CNN) -- Still reeling from news of melamine-tainted eggs and dairy, China launched a massive inspection into animal feed manufacturers -- seizing more than 3,500 tons of tainted feed, state-run media reported Sunday.
Poultry products, including eggs, may be contaminated with melamine through animal feed.
The Agriculture Ministry deployed 369,300 agricultural experts and law enforcement personnel to inspect 250,400 animal feed producers and farms, the Xinhua news agency reported.
Wang Zhicai, the ministry's director of husbandry and livestock, said the inspectors confiscated and destroyed 3,682 tons of melamine-tainted feed, shut down 238 feed producers and investigated 278 other companies and farms suspected of illegal activity, Xinhua reported.
Some 22,700 batches of animal feed were checked for melamine and nearly 98 percent met government standards, Xinhua reported, citing the Agriculture Ministry.
It remains unclear how much tainted feed has entered the food chain.
In the aftermath of the melamine-tainted milk scandal, "there has been a national focus on the discovery of melamine in animal feed and its component ingredients, and there have been particular movements to achieve quality and safety in animal feed," Wang said, according to Xinhua. 
Watch more about the tainted food scandal »
Wang said the ministry issued a rule in June 2007 that banned the use of melamine in feed production, Xinhua reported.
However, the state-run Nanfang Daily published an investigative story last week, saying that adding melamine into animal feed has become an "open secret."
The report said adding melamine into feed started in the aquatic farming industry five years ago, as a way of faking higher protein levels. It then spread into other agro-industries, including poultry. 
Learn more about chemical melamine »
Two years ago, reports revealed pet food exported from China to the United States was spiked with melamine and had sickened and killed dogs.
Several weeks ago, the food scandal spread to milk, biscuits and candies. Then, it was tainted eggs. So far, no illnesses or deaths have been linked to eggs.
Tests in Hong Kong in October showed eggs exported by a Chinese company are contaminated with excessive levels of melamine. In recent days, three other brands of eggs have also been found to contain the chemical.
Ingesting melamine in large doses over an extended period of time could cause kidney stones and other illnesses, though small amounts pose no such danger, agriculture and health experts say.
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As you've probably heard by now, China's been dealing with a massive tainted milk problem. Now that hundreds of tons of milk products have been recalled, precincts are scrambling to figure out what to do with the resulting trash. One city in Southern China has decided that one great way to get rid of all that melamine-laden fluid is to bake them into bricks and cement.
