NZ Pork told a conference in Auckland on Thursday that one of the major threats to the country's biosecurity is the practice of feeding food waste to backyard pigs.
Chief executive Owen Symmans, told the Agricultural and Horticultural Science, Biosecurity Forum, that pigs are highly susceptible to disease and that feeding food waste to pigs has led to numerous outbreaks of foot and mouth disease abroad.
But he said authorities here have no idea about the scale of the backyard pig industry - and no way to police what they're being fed.
Mr Symmans said there are about 130 commercial herds in New Zealand and the census indicates there are about 7000 New Zealand properties that have got pigs.
He said some of those properties may have only one or two pigs, while others will have considerably more than that and it's a significant risk.
"Nobody knows where they are, who they are and where they market but if you go on TradeMe and have a look at the number of pigs for sale around the countryside, you'll be absolutely surprised."
Mr Symmans said there are a number of places in Auckland that are supplying the underground market.