It does matter what the cattle are fed.
Generally speaking....I find there to be a big difference between the fat on a grass fat and grain fat beef.
The grass fat animal normally has a stronger flavor....some people describe it as gamey. I personally can find not a single thing wrong with some of the grass fat animals that I have raised. I like the strong beef flavor.
There is grass fat and then there is grass FAT! The quality, and quantity of the grass makes a huge difference.
The beef you eat in Montana is probably grain fat unless otherwise specified. A great deal of that beef is barley finished.
The fat of these animals all tastes different.
Also, generally speaking....the least amount of time an animal will hang after killing is a week to ten days.
Two weeks is average at a locker plant. Three weeks is better yet.
Very little beef is consumed truly "fresh".
My guess would be that you are eating animals that have been fed/grazed vastly different finishing rations. The freshness of both animals was probably pretty similar.
