Engineered animals may reduce pork industry's negative impact

Chinese researchers have turned to genetic engineering to develop pigs whose manure is more environmentally friendly than that of their conventional cousins.

A study, published recently in eLife, a science journal based in the United Kingdom, found that genetically modified pigs have an improved ability to digest two key nutrients - nitrogen and phosphorus - in their feed. That means less is released into the environment in the form of pig poop.

China is the world's largest pork producer and consumer, accounting for roughly half the total pork production worldwide, according to China Animal Agriculture Association.

Although pigs account for more than 60 percent of Chinese people's demand for meat, they also exert major environmental pressure. Fecal nitrogen from pig farms accounts for about 20 percent of China's total output of nitrogen pollutants, according to the research team from South China Agricultural University in Guangzhou, Guangdong province.

"Our findings indicate that these pigs can save feed and reduce environmental pollution," said Wu Zhenfang, a team leader at the university. "They're a promising resource for improving feed efficiency and reducing the carbon footprint of the pork industry."

The fecal nitrogen and phosphorus output of the transgenic pigs was reduced by up to 45 percent, and the GM pigs showed a more than 14 percent improvement in their ability to absorb those nutrients.

"Pigs release harmful amounts of these chemicals because they lack the microbial enzymes that break down phytate - the main source of plant-derived phosphorus - and types of dietary fiber called nonstarch polysaccharides, which block the release of nitrogen," said Zhang Xianwei, the lead author of the research paper.

"We suggest that making up for the pigs' deficiency in the three enzymes will benefit the pork industry by increasing the animals' absorption of feed and reducing their nutrient emissions."

In the research, Zhang and his team placed the three enzymes into the pig genome. The enzymes specifically affected the pigs' salivary glands, allowing the digestion of phytate and nonstarch polysaccharides to begin in the mouth, Zhang said.

Wu said the results of the research indeed showed that the pigs were able to digest these and other key nutrients, thereby lowering the amount discharged as waste.

The team also found that the animals' increased nutrient uptake led to a faster growth rate, he said.

Zhang said the team has produced eight healthy genetically modified pigs since the first one was created in 2013, and no negative side effects have been reported.

The animals' mood, behavior, reproductive capacity, blood physiology and natural biochemical processes remained unchanged, he said.

"We have tested edible parts of the pigs, including meat, bone, fat and viscus (liver and kidney), and found their nutrition similar with naturally bred pigs," Zhang said. "The enzymes that were delivered into the genome of the pigs were expressed specifically in their salivary gland, so there is no food safety problem with the meat."

The team applied to the Ministry of Agriculture and Rural Affairs in August for a large-scale trial, and is awaiting a reply.

More research and approval procedures from the ministry are needed before it is possible to produce such pigs on an industrial scale, he said.

Worldwide, the use of genetically modified food plants and animals is strictly controlled.

Currently, the Ministry of Agriculture and Rural Affairs has only approved GM cotton and papaya for commercial production in China. The ministry has said it will give a nod to nonfood GM agricultural products first and grains last.

Although not in commercial use, a number of genetic modifications are in the research phase. A modified carp was successfully developed by the Chinese Academy of Sciences in the 1980s, but still has not gained approval for commercial use.