By Richard Black BBC science correspondent

Two companies based in the United States have been given government grants of $3m to investigate whether cloned cows could provide a defence against bio-terrorism.

The companies - Hematech and the Dynport Vaccine Corporation - aim to develop animal clones which can produce antibodies to botulinum toxin in their blood.

Botulinum toxin has been developed and used as a bio-weapon in several countries, and the US Government fears it may be used in any future bio-terrorist attack on America.

Nowadays botulinum is usually encountered as a cause of food poisoning. It is also used in cosmetic procedures, in the form of botox injections to smooth wrinkled skin.

But it is, in fact, one of the most powerful poisons known, and has been used in bio-warfare several times.

Safe antibodies

The Japanese army used it during its war with China in the 1930s, and more recently Soviet and Iraqi scientists are also known to have made weaponised versions of the toxin.

An antidote exists, but supplies are scarce, and it can provoke dangerous reactions in the people it is meant to save.

By cloning cows which contain a number of human genes in their DNA, Hematech and Dynport hope to produce antibodies to botulinum which are totally safe for humans.

The cows would produce proteins in their blood, potentially in large enough quantities for them to be used to protect people who might be exposed to botulinum, as well as to treat anyone who is already affected.

The idea of genetically engineering animals to produce drugs or vaccines in this way - known as pharming - is being explored by several companies for a number of diseases.

But this would appear to be the first time it has been investigated as a specific defence against bio-terrorism.