On one side are animal-rights activists, ethically opposed to the patenting of living beings altogether; on the other, research companies and academics who see potential medical and commercial benefits outweighing animal-welfare concerns.
Recent advances in cloning - as seen in Dolly, the world's first cloned sheep - have encouraged research companies investigating the commercial production of animals with artificial genes, programming them to produce useful chemicals in their milk.
Both sides will seek to influence the European Parliament, which is about to give its second reading to a proposed directive on "the legal protection of biotechnological inventions". It must be agreed both by MEPs and member states in the Council of Ministers to become law.
If a patent law does reach the EU statute book, it will be welcomed by the European Patent Office, which has struggled to pass a backlog of patent applications, slowed by legal actions from environmental groups.
Scientists working for medical, cosmetic and agricultural research companies want the regulation to permit the patenting of biotechnological ideas, thus guaranteeing a return on the time and money spentdeveloping them. However, groups such as Compassion in World Farming (CIWF) want to limit the amount of patents that can be granted, because without the prospect of a patent much biotechnological research would not take place. CIWF fears that animals subjected to genetic experiments could suffer and is contesting a European patent on introducing a cattle growth hormone into pigs, on the grounds that it can cause lameness, impotence, ulcers, poor vision and kidney and liver damage.
It will try to persuade MEPs to strengthen the welfare clause in the directive, which currently states that patents cannot be granted where it would "cause suffering" to animals, unless "substantial medical benefits" to man or beast result. CIWF director Peter Stevenson said he wanted the parliament to add the words "or physical handicaps", which would help his group to challenge the awarding of such patents in the courts.
"It is difficult to prove suffering," he said. "It's a very subjective thing. With a physical handicap, it's an objective thing."
This would be opposed by the Association of Medical Research Charities, which does not want to see UK regulations governing animal research restricted.
The Home Office currently licences experiments on animals after a cost-benefit analysis taking into account the suffering to animals and the potential medical and consumer benefits.
Existing patent applications involving animals that have been considered by the European Patent Office include:
n Collagen, the cosmetic implant that has plumped the lips of "Ginger Spice" Geri Halliwell and Baywatch's Pamela Anderson, could be extracted from the milk of genetically engineered pigs if the US Collagen Corporation gains a European patent.
n The Roslin Institute could gain exclusive EU rights to the nuclear transfer technique that produced the world's first cloned animal, Dolly. It could then licence them to companies hoping to reproduce animals with useful genetic modifications.
n Mothers could wean their babies on the milk of cows implanted with a human lactation gene. Semi-skimmed baby milk could replace powdered formula as the supermarket choice. PPL Therapeutics, of Scotland, have applied for an EU patent.
n Scientists at Imperial College, London, want to patent the production of laboratory animals planted with a DNA strand making them ideal for experiments to detect the cause and cure of male baldness.
n Merck & Co, of New York, has applied for an EU patent for "transgenic fowl" bred with the growth hormone of a cow, which makes chicken fatten faster.Reuse content