Complex sentence: Peak production was reached in the 1970's, when approximately 130,000 skins were produced at the Keppo farm, while the production of all of the Keppo owned farms together were approximately 480,000 mink-and 150,000 fox-skins.
Split into simpler sentences: Peak production was reached in the 1970's, when approximately 130,000 skins were produced at the Keppo farm. The annual production of all of the Keppo owned farms were 480,000 mink-and 150,000 fox-skins.