The new methods quickly yielded promising results; within two years the overall birth rate for the farm's 6,000 to 8,000 sows rose by 1 percentage point and the mortality rate fell by the same number. In addition, the culling rate for unproductive sows fell by 3 to 5 percent during the same period.

In 2015, an international NGO called World Animal Protection contacted Yao and expressed interest in his attempts to modernize pig rearing in China. The organization also offered to help him improve conditions for livestock on the farm and provided him with an introduction to the concept of ethical treatment of animals.

A gentler approach

Zhao Zhonghua, China country director of World Animal Protection, which has been promoting its aims in the country since 2007, said: "Animal welfare has been promoted in many Western countries for decades. On farms, for example, people are working on issues, including cage-free farming, humane slaughter, live exports and resources for governments, to move towards kinder farming methods."

China's pork industry is one of the biggest in the world, with 688 million animals slaughtered last year, according to statistics from the Ministry of Agriculture and Rural Affairs.

Pigs became World Animal Protection's point of focus as it sought to introduce changes that would benefit a range of animals, such as ducks, chickens and cattle.