March 09, 2012

The future of hunger: Part 3

oxenBy Madeline McCurry-Schmidt
ASAS Scientific Communications Associate

The future of hunger: How animal science supports global food security

In Part 2 of “The future of hunger” we looked at how animal scientists use new nutrition research and technology to increase feed efficiency. The more meat, milk and eggs that animals produce for human consumption, the closer we are toward feeding the growing population. In Part 3, we look at how animal scientists can increase food production through animal breeding and biotechnology.

We know very little about the first human to keep a wild ox in a pen. Whoever that person was, he lived in an area of the Middle East called the Fertile Crescent about 10,000 years ago. This discovery, that humans could manage wild animals, helped make early human civilization possible. People could settle into cities and learn new trades thanks to the steady source of food from nearby pastures.

Once humans realized they could domesticate animals like wild oxen or goats, they began managing animals on a genetic level. Even without scientific knowledge of genes and inheritance, it made sense to breed together the best males and females in a herd.

“It is not clear which genes were the first ones to be selected, but those related to behavior must have been subject to early selection pressure. The wild ox was a fearsome beast and docility must have been a very desirable trait,” said Dan Bradley, a professor of molecular population genetics at Trinity College Dublin.    

Bradley studies DNA from ancient animals, like the first domesticated oxen, to see how humans influenced animal genetics over time. Bradley is especially interested in mitochondrial DNA, which is passed through the maternal line in animals.

By studying mitochondrial DNA, Bradley has discovered that European cattle and zebu cattle, two types of common domesticated cattle, came from separate wild populations thousands of years ago. He has also found that mitochondrial DNA is not very diverse in populations of Near Eastern, European and African cattle breeds, suggesting that relatively few wild females served as the foundation of modern cattle breeds.

“It gives a particular perspective; a sort of postcard from the past,” Bradley said.

Over thousands of years, humans have used selective breeding to domesticate the animals that feed the world. Genetic selection has led to larger pigs and more docile cattle, cows that make more milk and chickens with more meat on their breasts. Ask a child to draw a cow, and that cow will not be a wild ox, it will be a black and white splotchy animal not found in the wild.

Genetic selection continues today. Tools for genetic sequencing can make animals more productive. Advances in biotechnology have allowed scientists to create faster-growing fish and more environmentally friendly pigs through genetic modification. Animal genetics has helped feed the world for the last 10,000 years, and new research into animal genetics could help feed the growing population.

Breaking the code

In animal breeding, there is a lot talk about potential. Pick out animals with the right traits, breed them together, and you are, potentially, breeding for better offspring. But with modern genetic sequencing tools, scientists can look beyond the potential benefits of breeding and pinpoint the exact genes responsible for certain traits.

“We are reading the DNA of the animals to know which are best for selection,” said Andre Eggen, a genomics researcher with Illumina Inc., a company that provides tools for genetic analysis.

With genetic sequencing, scientists take DNA and break it into units called base pairs. The order of base pairs is passed down through generations, and they instruct cells to make proteins for traits like hair color and body size. There are natural genetic variations in animal herds, and scientists can compare those variations in base pairs to differences in traits of animals, like fertility, and determine which base pair sequences cause which traits.

In a paper for the magazine Animal Frontiers, Eggen wrote that genomic selection has an advantage over traditional selection. Traditional breeding relies on observation of traits, which can limit accuracy. It is easy to see if one animal is bigger than another, but some traits are less obvious.

“Such difficult-to-measure traits are often critically important,” Eggen wrote. “They include fertility, longevity, feed efficiency and disease resistance.”

In an interview, Eggen said scientists have had success in using genetic selection to breed better cattle.

“We can screen the population, and then we can start selecting from those for meat quality,” said Eggen.

Genomic selection has already increased productivity in the dairy industry. Dairy cows are bred for high milk yield, and it is easier to measure genetic potential for high yield in a female cow: just measure the milk. But selecting a bull is more difficult. Bulls do not make milk, so breeders have to wait for a bull to have daughters and then measure milk production from those daughters. This process, called progeny testing, can be effective, but it also means time and food can be used on unproductive bulls. With genetic analysis, all that could change.

“Genomic selection gives AI [artificial insemination] companies the ability to carry out accurate selection decisions at a young age by using DNA testing,” wrote scientist Jonathan Schefers, from Alta Genetic USA, and scientist Kent Weigel, from the University of Wisconsin-Madision, in an Animal Frontiers paper.

According to Schefers and Weigel, more than 90 percent of bulls in certain dairy breeds have been DNA tested. They believe that as scientists and producers test more and more animals, predictions for offspring milk yield will be even more accurate. With accurate predictions, producers can cut down the time between generations and breed productive cows more quickly.

“Many breeders have embraced genomic selection and routinely use GEBV [genomic estimated breeding values] when purchasing semen or deciding which cows and heifers merit investment,” wrote Schefers and Weigel.

The poultry industry is structured differently than the dairy or beef industry. Janet Fulton, a molecular biologist at Hy-Line International, a breeding company for the egg-laying chicken industry, explained that the value of a single male chicken is not as high as that of a bull, but the cost of genetic analysis for one individual is the same. This make recovering the costs of genetic analysis trickier. Instead of buying semen from a valuable bull and inseminating a herd of cows, poultry producers buy “commercial chicks.” Commercial chicks are bred from four “pure lines” of chickens chosen for valuable traits.

Poultry breeders base decisions on the observable, or phenotypic, traits. In the egg-laying hen industry, breeders consider traits like egg size and feed efficiency when breeding chickens. Fulton said genomics tools are used together with this traditional quantitative selection breeding program.  For example, some chickens inherit genes that make them produce eggs with a fishy odor. Through the use of comparative genomics, scientists identified the genetic mutation that causes fishy odor. Several breeding companies have now eliminated this defect from their lines.

Fulton believes genetic analysis could also keep chickens healthier, not only by selecting for disease resistance in the birds themselves, but by analyzing the microbes inside of them. Chickens, like humans, live with a beneficial population of gut microbes. With genetic analysis, said Fulton, scientists could identify the microbes in chickens and promote the growth of microbes that aid digestion.

“It could have a great influence on feed efficiency,” Fulton said.

The tools for genetic sequencing and analysis have become less expensive as technology has improved and scientists have sequenced more animals. Fulton thinks genomics could go even further.

“We know there’s a difference from one line to the next. The question we’re trying to answer is: what genes are different?” Fulton said. “How do all the genes interact together? How do proteins fold together? No one really knows that yet.”

Genetic sequencing is a high-tech tool, but Eggen said it is a natural step forward if scientists and the animal agriculture industry want to produce more food.

“It is just an extension of what we have been doing for centuries,” Eggen said.

Tweaking the code

Research into genetic selection can make it sound like DNA is law; whether an animal is big or small, sickly or healthy depends on genes. But new research shows that DNA is flexible, and environmental pressures can influence gene expression. The emerging field of epigenetics, or “fetal programming,” could help the animal industry raise healthier animals and produce more food.

To understand how epigenetics works, it is important to understand that organisms have a very large array of genes and not all these genes are expressed. Research shows that animals begin adapting to the environment while still in the womb. Epigenetic research is important because it shows that environmental pressures, like disease or nutrition, can trigger the expression of certain genes and affect efficiency in animal production.

Even in the warmth of the womb, fetuses can be harmed by exposure to chemicals or maternal malnutrition. The DNA of a growing fetus is meant to adapt, so it takes cues from the outside environment. If the mother is undernourished, for example, the fetus is “programmed” to go into a world where food is scarce.

“This research was started in humans, but there was no reason to think that it wouldn’t affect other species,” said Steve Ford, professor of animal science and Director of the Center for the Study of Fetal Programming at the University of Wyoming.

Ford studies how pregnant sheep react to changes in nutrition. He wants to see if maternal nutrition will affect their offspring later in life. Ford said there is a common misconception among farmers that fetuses are too small to demand additional nutrition early in development.

“People tend to under-nourish their females, be that sheep or cattle, during early gestation,” said Ford.

He said that producers tend to only increase maternal nutrition later in gestation, but this is a big mistake. Calves and lambs fattened up during late gestation weigh a normal amount, but their organs and muscles will be underdeveloped because of undernutrition early on. Ford has found that undernutrition in the womb leads to the underdevelopment of the structures that filter blood in the kidneys. These underdeveloped animals look the same as their fully-developed counterparts, but their behavior and organ function is very different.

“Even with the same genetics, two animals can express different phenotypes,” said Ford.

Ford said underdeveloped cattle are “programmed” in the womb to behave as though food is scarce, and they have unstoppable appetites throughout life. Underdeveloped cattle gain weight, but it goes to fat deposits, not muscle. Less muscle on the animal means less meat harvested for human dinner tables.

Ford said he sees similar effects when he over-feeds gestating animals. Again, the offspring are born with huge appetites but do not gain weight efficiently. This behavior and growth is regulated through epigenetics. Under or over-nutrition in the womb prompted the expression of genes for fat deposition and poorer feed efficiency. Epigenetic changes are a way to influence an animal’s genes without changing the actual DNA sequence.

Even though an animal’s genotype appears normal, Ford has found that animals programmed in the womb to express certain genes can pass those traits on to the next generation. In one trial, Ford took underdeveloped sheep from a previous trial and fed them 100 percent of their required diet, an amount which did not promote obesity. He then studied the changes in their offspring. Like their parents, the offspring showed differences in appetite and body fat.

By understanding the role of maternal nutrition, Ford hopes farmers can adjust how they feed their animals. Animals with proper maternal nutrition have normal appetites, meaning farmers can conserve animal feed. The healthy animals then produce more meat using less feed.

With epigenetics, scientists can tweak animal genetics and produce more food for the world.

The biotechnology boom

In 1999, a very special pig was born.

At the University of Guelph, a traditional Yorkshire sow gave birth to the first “Enviropig.” The Enviropig was created by splicing mouse DNA and E. coli DNA into the pig genome. The Enviropig looked exactly like a normal pig, but its new genes made it better at digesting phosphorus.

The genetically modified Enviropig was a solution to a big problem: how to raise enough food to feed the world without damaging the environment. Grain fed to pigs contains large amounts of phosphorus, but the pig digestive system cannot digest all that phosphorus. As a result, pig manure contains excess phosphorus that can run into fresh water, kill wildlife and contaminate the human water supply. To reduce phosphorus in pig manure, many producers buy supplemental phytase, an enzyme that breaks down phosphorus, and add it to their pig feed.

But in the 1990’s, University of Guelph scientist Cecil Forsberg thought there might be a better way. Forsberg studied the physiology of microbes living in ruminant animals like cattle. He noticed that the microbes helped cattle better digest grain.

“We came up with the idea of converting a pig into a cow—in other words, helping it digest cellulose,” said Forsberg in an interview.

The cellulose project did not work out, but it inspired Forsberg to look into phosphorus digestion. The goal was to engineer a pig that could naturally produce the enzyme phytase in its saliva.

“As a consequence, the phosphorus in manure is decreased,” Forsberg said.

The project worked, and the first Enviropig was born. Forsberg found that the genes for better phosphorus digestion were passed down to the pig’s offspring. Today, the University of Guelph works with the tenth generation of Enviropigs. Through genetic modification, Forsberg created an animal that could help farmers increase food production without increasing the environmental impact.

enviropig

The science behind genetic modification, or “genetic engineering,” falls into a broader field called biotechnology. Scientists working in biotechnology apply new technologies, like gene-splicing, to living organisms to create new products. Biotechnology has led to new vaccines, a steady source of antibiotics and even treatments for diseases like diabetes.

Many animal scientists think biotechnology can increase global food production while increasing food safety and decreasing environmental impact.

“Genetically engineered animals have the potential to produce food more efficiently,” said researcher Allison Van Eenennaam.

Van Eenennaam has worked in the field of biotechnology for many years. She began researching cattle cloning even before the birth of Dolly the Sheep. Today, she works as an extension specialist at University of California, Davis. In a guest lecture last year at Oregon State University, Van Eenennaam highlighted the benefits of genetically modified animals like the Enviropig.

Van Eenennaam explained how engineering chickens that do not transmit avian influenza could save human lives. When avian influenza hits a poultry farm, the disease can wipe out flocks. Farmers often kill potentially healthy birds just to stop the spread of disease. And avian influenza is not just a threat to the food supply, it is a huge risk for human health. In 1918, more than 20 million people died during an influenza outbreak that started with transmission from birds to human.

“That was in the days when we had very little air travel and very little international commerce,” said Van Eenennaam.

A disease like the 1918 avian flu virus would probably spread faster today, but geneticists have found a way to stop it. Last year, a team of scientists from Scotland and England reported that they had genetically engineered chickens that could not transmit avian flu.

Genetic modification for disease resistance could expand beyond chickens.

“You could modify pigs so they could become resistant to swine influenza,” said Forsberg.

Van Eenennaam also discussed the creation of the AquAdvantage salmon by biotechnology company AquaBounty. The AquAdvantage salmon has genes from two other fish species, and this combination allows it to grow to market size in one-half the time of conventional salmon. Through genetic modification, scientists have increased feed efficiency.

Scientists have used genetic modification to create healthy, productive animals. Yet, after years of research, these animals are far from our dinner plates.

The ethical obstacle

At the outset of a worldwide population boom, animal producers are applying genetic sequencing and epigenetic research to their herds. These products are seen in our grocery stores and widely accepted by the public.

Biotechnology has not had the same success. Despite years of research, there are no genetically modified animals available for human consumption. Though products like the AquAdvantage salmon are proven safe for human consumption, some people have ethical and environmental concerns. Scientists in the field of biotechnology could help feed the world, yet they have struggled for public and legislative acceptable of their products.

“While science has shown we can do it, society is unsure if we should,” said Van Eenennaam.

Forsberg said he tried, early on, to get the Enviropig approved by the FDA.

“Though we have submitted it for regulatory approval in the United States, we are only partway through the process and it is not approved,” said Forsberg.

Without approval, the scientists can raise the pig, but no one can eat it. Forsberg said the lack of approval is not a matter of food safety.

“Based on extensive chemical analysis, there seems to be no difference between the Enviropig pork and pork from a traditional pig,” Forsberg said.

Misinformation also fuels debates over the environmental impact of genetically modified animals. For example, some argue that if AquAdvantage salmon were to escape into the ocean, they would compete for food with smaller wild salmon, potentially driving the smaller salmon to extinction. But scientists have considered these risks. AquaBounty, the company producing AquAdvantage salmon has engineered the population to be all female and incapable of breeding. The company also plans to raise salmon in inland tanks so they cannot escape into the wild—if they are ever approved for consumption, that is.

The public perception of biotechnology is frustrating for many animal scientists. Van Eenennaam said worries over and genetic modification have left AquAdvantage salmon to languish in FDA review.

“There’s no science-based reason why we should prohibit this technology,” said Van Eenennaam in an interview.

Part of the problem, Van Eenennaam said, is how genetically modified animals are represented. For example, the GE AquAdvantage salmon is nicknamed the “Frankenfish.” During her lecture at Oregon State University, Van Eenennaam showed a slide of a photo she found when Googling “AquAdvantage salmon.” The slide was a Photoshopped image of Frankenstein’s monster combined with a dolphin.

“How can you have a rational discussion after calling something ‘Frankenfish’?” asked Van Eenennaam.

Forsberg said he thinks the public perception problem will fade as the world population increases. At a recent conference in Argentina, Forsberg got a chance to talk with scientists, sociologists and ethicists from around the world. He said speakers from heavily populated countries like China seemed to embrace the idea of genetically modified animals.

“In those countries where there are hungry people, there is less concern about transfer of genes between species,” said Forsberg.

In her lecture, Van Eeneenaan explained that genetic modification is not some huge revolution. Since the early days of human civilization, we have produced animals through genetic selection. Genetic modification is just the newest tool.

Next:

How can new technology and medicine keep animals healthy and increase the world’s food supply? Read part 4 to find out.

References

Animal Frontiers http://animalfrontiers.fass.org/content/current

Enviropig http://www.uoguelph.ca/enviropig/

Forget “Frankenfish.” UC Davis scientist explains the real benefits of genetically engineered animals http://takingstock.asas.org/?p=2408