Now there are only 3000.
This is a family farm, where they grow maize and wheat, as well as raising cattle. The Christensens bought it in 1982 from Mrs Christensen's parents, and it has been in the family since 1760.
They are survivors in an industry that has been squeezed hard. Dairy farming has come under intense pressure around the world in recent years.
Retail giants have demanded the wholesale price of milk fall in many countries, making it more difficult for smaller producers to make a living. Falling sales in the United States in particular has also had an impact.