Higher Milk Subsidies for Farmers outside of Wisconsin?

My friend told me there is a 100 year old law where the further a dairy farm is from Wisconsin, the more the farmers are paid (presumably, government subsidies?). It was to encourage milk production originally but my friend was saying its still in place. Can anyone give a wikipedia link or some more information regarding this? Seems like a pretty big thing but I can't find any information on it. Thanks,