I just bought some Kerrygold, It lists grass fed on the packaging. I looked at some other brands but think they are only from animals not treated with Antibiotics and other organic husbandry practices. I don't think not grain feeding is one of them.
You could look at the diffrent packaging and call the makers to see if they could give you info.
On many long journeys have I gone. And waited, too, for others to return from journeys of their own. Some return; some are broken; some come back so different only their names remain.