Environmental issues, including waste management, are the number-one concern of livestock and poultry producers.
As the size and intensity of swine and poultry production operations have increased, so has the amount of manure produced, often with limited land area available for manure application, says E.T. Kornegay, professor of animal and poultry science. “This can lead to a build-up of nutrients in and on the soil with the potential for runoff into waterways.”
Excess environmental phosphorus is suspected as a contributing factor in water-quality degradation and even in the bloom of Pfiesteria piscicida, which has caused fish kills in North Carolina and in tributaries to the Chesapeake Bay.
Virginia Tech animal and poultry science researchers, led by Kornegay, have developed feeding regimens for swine and poultry that result in massive reductions of phosphorus and other nutrients in manure. Kornegay’s recommendations are being used nationwide, and he lectures about his research worldwide.
The key is what Kornegay calls “a miracle enzyme,” microbial phytase.
In Virginia, the state is working with livestock producers to share the cost of the technology needed to apply the phytase to livestock feed on a wide scale.
Until now, producers were adding inorganic phosphorus to livestock diets because pigs and poultry cannot absorb the two-thirds of the phosphorus stored as phytic acid in such plants as corn and soybeans, used as livestock feed. “A portion of the added phosphates and all of the phytic-acid phosphorus are excreted,” explains Kornegay.
Feeding microbial phytase frees a significant portion of the naturally occurring but chemically-bound phosphorus so that it can meet the animals’ nutrition needs.
“Phytase has been around a long time, but it was too expensive to be used routinely,” Kornegay says. That changed in this decade when bacteria were genetically engineered to produce more of the critical enzyme.
Poultry studies in the 1960s demonstrated that feeding fungal phytase increased phosphorus digestion. A commercial phytase was developed by the Dutch company Gist-brocades because of that country’s environmental concerns. With the promise of more plentiful supplies, university and government labs worldwide began to look at phytase as a feed additive, particularly for swine.
“Virginia Tech’s animal scientists were among those who began to study phytase in the early 1990s, when it was decided to use some of the John Lee Pratt endowment to look at ways to protect the environment by reducing nutrient excretion through feeding and ... improved nutrient utilization,”says Kornegay.
More than 30 broiler, turkey, and pig studies conducted at Virginia Tech have demonstrated the effectiveness of adding the genetically engineered microbial phytase to feed to reduce the excretion of phosphorus, as well as some nitrogen, zinc, and calcium. “Although pigs and poultry cannot be made 100 percent efficient in the utilization of nutrients, applying microbial phytase to feed can reduce the excretion of phosphorus by 25 to 40 percent and nitrogen by about 10 percent,” reports Kornegay, who was principal investigator on much of the research.
“We developed response curves to determine what level of additive is the most effective and the most economical in turkeys, broilers, and pigs. We’ve helped move the technology to the application stage.” He says that Virginia is the first state to form a partnership with livestock producers to implement the feeding of phytase.
In 1997, Russ Perkinson, a nutrient management specialist with the Department of Conservation and Recreation, recommended that poultry and pig producers apply for cost-sharing state funds. The department used money appropriated for water quality to share the cost of the equipment to spray phytase on feed pellets, and to fund other initiatives. For example, Kornegay is now working with the industry to develop good monitoring techniques.
The Virginia Tech researchers have also determined the amounts of calcium and zinc that can be freed with a given amount of phytase, so that calcium and zinc additives can also be reduced.
Kornegay credits the Pratt endowment for enabling university researchers to make significant advances in understanding the characteristics of phytase and how it works. “By funding student research on animal nutrition, it was possible for Scott Radcliffe to spend five months in the Netherlands in the spring of 1995 working with the Dutch scientist Age Jongbloed. Scott is now a Ph.D. student.”
The endowment is also paying for cannulation of pigs. A small tube with a removable plug is implanted in the animal, allowing researchers to sample the amino acids present at the end of the small intestine before the contents have been influenced by the microflora in the large intestine. The Virginia Tech researchers have discovered that the engineered enzyme improves amino acid digestion and thus improves protein availability and reduces nitrogen excretion.
Researchers are now looking at the effect of adding phytase to rations that contain different ingredients to study amino acid and energy use in pigs and broilers. “The magnitude of improvement — in terms of nutrients released from feed ingredients — is not likely to be as much as with phosphorus,”says Kornegay, “but Velamuru Ravindran, who earned his Ph.D. at Virginia Tech and is now working at the University of Sydney in Australia, has shown that phytase frees starch as a nutrient — which is an energy source.” While animal scientists are working with livestock producers to apply phytase to feed, Virginia Tech plant physiologist Elizabeth Grabau and her research team are inserting phytase genes into the DNA of transgenic soybean plants. “We are modifying a fungal phytase gene for expression in soybean seeds,” she says.
The researchers introduce phytase genes into soybean by microprojectile bombardment with a gene gun. “We have constructed a gene gun to introduce DNA into soybean tissue culture and have optimized parameters affecting DNA delivery,” Grabau reports.
Her team has demonstrated the ability to regenerate soybeans from immature embryos or embryogenic culture in the laboratory and have compared the processes in different soybean cultivars specifically adapted to growth in Virginia. And, in a collaborative project with Agracetus, Inc., the researchers have tested the effectiveness of transgenic soybeans in poultry feed. Research results, published in Poultry Science, show that “plant-derived phytase provided the same excellent results (as the feed additive) at increasing phosphorus utilization,” reports Grabau.
In addition, she is exploring alternative approaches to lowering phytic acid content by blocking its production. “Just as the USDA has produced and patented a low phytic-acid corn, we are working to produce low phytic-acid soybeans,” Grabau explains.
Meanwhile, the U.S. Egg and Poultry Association is funding research by soil science professor and eminent scholar Lucian Zelazny on the effect of phytase on the form of phosphorus in manure — its solubility and availability as a soil nutrient.
A new area of research is the economic implications. Kornegay is certain that the cost of the phytase is just about offset by the savings in the cost of phosphorus that no longer has to be added to feed. “Furthermore, producers with a limit on the amount of phosphorus that can be applied on their land, save the cost of phosphorus disposal.” He is working with Darrell Bosch, associate professor in applied and agricultural economics, to determine the economic value of reducing phosphorus in feed and manure.
“The bottom line is that improving animals’ digestive efficiency, especially of certain nutrients, reduces excretion,” Kornegay says. Livestock producers can save money and reduce the nutrient load in watersheds of the Chesapeake Bay and other critical waters.