A 10,000-head pig farm may also support 7,000 rats, according to an article in Southern Rural News last week. The article is an advertisement for pest control companies disguised as journalism, but it raises another potentially serious problem related to the complex business of raising livestock.
The article suggests that Chinese pig farms lose large volumes of feed to rats. They chew holes in feed bags and eat significant quantities of grain. Moreover, the holes in the bags can promote growth of mold and toxicity in feed that's not eaten by rats.
A representative from a rat control company estimates that a 10,000-head swine farm could be feeding rats 200 kg of grain daily or 73 metric tons a year if each of 7,000 rats eats 20-to-30 grams a day. He warns that rats also chew up pipes, wires and heating equipment.
A more troubling prospect is the potential for rats to spread disease. They carry parasites and their droppings can contaminate feed, fodder, equipment and barns. They can spread 30 kinds of diseases, including major pig diseases like classical swine fever, foot and mouth disease, and pseudorabies.
Of course the article highlights the benefits of hiring pest control companies. A company representative estimates that a large farm could spend 16,000 yuan annually on treatment but losses from rat infestations could be 100,000 yuan. The article also provides some hints for keeping rats under control.
Chinese farms have over 400 million pigs at any given time...and 280 million rats? China has always had rats (they are also a major problem in grasslands); but rats--like pigs--are now being raised on an industrial scale, attracted by the stockpiles of feed. Large farms with deep pockets will take measures to kill them off, but small and medium-size farms probably won't. Another vector for spreading disease that is rarely mentioned.