The Future of Animal Cloning

Terry Etherton

Animal cloning has generated much public discussion about the need for, and safety of this scientific method. In this Blog I present information that the biotechnology is safe for both animals and consumers. In addition, it provides many benefits which is why so many scientists and livestock producers are excited about the technology being approved by the Food and Drug Administration (FDA). The discovery and development of techniques to propagate animals by nuclear transfer (cloning) offers many important applications to animal agriculture, including reproducing highly desired elite sires and dams. Animals selected for cloning will be of great value because of their increased genetic merit for increased food production, disease resistance, reproductive efficiency, or will be valued because they have been genetically modified to produce organs that can be used for transplantation into humans. Cloned animals (or twins) are often more efficient in their use of feed, and consequently, will produce less waste which will reduce the impact of animal agriculture on the environemtn. In addition, there is great potential to develop cloned animals that produce bioproducts that have important biomedical applications.

What is Cloning?

Cloning, a term originally used primarily in horticulture to describe asexually produced progeny, means to make a copy of an individual or, in cellular and molecular biology, groups of identical cells, and replicas of DNA and other molecules. For example, monozygotic twins are clones. Animal cloning in the late 1980s resulted from the transfer of nuclei from blastomeres of early cleavage-stage embryos into enucleated oocytes. The cloning of the sheep, Dolly, was the result of somatic cell nuclear transfer (SCNT) by Wilmut and colleagues (Wilmut et al., 1997). This was a landmark scientific discovery because it demonstrated that it was possible to clone an animal by removing the nucleus (which contains the genetic information in the form of DNA) from a cell of an adult animal, inserting this into an enucleated oocyte (an egg from which the nucleus has been removed), and then activating the “reconstructed” embryo. The resulting cloned embryos are cultured for a period of time to reach the optimal stage for embryo transfer where they are transplanted into a “mother” animal. Cloning by SCNT transfer requires that the introduced nucleus be reprogrammed by the cytoplasm of the egg and direct development of a new embryo, which is then transferred to a recipient mother for development to term. The resulting offspring will be identical to their siblings and to the original donor animal in terms of their nuclear DNA.

Are There Compositional Changes and Adverse Health Effects of Foods Derived From Cloned Animals?

Historically, equivalence of tissue (food) composition has been an important component of the regulatory process to evaluate food safety. For genetically modified plants and the animal biotechnologies reviewed by the Food and Drug Administration, the evaluation has included comprehensive compositional analyses of plants, tissues, and milk (when appropriate). A committee convened by the National Academies (2004) (of which I was a member) found that a comparable approach for animal products, primarily meat and milk, from cloned animals would be an appropriate, scientifically-based approach to assess compositional equivalence. Implicit to assessing compositional equivalence is that no increased health risk would be expected if the compositional analyses of animal products from cloned and non-cloned animals were substantially equivalent.

There is a long history of assessing the safety of foods introduced into the marketplace. The approach involves an integrated multi-disciplinary approach that incorporates molecular biology, protein chemistry and biochemistry, food chemistry, nutritional sciences, and toxicology. It is important to appreciate that absolute safety is not the objective with respect to any methodology or combination of methodologies used to evaluate complex substances such as food. The standard that has been applied is that the food under evaluation should be as safe as an appropriate counterpart that has a long history of safe use. This comparative evaluation process is the foundation of establishing substantial equivalence of the food being evaluated. It also is important to emphasize that it is the food product itself, rather the biotechnology process used to generate genetically modified animals and cloned animals, that should be the focal point of the evaluation. The primary objective of the safety review is to assess food safety; embedded in this is whether the process might affect the food. In addition, it is important to recognize that a statistically significant difference in one or more compounds in the food evaluated and the appropriate comparator does not necessarily imply an outcome with respect to human health. This must be evaluated on a case-by-case basis as part of the regulatory framework. The National Academies Report found that there is no scientific evidence that cloning is associated with any unintended compositional change(s) that results in an unintended health consequence in humans. Since there is no evidence that food from cloned animals poses any increased health risk to the consumer it can be concluded that food from cloned animals should be approved for consumption.


It is important to appreciate that animal cloning is another example of an assisted breeding technology. Farmers have long used artificial insemination and split embryos to improve the health and quality of their herds. A cloned animal is a genetic twin of the donor animal. Cloning is not a transgenic procedure because there is no change in the orginal genome (genetic information stored as DNA in the nucleus) through addition, deletion or movement of the genes. Decades of research have demonstrated that cloned animals are just as healthy and normal as non-cloned animals.


Safety of Genetically Engineered Foods: Approaches to Assessing Unintended Health Effects. Institute of Medicine and National Research Council of The National Academies. The National Academies Press, Washington, DC. 2004.

Wilmut I, Schnieke AE, McWhir J, Kind AJ, Campbell KH. 1997. Viable offspring, derived from fetal and adult mammalian cells. Nature 385:810-813.

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