most of the old timers around here don't feed mineral, and some have really nice herds of commercial cows. They have culled cattle for years that didn't work, instead of propping them up with feed and minerals. I'm not saying that's the way to manage your herd, but I know it works. When did supplementing cattle with minerals become a management tool?
Grazing KY 31 fescue? Endophyte infected KY31 is a whole different animal than other grasses.
The mineral needs are largely based on the soils and the forages where you are or should be. Once you know or can tell by observations you know that they deliver the needed supplements to the cows. In KY 31 with endophyte, the endophyte apparently masks or can interfere with copper absorption. And I think it is copper that needs zinc in combo and in quantity to be utilized. Find a chart of the US that shows selenium status of the soils. That will also help you decide if you need maximum selenium as allowed by law. So it is not all easy science.
There are plenty of good minerals around but you need to learn to read tags and get what you want. We have a group that bulk orders from a regional manufacturer and get a high grade mineral for lot less than discussed here but it is not the cheapest either. You get what you pay for if you shop around and do not get hung up on a brand name. And a lot of the elements and such are based on China prices and sources in some cases.
The easiest way to know if your cattle need minerals are observations. Do 90% (or your threshold) of them breed back on time. Are black calves born with red hair coats? Do cows and calves shed later than you want? Do your cows live in the pond in the summer or only graze in the evening and at night? Do your cows lose hooves, tail switches, walk on tip toes, pant and struggle in the summer?
Opinions: I will not do injections on minerals. A waste of my time if all of my goals are met via loose minerals. This is an opinion also: some of the higher performance type cattle probably need more mineral inputs and higher quality to retain their honor. We see that in the dairy industry where minerals of the chelate form are widely toted along with the yeast source of selenium.
As some have said, find the cows that work for what you are willing to spend and either make money or have bragging rights. But we could not run cattle as economically here if we did not use decent minerals. As an old co-worker used to say, " Been there, done that".