Aside from the dizzying stench, hog farms pollute the environment by releasing phosphorous, which leads to the death of fish. Part of the problem is that swine can't digest the phosphorous in barnyard food, so most of it ends up in the farms' effluent. And even more phosphorous is released when manure is used as fertilizer for growing plants. Now researchers have genetically engineered pigs so that they can use the phosphorous in their feed.
A staggering 90,000 tons of phosphorous are released into the environment from animal manure worldwide each year, a 10-fold increase over 50 years ago. Washed away from farms, the phosphorous builds up in lakes, where it causes algae populations to bloom, creating an oxygen shortage that kills fish and disrupts food webs. The kind of phosphorous found in pig chow goes right through pigs because they lack an enzyme called phytase. They need phosphorous to survive, though, so farmers have to buy expensive dietary supplements containing a digestible form of phosphorous, or feed the pigs even more expensive phytase supplements.
So microbiologist Cecil Fosberg at the University of Guelph, Ontario, and his colleagues developed pigs that produce phytase in their saliva. They injected DNA coding for a bacterial phytase gene into more than 4000 pig embryos, 1% of which incorporated the gene. When fed a standard soybean diet, the transgenic pigs excreted up to 75% less phosphorous than control animals, the researchers report in the August issue of Nature Biotechnology. The animals produced less phytase as they got older, but even at market weight, they made enough of the enzyme to get by without supplements of digestible phosphorous. The researchers have established breeding lines of the transgenic pigs and expect to start the food safety approval process shortly.
Cornell University animal scientist Xingen Lei says the findings make a "significant" contribution to the quest for environmentally friendly livestock. He predicts that farms across the globe will rear transgenic phytase-producing pigs within 10 years.