Genetic modification and cloning of farm animals

Since farm animals were domesticated thousands of years ago, the genetic make-up of animals has changed enormously. Breeders have manipulated thousands of genes to improve traits such as milk yield, wool production and growth. Traits such as fertility and disease resistance have been difficult to improve because they have low inheritance or are difficult to ascertain and breed for.

The technology

Genetic modification was first achieved in mice in 1980 and in farm animals in 1985. It entailed a single gene from the same or different species being injected into a singlecelled embryo. The resulting animal has the injected gene in its cells and passes that gene onto its offspring. The resulting animals were called ‘transgenic’. GM did not initially work for all genes and in early experiments just 1% of injected embryos became viable transgenics.

Since 1985 there have been significant developments in GM experiments which make GM’s use in farm animals more feasible. Improvements have been made in manipulating embryos, which increases the technology’s efficiency, and in the use of cell-based methods (such as embryo stem cells) which allow specific genes to be added, modified or replaced. Another major advance has been in sequencing DNA of animals, which involves identifying all the genes and their functions.

There are around 22,000 genes in mammals which each produce proteins or other factors which interact in different ways. It will be many years before a complete understanding of how the various genes control complex traits such as animal growth, but in areas such as fertility and disease resistance some genes have been discovered which can be effectively used.

Some variation in these genes may be naturally-occurring in some breeds, but where natural variation cannot be found, it could – in principle – be produced in a lab and introduced into the animal with GM. However, until we have a more complete understanding of which genes affect commercially-important traits, GM technology 0 which requires definitive knowledge on individual genes – is likely to be of limited use.

Practical applications of GM technology in livestock

A number if novel uses of GM have been developed, to deal with challenges in animals which cannot be resolved by conventional selective breeding, including:

1. The University of Guelph in Canada has produced a GM pig containing a phytase gene, which it calls ‘Enviropig’. These animals reportedly secrete an enzyme in their saliva which allows them to digest plant phosphorus more effectively, reducing feed costs. They also produce manure with less phosphorous than conventional pigs, reducing the contamination of water sources.

2 A group at China Agricultural University in Beijing have recently reported that they have produced a GM pig that has significant resistance to infection by Foot and Mouth Disease Virus. Although such a pig would not prevent an outbreak of FMDV, it might produce a major reduction in virus transmission and control an epidemic.

ANIMAL BRIEFS – Genetic modification and cloning

3. Many diseases of farm animals are zoonotic, infecting humans. In fact many new human diseases arise from farm animals; one such was the H5N1 avian influenza virus (AIV), which caused considerable concern. Recently the Roslin group have produced GM chickens that do not transmit AIV once they have been infected.

Cloning

Cloning technology was developed in 1995 as a method to improve the efficiency of GM technology. The idea was if embryo cells could be successfully manipulated and grown in culture before being introduced to an embryo, the success rate could be 100%. This would lower the cost of the technology lower and make more feasible in farm animals. It was later realised cloning could also be achieved from adult cells, and in 1996 Dolly the sheep was produced from mammary gland cells. This opened up a new possibility of cloning high-performing farm animals. This would not be a form of GM technology as no
genes have been modified. It would, however, allow limitless replication of on animal.

Because of difficulties with the technology and its so-far low success rate, major commercial cloning efforts have been in the US with prize beef cattle and high-yielding dairy cows. There have also been animal welfare issues as a proportion of animals have abnormalities. Although the surviving animals appear healthy and the problems vary from species to species, these issues will have to be overcome before the technology can be used routinely.

Regulation

Concerns have been raised in recent years over the production of GM animals, ranging from ethical issues of ‘playing God’ to animal welfare concerns about the technology, and potential environmental problems of ‘contaminating’ other farm or wild animals.

At present there are no GM or cloned animals used for food production within the livestock industry in the UK, as it is not permitted to use cloning to produce food in the EU. From the growing number of novel uses of GM animals, it may not be long before one is permitted. For the purposes of research only, their production is considered as an ‘experimental procedure’ and is closely regulated in the UK by the Home Office and governed by both UK and European Legislation.

Currently, any products derived from GM animals are considered to be ‘novel food’, which is regulated in the EU by the European Food Safety Authority and in the UK by both the Advisory Committee on Novel Foods and Processes and the Food Standards Agency.
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Animal Briefs is an initiative of The British Society of Animal Science, providing factual and impartial information on matters of topical concern.

This brief has been prepared by Professor Grahame Bulfield, Emeritus Professor of Animal Genetics, The University of Edinburgh, for the Society.

For further information on this or any related matter, email bsas@sac.ac.uk