A Taiwanese city is keeping dog mess off its streets by offering prizes to owners who clear up after their pets.Officials in New Taipei City say that more than 4,000 people have collected 14,500 bags of excrement. For each bag they turned in, they were given a lottery ticket. A woman in her 50s won the top prize - a gold ingot worth $2,200 (£1,400).The scheme was due to end in October, but officials said it had been so successful it had been extended.The BBC's Cindy Sui in Taipei says that it has been credited with halving the amount of dog mess in the city, which is near the capital.Dog poo is a health hazard because it contains bacteria that can cause severe stomach upsets if ingested, including a roundworm infection called toxocariasis which is especially dangerous to children.As the scheme - which began in August - grew more successful, more prizes were added.On Wednesday some of the winners were picked. The woman who won is among a team of neighbourhood volunteers who already helped to clean up the streets, including by picking up dog mess.Smaller gold ingots, worth several hundred dollars, were given to four other prizewinners. A total of 85 people won prizes, including household appliances.City officials told the BBC they did not know whether the collectors were dog owners who were suddenly motivated by gold to be more responsible or whether they were other citizens who simply wanted to win.Now that the programme has ended, officials say that they hope people will have developed the habit of picking up dog mess.They say the city simply cannot afford to keep exchanging dog poo for gold.