Scientists believe the disease is caused by a breakdown in the protein which coats the nerves in the brain and spinal cord.

Researchers in New Zealand hope that by introducing the human gene that codes for this protein into cows they can make the animals produce the chemical in their milk.

This could then be extracted and purified and used in an experimental treatment for MS sufferers.

Complex cells

AgResearch said it had applied to New Zealand's Environmental Risk Management Authority (ERMA) for permission to undertake a series of experiments on transgenic cattle.

The authority is responsible for compliance with biosecurity and other environmental safety regulations.

Modifying the genetics of farm animals so that they express medically-useful chemicals in their milk has been labelled "pharming". Although bacteria have long been used to make human drugs, there are some complex proteins that can only be produced in the more sophisticated cells of larger organisms.

Cows have an extra advantage in that a single animal can produce 10,000 litres of milk a year. Even at low concentrations, the potential yield of a pharmaceutical is very high.

Small herd

AgResearch is interested in myelin basic protein (MBP). It is thought the patchy degeneration of the myelin sheath that coats nerves in the brain and spinal cord is involved in the development of MS.

"In animals showing clinical signs of the disease, recovery can be helped by ingestion of myelin basic protein," AgResearch scientist Dr Phil L'Huillier said in a statement.

If the MBP from genetically-modified milk proved useful, it could potentially prove to be a breakthrough, he said. AgResearch's proposal involves the production of a small herd of up to 30 cattle for the project, at a secure containment site in the Waikato region of New Zeland.

The application goes before ERMA on Wednesday. Earlier this year, it approved an application from the developers of Dolly the cloned sheep, PPL Therapeutics.