>>12581025finding data on the market share of grass fed milk is surprisingly difficult if you're not willing to shell out 4000$ to make a point in an internet argument, apparently
all I could find was some eu article about dairy products in general and that "most milk", however much that might be, comes from cows that are fed a mixture of grass silage and grain silage (corn was given as an example, but no specific data there either).
seeing how grass fed is a mark of quality that lets you sell the product at a higher price, unless it says grass fed on the packaging I'd assume that it isn't grass fed.
I'm happy if you buy all your animal products from ethical sources, and I wouldn't really care if you didn't, but the average troglodyte on welfare will not care for grass-fed milk and buy whatever is cheapest.
grinding oats and mixing them with water makes more """milk""" than feeding those oats to a cow and milking it. most of it gets turned into body heat and shit.