"Pigs, like the above insects, will eat the feces of herbivores that leave a significant amount of semi-digested matter. In certain cultures, it was common for poor families to collect horse feces as a dietary supplement for their pigs.
Pigs are also known to eat their own feces. However, domesticated pigs should not be allowed to eat any excrement, as this
contributes to the risk of parasite infection. Perhaps for reasons associated with pigs' ready coprophagy (eating faeces), pork was scripturally banned as human food first in the Old Testament and then the Qur'an. Practicing Jews, Seventh Day Adventists and Muslims familiar with this behavior by pigs may cite it as an additional important reason why pork shouldn't be eaten."
From :
http://en.wikipedia.org/wiki/Coprophagia
God didn't change his mind when it came to Christians. Jesus (peace be upon him) came not to destroy the law but to fulfil.
God allowed pure things to be eaten. How a faeces eating animal can be pure is beyond me...
It doesn't matter how cleanly pigs are kept nowadays, thats the innate nature of a pig left to it's own devices.