EXTRACTS FROM "THE REPORT OF THE COMMITTEE TO CONSIDER THE ETHICAL IMPLICATIONS OF EMERGING TECHNOLOGIES IN THE BREEDING OF FARM ANIMALS", 1995 (THE BANNER REPORT)
4.84 Multiple genetically identical animals can be produced by cloning. This is done in four ways, as follows.
(a) When the embryo has reached the 8-16 cell stage it can be broken down (disaggregated) into individual cells, each one capable of developing into a full embryo, which can then be transferred to a recipient. This process is inefficient because not all the cells develop and therefore is not used commercially.
(b) A more successful cloning technique is to cut the embryo in half (embryo splitting) and transfer each half to a recipient. The result is identical twins.
(c) Another way of cloning, still at an experimental stage, is nuclear trans-plantation. Embryos of slightly larger size (16-64 or more cells) are disaggregated to individual cells and the genetic material from each cell transferred to a mature egg which has had its own genetic material removed. The aim of this technique is to produce a large number of genetically identical embryos, but it is presently not very successful.
(d) Finally, certain cells known as embryonic stem cells can be removed from an embryo and multiplied in vitro to provide a source of nuclear material for the nuclear transplantation technique. This is still at an early experimental stage and stem cells have only been found in a limited number of species.
4.85 There are no specific regulations covering these techniques though the transfer of any embryos produced by these means is governed by the Bovine Embryo Collection and Transfer Regulations, 1993.
4.86 There have been problems with embryos produced by nuclear transfer or splitting causing overlarge calves and subsequent calving difficulties and the industry has stopped using these particular techniques for the moment. Concern has been expressed that the production of large numbers of animals which are genetically identical could have implications for the spread of genetic disorders, and for general susceptibility to disease.
4.87 As with IVF, there may be gains to animal welfare if the use of these techniques obviated the need to resort to surgical collection of embryos. However, the problems with over-sized progeny are a serious cause for concern; in cattle the problem is adequately addressed by the Bovine Embryo Collection and Transfer Regulations, 1993, but in sheep and pigs no such regulations obtain, and it is important that they should. We believe regulations we have recommended in paras. 4.59 and 4.63 would cover this point. As regards the alleged risks involved in the production of genetically identical stock, these seem to us to be illusory. Cloning might be used by elite breeders in order to make widely available a commercially superior animal, but genetic variation would be maintained in elite herds so as to allow further genetic progress. Cloned animals will be prey to disease just like any other, but if they showed a particular susceptibility to disease, genetic or otherwise, they would no longer be used. It is in any case unlikely that in the foreseeable future cloning would be used on a sufficient scale to influence the health status of the whole animal population.