A Primer on Cloning and Its Use in Livestock Operations
The responses to the questions provided in this document represent the FDA’s view in light of the conclusions and recommendations outlined in the Animal Cloning Risk Assessment, Risk Management Plan, and Guidance for Industry #179.
Imagine the perfect dairy cow. For eight years she has gotten pregnant on the first try, given birth easily, and produced gallon upon gallon of the best milk. Even when others in the herd got sick, she stayed healthy. She is ideally suited to the climate in which she lives. The farmer has depended on this cow and her daughters in lean times to carry the farm through, but now she is at the end of her reproductive life.
Although the farmer may have this cow’s daughters to carry on the line, he also has another alternative: copying her. Biological copying is referred to as cloning. By cloning his prize cow, breeding the clones, and keeping their offspring, the farmer can introduce the natural positive characteristics into the herd quickly. It would take several more years to achieve these same improvements by conventional breeding.
Farmers can also clone animals to produce more uniform quality meat. Take, for example, a male swine (boar) that time after time sires offspring that mature quickly and provide lean meat. If a farmer has several of these boars he could quickly produce an entire herd with consistent, high quality meat.
Researchers have been cloning livestock since 1996. When it became apparent that cloning could become a commercial venture in 2001, the Food and Drug Administration’s Center for Veterinary Medicine asked that food from clones and their offspring be voluntarily kept out of the food chain. FDA then began an intensive evaluation that included examining the safety of food from these animals.
Cloning is a complex process that lets one exactly copy the genetic, or inherited, traits of an animal (the donor). Livestock species that scientists have successfully cloned are cattle, swine, sheep, and goats. Scientists have also cloned mice, rats, rabbits, cats, mules, horses and one dog. Chickens and other poultry have not been cloned.
Most people think of livestock breeding taking place through traditional mating, in which males and females physically get together to reproduce. In fact, this is not often the case. Traditional mating is not that efficient, if the goal is to produce as many offspring as possible. For example, a male has enough sperm to produce many more offspring than would be possible by traditional mating. Traditional mating also has certain risks: one or both of the animals may be injured in the process of mating. The female may be hurt by the male because he is often much larger, or an unwilling female may injure the male. There is also a risk of infection or transmission of venereal disease during traditional mating.
Because of these factors, many farmers use assisted reproductive technologies (ARTs) for breeding. These include artificial insemination, embryo transfer, and in vitro fertilization (a process by which egg and sperm are united outside the body). Artificial insemination was first documented in the breeding of horses in the 14th century. The first successful embryo transfer of a cow was in 1951, and the first in vitro fertilization (IVF)-derived animal was a rabbit born in 1959. Livestock production in the United States now uses all these methods regularly. For example, most dairy farms don’t have bulls, so more than 70 percent of the Holstein cows bred in the United States are artificially inseminated. The frozen semen can come from a bull many miles, or even many states, away.
Cloning is a more advanced form of these assisted reproductive technologies. Much of the public perception of cloning likely comes from science fiction books and movies. Some people incorrectly believe that clones spring forth fully formed, or are grown in test tubes. This is just not the case.
Clones are born just like other animals. They are similar to identical twins, only born at different times. Just as twins share the same DNA, clones have the same genes as the donor animal. A clone is not a mutant, nor is it a weaker version of the original animal.
In all of the other assisted reproductive technologies, the male and female parents each contribute half of their genes to their offspring. Farmers have worked for years to choose animals with the best traits and breed them together. This increases the chance these good traits will be passed on and become more common in livestock herds. Even though farmers have been able to improve their herds over time, they still can’t absolutely predict the characteristics of the offspring, not even their gender. Cloning gives the farmer complete control over the offspring’s inherited traits. Thus, a farmer who clones an especially desirable but aging or injured animal knows in advance that the clone will have the genetic potential to be an especially good, younger animal. He can then use that animal to further reproduce by traditional mating or other ARTs
Most cloning today uses a process called somatic cell nuclear transfer (SCNT). Just as with in vitro fertilization, scientists take an immature egg, or oocytes, from a female animal (often from ovaries obtained at the slaughterhouse). But instead of combining it with sperm, they remove the nucleus (which contains the oocytes’s genes). This leaves behind the other components necessary for the initial stages of embryo development. Scientists then add the nucleus or cell from the donor animal that has the desirable traits the farmer wishes to copy. After a few other steps, the donor nucleus fuses with the ooplast (the oocytes whose nucleus has been removed), and if all goes well, starts dividing, and an embryo begins to form. The embryo is then implanted in the uterus of a surrogate dam (again the same as with in vitro fertilization), which carries it to term. ("Dam" is a term that livestock breeders use to refer to the female parent of an animal). The clone is delivered just like any other baby animal.
There are no complications that are unique to cloning. The problems seen in clones are also seen in animals born from natural mating or ARTs. They seem to happen more often in clones for a number of reasons that probably have to do with parts of the procedure that occur outside the body. The embryo may fail to develop properly during the in vitro stage or early on after transfer to the surrogate and may be flushed out of the uterus. If it does develop, the embryo may not implant properly into the uterus of the surrogate dam. Alternatively, the placenta may not form properly, and the developing animal won’t get the nourishment it needs.
Large Offspring Syndrome (LOS) is seen in pregnancies of cattle and sheep that come from other ARTs and cloning. With LOS, the fetus grows too large in the uterus, making problems for the animal and its surrogate dam. LOS has not been observed in goats and swine.
Most clones that are normal at birth become as strong and healthy as any other young animals. Calf and lamb clones tend to have more health problems at birth, and may be more likely to die right after birth than conventionally bred animals. Clones born with abnormalities may continue to have health problems for the first few months of life, but by the time clones are young adults, it’s not possible to tell them apart from other animals of the same age, even if you conduct a detailed examination. Scientists at FDA and research institutions have looked at extensive health records, the development of clones, and blood work for clones that’s similar to what people get when they have physicals. These results show that the clones are perfectly healthy, and walk, wean, grow, mature, and behave just like conventionally bred animals.
The main use of agricultural clones is to produce breeding stock, not food. Clones allow farmers to upgrade the overall quality of their herds by providing more copies of the best animals in the herd. These animals are then used for conventional breeding, and the sexually reproduced offspring become the food producing animals. These animals are not clones—they’re just like other sexually reproduced animals. Just as farmers wouldn’t use their best conventionally bred breeding animals as sources of food, they are equally unlikely to do so for clones.
Some examples of desirable characteristics in livestock that breeders might want in their herds include the following:
Disease resistance: Sick animals are expensive for farmers. Veterinary bills add up, and unhealthy animals don’t produce as much meat or milk. A herd that is resistant to disease is extremely valuable because it doesn’t lose any production time to illness, and doesn’t cost the farmer extra money for veterinary treatment.
Suitability to Climate: Different types of livestock grow well in different climates. Some of this is natural and some results from selective breeding. For instance, Brahma cattle can cope with the heat and humidity of weather in the southwestern United States, but they often do not produce very high grades of meat. Cloning could allow breeders to select those cattle that can produce high quality meat or milk and thrive in extreme climates and use them to breed more cattle to be used for food production. Similarly, pork production has traditionally been centered in the eastern United States, but is moving to different regions of the United States (e.g., Utah). Cloning could allow breeders to select those swine that naturally do well in the new climate, and use those swine clones to breed more swine to be used for food production.
Quality body type: Farmers naturally want an animal whose body is well suited to its production function. For example, a dairy cow should have a large, well-attached udder so that she can produce lots of milk. She should also be able to carry and deliver calves easily. For animals that produce meat, farmers breed for strong, heavily-muscled, quick-maturing animals that will yield high quality meat in the shortest time possible. The most desirable bulls produce offspring that are relatively small at birth (so that they are easier for the female to carry and deliver) but that grow rapidly and are healthy after birth.
Fertility: Quality dairy cows should be very fertile, as a cow that doesn’t get pregnant and bear calves won’t produce milk. Male fertility is just as important as that of the female. The more sperm he can produce, the more females a bull can inseminate, and the more animals can be born. Beef cattle or other meat-producing animals such as swine need to have high fertility rates in order to replace animals that are sent to slaughter. Cloning allows farmers and breeders to clone those animals with high fertility rates so that they could bear offspring that would also tend to be very fertile.
Market preference: Farmers or ranchers may also want to breed livestock to meet the changing tastes of consumers. These include traits like leanness, tenderness, color, size of various cuts, etc. Preferences also vary by culture, and cloning may help tailor products to the preferences of various international markets and ethnic groups.
How does cloning help get these characteristics into the herd more quickly? As we’ve previously said, cloning allows the breeder to increase the number of breeding animals available to make the actual food production animals. So, if a producer wanted to introduce disease resistance into a herd rapidly, cloning could be used to produce a number of breeding animals that carry the gene for disease resistance, rather than just one. Likewise, if a breeder wants to pass on the genes of a female animal, cloning could result in multiples of that female to breed, rather than just one.
Yes. Food from cattle, swine, and goat clones is as safe to eat as food from any other cattle, swine, or goat. But it’s important to remember that the primary purpose of clones is for breeding, not eating. Dairy, beef, or pork clones make up only a tiny fraction of the total number of food producing animals in the United States. Instead, their offspring would be the animals actually producing meat or milk for the food supply.
Dairy clones will produce milk after they give birth, and the dairy farmers will want to be able to drink that milk or put it in the food supply. Once clones used for breeding meat-producing animals can no longer reproduce, their breeders may also want to be able to put them into the food supply.
In order to determine whether there would be any risk involved in eating meat or milk from clones or their offspring, in 1999 the FDA asked the National Academy of Sciences (NAS) to identify science-based concerns associated with animal biotechnology, including cloning. The NAS gathered an independent group of top, peer-selected scientists from across the country to conduct this study. The scientists delivered their report in the fall of 2002. That report stated that theoretically there were no concerns for the safety of meat or milk from clones. On the other hand, the report expressed a low level of concern due to a lack of information on the clones at that time, and not for any specific scientific reasons. The report also stated that the meat and milk from the offspring of clones posed no unique food safety concerns.
Meanwhile, FDA itself began the most comprehensive examination of the health of livestock clones that has been conducted. The evaluation has taken over five years. This examination formed the basis of a Draft Risk Assessment to determine whether cloning posed a risk to animal health or to humans eating food from clones or their offspring. FDA conducted a thorough search of the scientific literature on clones, and identified hundreds of peer-reviewed scientific journal articles, which it then reviewed. The agency was also able to obtain health records and blood samples from almost all of the cattle clones that have been produced in the United States and data from clones produced in other countries. FDA compared these health records, and the independently analyzed blood results with similar samples from conventional animals of the same age and breed that were raised on the same farms. FDA received thousands of comments from the public in response to the Draft Risk Assessment. For the final version of the Risk Assessment, FDA conducted an up-to-date review of the literature, added additional information from hundreds of additional references, and made many changes to address some of the public comments.
After reviewing all this information, FDA found that it could not distinguish a healthy clone from a healthy conventionally bred animal. All of the blood values, overall health records, and behaviors were in the same range for clones and conventional animals of the same breed raised on the same farms. FDA also observed that milk from dairy clones does not differ significantly in composition from milk from conventionally bred animals.
In the Risk Assessment, FDA concluded that meat and milk from cattle, swine, and goat clones is as safe as food we eat from those species now. Although we don’t have any particular concerns about sheep clones, we did not have enough information to make a decision on the safety of food from sheep clones.
For another study similar to the one conducted on cow clones, the agency also evaluated the health of offspring sexually derived from swine clones, as well as the composition of their meat. After reviewing this very large data set, the agency concluded that all of the blood values, overall health records, and meat composition profiles of the progeny of clones were in the same range as for very closely genetically related conventionally bred swine. Based on these results, other studies from scientific journals, and our understanding of the biological processes involved in cloning, the agency agreed with NAS that food from the sexually reproduced offspring of clones is as safe as food that we eat every day. We reiterate, however, that the sexually reproduced offspring of clones would produce almost all of the food from the overall cloning/breeding process.
FDA’s Risk Assessment includes data collected or published before mid-2007. The FDA will continue to monitor closely the development of clones and their progeny as a source for food as further data become available.
Copies of the Risk Assessment may be requested from the Communications Staff (HFV-12), Center for Veterinary Medicine, Food and Drug Administration, 7519 Standish Place, Rockville, MD 20855, and may be viewed on the Internet.
The National Academy of Sciences (NAS) was signed into being by President Abraham Lincoln on March 3, 1863, at the height of the Civil War. As mandated in its Act of Incorporation, the NAS has, since 1863, served to "investigate, examine, experiment, and report upon any subject of science or art" whenever called upon to do so by any department of the government. Scientific issues would become even more contentious and complex in the years following the war. To keep pace with the growing roles that science and technology would play in public life, the institution that was founded in 1863 eventually expanded to include the National Research Council in 1916, the National Academy of Engineering in 1964, and the Institute of Medicine in 1970. Collectively, the four organizations are known as the National Academies. Since 1863, the nation's leaders have often turned to the National Academies for advice on the scientific and technological issues that frequently pervade policy decisions. The Academies and the Institute are honorific societies that elect new members to their ranks each year. The Institute of Medicine also conducts policy studies on health issues, but the bulk of the institution's science policy and technical work is conducted by its operating arm, the National Research Council, created expressly for this purpose. These non-profit organizations provide a public service by working outside the framework of government to ensure independent advice on matters of science, technology, and medicine. They enlist committees of the nation's top scientists, engineers, and other experts--all of whom volunteer their time to study specific concerns. (From the National Academy of Sciences website.)