How much does grain impact the dairy quality from a cow?

Someone was asking me about grass fed dairy. Yes, I work on farms, but I work on the machinery and the like. All the farm/animal/growing stuff gets left to people who actually know what they are doing. But I get asked these types of questions all the time...

Getting 100% grass-fed dairy in Canada is quite difficult. From what I can understand, it's fairly difficult to import dairy products into Canada, so getting something from the US or abroad is difficult. Getting grass-fed Canadian dairy is nearly impossible because we don't have grass year-round in many places (Vancouver island maybe?). As a result, the best you can get is having your cows out to pasture as much as possible, then feeding alfalfa as much as you can and supplementing with grain during the winter months. The regulations for organic dairy in some provinces means organic grain but also that cows are made to graze grass as much as possible and grain makes up only 20% of their diet.

SO, this is what I was telling the person who asked this question. But then I was returned with "lol, it's not the same at all!" ... which to me seems ... off? Maybe I'm wrong, perhaps the 20% of grain in the diet does make *that* much of a difference - does anyone know?

From what I gather from their comments, want they actually want is to buy the milk and butter directly from the farms, but I've never encountered that in Canada (you can in Vermont I know). So would that mean it's more a question of small scale operations (buying directly from farm/maker) vs more industrialized operations (organic dairy products sold in health stores). That would make sense to me in terms of taste. I'm also wondering if they want grass-fed raw milk...and if that creates a difference in taste?


I'm simply curious. I don't eat much dairy/ milk much anymore because I'm intolerant. If anyone who's in the know could school me, it would be super appreciated.