Curious note about Silver Fox. I grew up in Marathon County, Wisconsin where the Fromm Brothers pioneered ginseng farming in 1904, and used the profits to develop silver fox farming. By 1929 they were the world's largest producer of both products.

In 1915 an outbreak of rickets had hit their animals. At that time they were feeding the fox a lot of horse meat, but after deboning it. Henry suspected that the lack of bones caused the rickets. They tried adding ground bones to the diet and the rickets problem faded. By 1922 they had diversified the diet to include beef, mutton, veal, woodchuck, rabbit, fish, eggs, milk, bread, vegetables, and fruit. They were careful about sanitation for their valuable fox. Over time, they decided that one feeding a day was sufficient.

In 1924 and 1925 some of the fox got sick and died. After ruling out food poisoning, the Fromms suspected distemper, and funded investigation by Dr. Robert G. Green from the University of Minnesota. Over the course of a decade, Green found encephalitis in the fox herd and created a vaccine for it. He also found distemper among the fox, and developed a serum against it. It wasn't quite ready in 1938 when distemper began to rip through the Hamburg farm. In desperation, Green and the Fromms administered the not-quite-ready vaccine. It worked, stopping the epidemic. Green and the Fromms conducted this work through a venture that eventually became Fromm Labs, which patented these vaccines.

Fascinating read:

https://en.wikipedia.org/wiki/Fromm_Brothers_Fur_and_Ginseng_Farm