Disease resistant livestock
Disease resistant livestock are animals that have been selectively bred or genetically modified to increase their tolerance against certain pathogens. This may be desired to increase the productivity of farm animals or to enhance the nutrition of their products. This is projected to be used most in developing countries where disease can obliterate half of a farmer's livestock population every year. The processes to genetically modify livestock remain diverse, including direct gene insertion into an embryo, somatic cell nuclear transfer, and the encouragement of mutations in specific DNA regions. Though the benefits to GMO in this field remain explicit, many still question the ethical validity of such manipulation of nature.
History and Theory
Throughout the world, agriculture remains a chief source of food and consumer goods, ranging from dairy products to clothing. For centuries, the process of selective breeding has allowed humans to prolong desired traits within their cattle population. By selectively breeding muscular bulls with productive cows, for example, the likelihood of producing muscular, productive offspring increases substantially. In addition to undesired traits, however, disease and parasites also present a malicious detriment to the efficiency and sustainability of agricultural industries. This fact is particularly evident in third-world countries, where relatively primitive agricultural methods and numerous insect vectors make these livestock vulnerable to emaciating diseases. In the United States, livestock disease cost over 17% of the annual turnover capital supplied through their products and costs up to 50% in underdeveloped countries.
One common methods to produce resistance toward specific pathogens remains the manipulation of genetic information. A specific species may possess a natural immunity toward a specific disease, and this genetic information may be removed from the original host and introduced to livestock, which may then express these genes themselves. Another method to encourage resistance is the breeding of naturally more tolerant members of a livestock population, which seem to possess increased immunity based on the interaction of various genetic foci and epigenetic factors. A procedure known as gene knockout has also proven successful in decreasing susceptibility to diseases and disorders. A preexisting gene may code for a protein linked with several disorders, and if this organism can survive without this protein, scientists may completely remove this gene. This effectively prevents most complications associated with that specific protein. Scientists must exercise caution as they intentionally alter genetic information, however, from concerns regarding the mutability of bacterial strands to combat these antibodies and the unforeseen effects of the genetic introduction.
Over the past 30 years, several techniques have been developed to manipulate the genes of livestock to resist disease. The first technique, pronuclear microinjection, involved the direct introduction of a specific gene into the zygote of an animal. As the fetus further developed, the gene becomes widely incorporated into the animal's genome and may express itself. This method, although effective in mice test subjects, was inefficient for larger mammals such as cattle and resulted in fewer successful gene expressions. When successful, this method was used primarily to increase muscle growth in cattle and pigs. These changes typically produced negative health effects as well. The second method, developed most successfully in 1996 in sheep, is somatic cell nuclear transfer (SCNT). This process involves artificially injecting a somatic (adult) cell's nucleus into a denucleated egg. This process allows scientists to more effectively determine which genes are expressed and at what point in the organism's life the expression occurs. In a combination of these two methods, random transgene insertions became popular. This involves injecting a particular gene into somatic cells and then using these cells as donors during SCNT.
Throughout the past decade, several similar methods have been developed such as Recombinase-mediated insertions and gene targeting by homologous recombination. Most of these alternative methods involve the use of somatic cell nuclear transfer. A recently developed method known as unspecified, site-specific mutations has allowed scientists to attain genetic manipulation with a high degree of success. In this model, DNA/RNA genome editing nuclei can be inserted into targeted somatic cells. These nuclei induce double strand breaks in specific genetic locations in the somatic cell. Without a repair mechanism in place to properly reconnect these strands in these somatic cells, a biological system known as non-homologous end joining (NHEJ) occurs in the cell. This process is much more prone to error than other DNA repairing systems and often results in mutations, deletions, or insertions. By targeting specific locations for this mutation site, scientists can achieve a desired change up to 50% of the time. In fact this model was used to remove an allergenic protein from cows' milk through deletion. Other methods, including precision mutagenesis, remain in refinement stages and may be used more widely in the future.
Within the past decade, the growing malignancy of mastitis among bovine populations has solicited artificial intervention. Mastitis is a disease that infects the mammary glands of cows. The pathogen enters through the teat and destroys mammary tissue, dramatically lowering the productivity of infected cows. While some populations retain increased resistance to this disease, few breeding technique can completely eradicate these infections. Researchers have successfully introduced genetic splices from foreign organisms into a test group of cows. This insertion provided the mammary epithelium with the ability to manufacture lysostaphin and secrete the antimicrobial peptide into milk. Staphylococcus aureus, one of the most prominent strands associated with mastitis, retains a particular intolerance for lysostaphin. In many cases, this allowed the mammary tissue to render the S. aureus inactive and enables the milk to completely kill the bacteria. Although this method has not yet been perfected or universally accepted, this success has provided credence to the potential benefits of genetically modified cattle.
An additional disease preventable through genetic manipulation is Bovine Spongiform Encephalopathy, commonly referred to as Mad Cow Disease. This neurodegenerative disorder results from complications with the protein prion during manufacturing. Through the process of gene knockout, researchers were able to produce prion-free cattle. These cows were not negatively affected by the procedure, and they remain immune to all forms of Spongiform Encephalopathy.
In aquaculture, transgenic catfish are also showing resistance to harmful diseases. Many common types of aqueous bacteria are harmful toward catfish. After extensive research, scientists have isolated a gene from the moth Hyalophora cecropia that codes for cecropin. This molecule remains effective in killing several types of microbes and bacteria affecting catfish. After insertion of this genetic information, cecropin catfish populations achieve a much lower susceptibility to E. coli than untreated populations.
Social and Moral Implications
As the field of genetic engineering continues to develop for applications in animals, ethical questions present themselves. Many people and even governments have expressed concern for the well-being of animals in genetic engineering experiments and have established systems to monitor this field of technology. This acknowledgment of public opinion remains especially important considering that many experiments in genetic engineering use public funds. Because cloning remains prevalent in the field of disease resistance in livestock populations, many question if mankind is overstepping its bounds by directly selecting and prolonging traits purely to suit his needs. The processes involved in genetically modifying an organism are also generally invasive toward the organism. In addition to many organisms and embryos being sacrificed in the name of scientific research, even living test subjects may undergo tissue surgeries, artificial insemination, castration, or other means to obtain genetic data. Some argue that even the data and products obtained through this research does not justify these methods.
Additionally, an underlying public apprehension to genetically modified foods has stunted the growth of genetic manipulation in farm animals. The common sentiment remains that the more natural a product is, the healthier for one's body the product is long-term. While many common products remain the result of genetic manipulation, the public seems to demote their worth and health benefit as these products are condemned by competitive companies. Similarly, genetically modified pets, such as GloFish, remain a topic of heated debate. Many consider the insertion of foreign DNA for the purpose of amusement to be inhumane while others see little issue in the matter. In fact, the state of California has actually banned GloFish on grounds that this application of advanced human technology should not be encouraged in trivial pursuits. As the use of genetically engineered organisms becomes more widespread in the near future, the ethical debate will intensify, soliciting new policies and standards on agricultural genetics.
Biotechnology has opened fields that could prevent endemic deaths throughout third-world agriculture.
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