well , if this is true, grass finished but grain fed is far far better than just grain fed. After 3 months I believe with what I've read that it's almost as good as pure grass fed. People seem surprised here but it DOES make some sense. A grass fed cow will take about 2 years or thereabouts to mature to slaughter weight whereas a grain fed cow takes about half that long. Maybe this is some attempt to speed the process but retain the better fat profile? theoretically if this is true speaking.
One test should be if the cows ever receive antibiotics. If the cows don't ever need antibiotics, then they aren't eating enough grain to mess up system. My preference is to go with 100% grass fed beef. But grass finished may be good enough depending on the situation.
So the animals are pastured but the farmer supplements with grain? Did they say why they have to supplement when they're already on pasture? Normally they would just supplement with hay (dried grass) not grain if they're already on pasture. Especially since they can get a higher price for 100% grass-fed beef.
Our locally owned health food store with butcher inside has this same type of beef (grain fed, grass finished), and I've never understood why farmers would do it this way. I ended up buying 100% grass fed from a local farmer instead. The taste is much better, as well as nutrient profile.
Usually it is the other way around....a grassfed animal is raised on grass til about 500-600 pounds and then is sold off and shipped off to a feedlot to be grain finished. That process takes about a year to a slaughtered animal...whereas a totally grass fed animal takes about 18 months for it to get to slaughter weight of plus or minus 1200 pounds...thus the higher cost for grassfed.
Being grain fed first and then grassfed to finish...I can't imagine farmer doing it this way.