Other researchers say the mistake might not be with nature, but in the way the pigs are raised. In confinement, pigs are fed grains that are high in phosphorus. But if the pigs are allowed to graze, the amount of grain they eat can be minimal, according to E. Ann Clark , associate professor of plant agriculture at the University of Guelph. Chicken feces also contain phosphorus, but scientists haven't yet figured out how to make a transgenic chicken. Cows don't have the problem because they metabolize the phytate without leaving phosphorus behind.
Farmers now give pigs phytase supplements in their food, but it's expensive and difficult to store.
Forsberg and his colleagues call the genetically altered pig the Enviropig, but critics say if farmers really want to be environmentally friendly, they should let pigs graze on greens instead of feeding them grains. Clark offers Greg Gunthorp , a pig farmer in Indiana, as an example. His pigs get almost all of their sustenance from grazing on greens. The sows get only greens, while the pigs that will be slaughtered get a small amount of grain. Gunthorp says on his website that pasture pigs have far fewer health problems, such as respiratory disease and tail biting.