A total of 22 people have been sentenced to up to eight years in prison for making and selling more than 5,000 kilograms of tainted dog meat, the People's Procuratorate of Rugao in East China's Jiangsu Province announced Tuesday.

Since November 2015, Rugao prosecutors have investigated 14 cases regarding poisoned food, which involved over 5,000 kilograms of poisoned dog meat, 11,000 poisoned birds and 500 kilograms of hazardous chemicals.

Rugao police nabbed Lao Gan (pseudonym) in November 2015 for purchasing 7,000 kilograms of poisoned dog meat before tracking down another five people who bought half of the meat and sold it to restaurants in the outskirts of cities in Anhui, Shandong and Jiangsu provinces. Local police also caught eight men for killing and selling over 11,000 poisoned birds, most of which were sold to restaurants in Shanghai, Zhejiang and Guangdong provinces.

Any tainted meat should be kept away from people's tables to ensure food safety, but there are some loopholes in the supervision of the origins of the food served in some restaurants, Fan Zhihong, a professor at the School of Food Science and Nutritional Engineering at China Agricultural University, told the Global Times.

The People's Procuratorate of Rugao also said on its official website that it is difficult for authorities to identify tainted meat cases because food safety supervision bureaus usually only perform small spot checks on restaurants and few consumers are willing to file reports.

Fan said that unlike pork, beef and mutton, which typically come from large-scale farming, most dog meat comes from unknown sources, and ill-intentioned people may inject chemicals into the meat to preserve it during transportation.

 According to Sichuan-based Boai Animal Protection Center, China's lack of strict quarantine and inspection of the dog meat production chain contributes to many consumers' refusal to eat dog meat.