Enviropig is the trademark for a genetically modified line of Yorkshire pigs with the capability to digest plant phosphorus more efficiently than ordinary unmodified pigs that was developed at the University of Guelph. The benefits of the Enviropig, if commercialized, include reduced feed cost and reduced phosphorus pollution as compared to the raising of ordinary pigs.
Enviropigs create the enzyme phytase in their salivary glands. When cereal grains are consumed, the phytase mixes with feed in the pig’s mouth, and once swallowed, the phytase is active in the acidic environment of the stomach decomposing indigestible phytic acid with the release of phosphate that is readily digested by the pig.
Cereal grains including corn, soybean, and barley contain 50 to 75 percent of their phosphorus in the form of phytic acid. Since the Enviropigs can now digest phytic acid, there isn’t a need to include either a mineral phosphate supplement or commercially produced phytase to balance the diet. Because no phosphorus is added to the diet and there is digestion of the phytic acid, the manure is significantly reduced in phosphorus content, ranging from a 20 to 60 percent decrease depending upon the stage of growth and the diet consumed.
The Enviropig was developed by the introduction of a transgene construct made up of the promoter segment of the murine parotid secretory protein gene and the E. coli phytase gene. This construct was introduced into a fertilized embryo by pronuclear microinjection, and this embryo in addition to other embryos was surgically implanted into the reproductive tract of an estrous synchronized sow. After a 114-day gestation period, the sow farrowed and piglets born were inspected for the presence of the transgene and for phytase enzyme activity in the saliva. Through breeding, this line of pigs is in the 10th generation, and the phytase trait is firmly transmitted in a Mendelian fashion.
About 50 to 75 percent of the phosphorus that is present in cereal grains, corn, and soybeans is present in an indigestible compound called phytate that passes through the pigs digestive tract and is enriched in the manure about 4-fold because the protein and carbohydrates in cereals are digested and absorbed. When manure from ordinary pigs is spread on land in areas of concentrated swine production, there is a build up of phosphorus in the soil. During the spring, run off, or during heavy rain, the phosphorus might leach into ponds, streams, and rivers increasing the phosphorus content, an important nutrient for algae growth. With an excess of phosphorus there is increased algal growth that ultimately causes a reduction in oxygen concentration within the water that results in the death of fish and other aquatic animals. Often times, toxins are produced by the algae and the water is no longer safe to drink. Since the Enviropigs emit less phosphorus in the manure, there is less opportunity for pollution of water sources.
Cathy Holtslander, community organizer with Saskatchewan-based Beyond Factory Farming, says an alternate way to address the issue of phosphorus pollution would be to reduce the concentration of hog-confinement facilities and the numbers of animals within them.
On February 20, 2010, the Department of the Environment of the Canadian Government determined that Enviropig is in compliance with the Canadian Environmental Protection Act and can be created outside of the research context in controlled facilities where they are segregated from the other animals. Steven Liss, associate vice-president of the University of Guelph said in February of 2010 that “Applications to other federal agencies to assess the safety of Enviropigs for human food and animal feed were currently under review both in the U.S. and Canada and there is no set date when or if these reviews will conclude.”
The United States Food and Drug Administration has a Guidance Document that outlines types of data that is needed to assess food and environmental safety of a genetically engineered food animal: 1: product identification/description. 2: molecular characterization of the genetic construct introduced into animal. 3: molecular characterization of the GE animal lineage. 4: phenotypic characterization of the GE animal. 5: stability of the new inheritable trait through generations. 6: food, feed, and environmental safety. 7: effectiveness of the new trait/claim validation. 8: post-approval responsibilities.
Regulatory approval of the Enviropig will be necessary in any country before commercialization of these pigs for human food consumption.
Image Caption: The Large White, also known as the English Large White, is a breed of domestic pig originating in Yorkshire, hence also known as the Yorkshire pig.. Credit: Grimlock/Wikipedia (CC BY-SA 3.0)