Dun's task was to create a new cattle and dairy industry out of largely undeveloped island of Hokkaido.

He settled initially at an intermediary experimental farm in Tokyo, teaching up to seventy students assigned by the government in animal husbandry, veterinary medicine and basic techniques of selective breeding.

Dun also married a Japanese woman, Tsuru, in 1875, which led him to extend his contract in Japan several times, despite difficulties such as the Hokkaidō Colonization Office Scandal of 1881.

Dun is also deemed responsible for initiating government policies to eradicate wolves with strychnine and hunting for bounties, which drove the Hokkaidō wolf to extinction by 1895.

Dun considered resigning but at the end of the year married again, to a woman named Yama Takahira.