- Much of the phosphate in plant derived animal feed is locked up in a relatively inaccessible form called phytate.
- Phytate is inositol hexaphosphate phosphate (inositol is a sugar and it has six phosphate groups bound)
- Phytate is a major storage form of phosphate in plant cells and therefore animal feed derived from plants (grain) is rich in phytate
- Phytate is a major cause of pollution because animals cannot efficiently digest phytate. It is therefore passed through the gut into the excrement.
- Pig muck therefore can contain very high levels of phytate.
- Phytate in manure is then broken down by bacteria. This releases large amounts of phosphate into the soil and ground water.
- A scientist from Dow AgBiotech told me that being able to get rid of phosphate/phytate-rich manure is the major limitation for pig production.
- Farmers tend to spread this manure on their land and there is therefore an upper limit on what they can spread.
- Decreasing phytate concentrations is feed grain is an important trait for cereal breeding - low phytate containing maize have been bred (I'm not sure if they are commercially used)
Results reported in this paper:
This paper describes an alternative approach – generating transgenic animals that can break down phytate. The technology used seems to be pretty routine. An E. coli (bacteria) gene encoding the enzyme phytase which releases phosphates from inositol hexaphosphate was introduced into pigs. This gene was expressed in the salivary glands resulting in the expression of phytase in the saliva.They showed that these animals can access sufficient P in their diet in the absence of dietary P. That is they can get their P requirement from phytate.
NB: as regards the ethics of GM breeding in relation specifically to animals, any thoughts, or links to relevant papers -on all sides of the debate - would be much appreciated.