units using a low–phytate wheat based feed

Contact:Steven Bentley

This project aims to facilitate reduction of diffuse pollution though production of new feedstuffs. The consortium will initiate production of wheat germplasm with a low phytate composition in the grain, thus increasing bioavialability of phosphate to animals with monogastric digestion. This will reduce the level of phosphates entering the environment from animal wastes. The consortium will map the genes involved in this character and will seek to understand the plant physiology underlying changes in phytate content, together with related mineral nutrition. The effect of changes in feed quality will be determined through feeding studies and the net effect on the environment and diffuse pollution modelled.

The major form in which phosphorus occurs in plants is myo-inositol-1,2,3,4,5,6-hexakisphosphate, commonly referred to as phytic acid, inositol or InsP6. It is an important anti-nutritional factor to farm animals due to its ability to complex micro-nutrients such as iron and zinc. It occurs in different tissue, but accumulates in large amounts in the seeds, where it serves as a storage form of myo-inositol and phosphorus for utilisation during seed germination and seedling growth. Much progress has recently been made in understanding the biosynthesis pathway from the analysis of mutant lines exhibiting a low phytic acid (lpa) phenotype. Studies on maize and soybean in particular and to a lesser extent in barley have shown that lesions in several distinct gene classes can lead to lower levels of seed phytate.

Microbial-derived phytase can be added to the diets of pigs and poultry and this in now an important part of feed enzyme markets. This phytase will break down some of the phytate in plant-derived feeds, thereby rendering the P, as well as other minerals and certain proteins, available to the animal. By using a balance of nutrients combined with phytase, the livestock industry in the Netherlands has more than halved the amount of P excreted by growing and finishing pigs over the last 20 years. However, these beneficial effects of microbial phytase are adversely affected by a low ratio of calcium:total phosphorus. Since the calcium content of layer hen diets is high, phytases are not normally added. In the UK, circa 35% of the total 500,000 sows, are outdoors. Waste output is diffuse, cannot be removed and is not used on any particular crop. They are generally on a site for two years, then moved on; in one year, these sows consume 150 thousand tonnes of wheat. Total pig output in the UK in terms of number of pigs is 9.5m/annum; consuming 2.7m tonnes of feed ( 50-55% wheat). It is estimated that approximately 9,720 tonnes of P2O2 is excreted by pig/year in the UK.

The consortium has completed initial work on the development of new wheat germplasm with a low-phytate content. New lines have been developed, where Phytic acid P represents only 42% of seed total P, in contrast to 74.7% of seed total P in the spring-sown control or a 35% increase in the phosphate that would be available to a monogastric animal.

Funding: Sponsored by Defra through the Sustainable Arable LINK programme; The Home Grown Cereals Authority and industrial support.

Collaborating Organisations: University of Reading; Velcourt Ltd; Nickerson-Advanta Ltd; Harper Adams University College; University of Idaho; University of Nottingham; Frank Wright Ltd; Meat & Livestock Commission/BPEX; ABNA Ltd; Sun Valley Foods Ltd; Deans Foods Ltd; JSR Farms Ltd; British Poultry Council Ltd; Anglian Water Services Ltd; The Environment Agency