The enzyme is reasonably stable and fully active in the stomach, but is degraded in the small intestine, preventing excretion from the pig.
Lecture 15 Case Study [7,8]: Enviropigs In 2001, researchers at the University of Guelph in Canada developed transgenic lines of Yorkshire pigs that uses cereal feed phosphorus more efficiently which they trademarked EnviropigTM. Enviropig produces the enzyme phytase in the salivary glands that is secreted in the saliva. The enzyme acts in the stomach in the same way as fungal phytase, except it is synthesized in larger quantities in the salivary glands than the amount commonly added to the diet. Ontario Pork, a trade association representing pig farmers in the Canadian province, calls Enviropig "the biggest break-through in pig farming since the invention of the trough." 
Lecture 15 Case Study [7,8]: Enviropigs Enviropigs excrete as much as 60% less phosphorus in the manure as compared to conventional pigs when fed a diet not containing supplemental phosphorus, producing a fertilizer with a higher ratio of nitrogen to phosphorus, which is better suited for long-term repetitive application to agricultural land. Enviropigs utilize practically all phosphorus present in the diet and do not require supplemental phosphate for growth, with a cost benefit of not needing supplemental phosphorus or phytase. It is also more efficient than added supplemental phytase, and utilize dietary trace minerals, proteins and starch more efficiently since phytate complexes them and prevents their absorption in usual pigs.
Lecture 15 Case Study [7,8]: Enviropigs In less developed countries with limited $ to purchase either phosphorus or phytase, the Enviropig would offer a unique advantage, and anyone with experience at raising pigs could raise Enviropigs without any further training. "The environmental barriers are the largest in terms of growing as an industry," says Clare Schlegel, chairman of Ontario Pork, which represents 4,400 hog farmers in the province and has been a primary funder of the Enviropig research. "[Pork producers] are being looked at as polluters -- this is one technology to show that we do care."
Lecture 15 Case Study [7,8]: Enviropigs The Sierra Club, which has made lobbying for controls on pig manure pollution a centerpiece of its clean water campaign, calls the Enviropig a load of hogwash. "This is just another quick fix," says Laurel Hopwood, chair of Sierra Club's genetic engineering committee. "The way to reconcile [the problem] is to stop factory farming." Opponents argue that pork farmers will simply increase the density of pigs on a farm. But for virtually all major environmental groups, the matter boils down to the fact that they oppose the introduction of genetically-engineered organisms into the environment.
Lecture 15 5Rs of Enviropigs Lets consider the expansion of animals with moral worth to the moral worth of animals, people, environment, and reconsider the 5Rs Replacement: Reduction: Refinement: Relevance: Redundancy:
Lecture 15 5Rs of Enviropigs Replacement: Pigs are the relevant species!