Over the centuries, animals with new combinations of genes have been produced using conventional breeding methods by means of careful selection of particular animals. The number of new gene combinations that can be achieved in this way are, however, limited since genes can only be shuffled about between members of the same or very closely related species. Transgenesis is a radically new technology for altering the characteristics of animals by directly changing the genetic material. Since DNA contains a universal genetic code for living organisms, it can, in principle, be transferred between completely unrelated organisms to produce organisms with useful characteristics that would not otherwise be available. Many different genes and their actions have now been characterized. This knowledge opens up the possibility of looking for methods of changing genes in ways that are useful, for example to cure diseases or to introduce desirable genes into an animal for a variety of reasons.
During last few decades, a number of different strategies have been used to search systematically for new genes regulating the production of recombinant proteins. These genes with full regulatory system (gene construct) were successfully transferred to the recipient animal and transgenic animals for various genes were produced. The initial work was carried out on mouse and rabbits and was later demonstrated in sheep, goats, pigs and other farm animals. The development of gene cloning and recombinant DNA methods has lead to the production of valuable proteins initially in bacteria, then in eukaryotic cells and now designer animals are being produced. The term transgenic has been used for the first time in eighties to desirable animals harbouring new genes within their genome. It is now used for the characterization of certain variants of a species whose genome has been altered by transfer of outside genes.
Of all the mammals studied by the early scientists, the mouse became the animal of choice, because of its small and convenient size, large litter size, resistance to infection and relatively rapid generation time. Moreover the interesting pool of mutations affecting coat colour and behaviours were of added advantage in the use of mouse system for transgenic animal production. Various methods were used by various workers for manipulating the mouse genome for reintroduction of desired genes. These may be the use of recombinant DNA techniques in various ways. The important techniques for gene transfer include various kinds of vectors (viral), embryonic stem cells, round spermatids and direct micro injection of desired copies of new genes. The latest development in this series is the nuclear transfer of germinal or somatic cells into the recipient oocytes for cloning of animals.
The transgenic animal production has numerous applications in agriculture and animal improvement, production of desired proteins and drugs of pharmaceutical importance. The applications of transgenic animals in medicine are gaining utmost importance. Moreover, these techniques can be extremely useful in the conservation of endangered and rare germplasm. With recent developments in bovine embryology, there is a paradigm shift to extend this working knowledge for the creation of genetically engineered animals and production of transgenic animals. Transgenic technology has great potential in molecular breeding of small and farm animals. This will allow valuable modifications to the genome of virtually any animal. Such technologies will improve agronomic traits and will lead to the introduction of new and lower cost bio- pharmaceuticals and medical procedures.
The number of transgenic animals has increased more than ten-fold (from 48,255 to 511,607) in UK. In contrast, the total number of animals used in all areas of research has declined by 17% (from 3,207,094 to 2,656,753 procedures) over the same period. Procedures involving transgenic animals now account for 19% of all procedures conducted on animals in UK. Similar pattern on usage of this technology is being contemplated in USA and other developed countries while the developing nations like India are considered as future invest centres for bulk production of pharmaceuticals at low cost to meet the global human requirements. In this chapter we have made an attempt to review all the latest techniques for production of mammalian transgenics especially the farm animals.