Turns out "grass fed milk" isn't just a marketing thing to sell more expensive milk, milk from grass fed cows is actually just plain better, featuring an almost 1:1 ratio of omega-3 to omega-6 (conventional milk, fed with primarily soi beans, has like a 1:3 ratio, the average American diet is already super high in omega-6 and very low in omega-3)
Also my kefir grains just really seem to like grass fed milk, shit just ferments faster and ends up even creamier.