Gene-based Technologies for Livestock Industries in the 3rd Millennium

Abstract

The first complete genome sequence of an organism was for yeast, in 1996. Since then, the much larger task of doing a complete human sequence has been completed. Those of major domestic animals are following rapidly. It will always be impossible to foresee the full potential of such an explosion in knowledge, but aspects of gene-based technologies are already beginning to have an impact in the livestock sector. The first and most obvious area of impact concerns feed supply, which constitutes 50-75 percent of total costs in many livestock systems. Production costs for maize and soybean are being reduced by genetic modification of the crop for herbicide and insect resistance. Maize has been modified to reduce phosphorous and nitrogen excretion in swine and poultry, and also to provide a more valuable amino acid balance. Genetic modification of the animal is also possible. Most dramatically, the insertion of a growth hormone in the DNA of fish accelerates growth. However, in this and all other cases, the genetic modification (GM) of animals has produced profound physiological disturbances. At the same time, the administration of GM-produced growth hormone to dairy cows is now routine in the United States of America and several other countries. This is not permitted in Europe, where the attitude to all GM technologies has been much more cautious. Conventional selection programmes continue to deliver steady genetic improvement in all animal populations. New molecular methods offer the prospect of enhancing genetic gains, particularly for traits that are difficult or expensive to measure, or which have low heritability. Gene technologies have much to contribute to the control of disease in animals. As pressure to reduce antibiotic and drug use increases, genetically modified vaccines with proven specificity and distinguishable from natural infections are already in use. DNA typing is helping with rapid and precise diagnosis. In addition, the interaction of some pathogens (e.g. scrapie) with the genotype of the animal calls for the application of DNA technologies. Following the BSE epidemic in Europe, safety of livestock-derived foods is high on research and regulatory agendas. DNA techniques are already in use for tracking of sources of Salmonella enterica and Escherichia coli outbreaks, as well as for traceability of product in the food chain.