Travlr, we thought as you did at one time.
We OURSELVES experienced what happens without a quality mineral program.
If you don't feed loose mineral, you are walking a tightrope. Something could change to cause a fall. It happened to us in 1988 and went on for 6 years. It took a mineral program to save our cowherd and our sanity. We even moved across the state and we had the same problems with our calves getting sick. It's a long story and I won't go into it here.
The University of Montana did extensive studies in MT and found the soil is lacking in copper and zinc. They are non-biased. They printed papers, did on-site visits, pulled blood, and their recommendation was to feed a year-round (loose)mineral program. They found sulfates in the water which ties up copper and zinc and compromises the immune system. The sulfates in the water was picking those guys pockets. They were leaving money on the table when considering death loss, breeding back, losing longevity in their cows, herd health (hoof rot, overeating, scours, etc was helped/eliminated by merely feeding a quality loose mineral). They picked that money back up by feeding mineral. I had a customer tell me when he was working on taxes, "my mineral column cost has gone up but my veterinary column has gone way down. My life is better because I'm no longer doctoring sick cattle". There are many benefits that make it feasible to feed loose mineral.
We can prove that a year-round mineral program adds weaning weight to the calves, and even more so when something is used to control flies. This isn't just ME saying this, this is feedback from ranch customers. They do what pays, they don't buy mineral because they like me. They buy it because it works. We have done ranch trials, not laboratory trials to document the difference between ranchers not feeding mineral and feeding loose mineral. Feeding loose mineral won out every time.
As for blocks...studies have been done that show that cattle, horses, etc cannot lick enough in a day to get their salt requirement. A kid at UW got a grant to count how many licks a cow will do before they get tired and walk away. It was like 2000 licks to get an ounce of salt, don't quote me on that because that was a long time ago. He sat in a corral with the only source of water. By that water was the salt blocks. He had a clicker and he clicked it every time a cow licked on the salt. Some places cattle will eat more salt, some places less due to the salt in the soil.
We have taken loads of soil samples over the years. Only on one ranch did we find the need for a custom mix mineral. All the other places a standard mineral worked fine. There are exceptions to everything.
When the grass dries up in late summer, the nutrients have gone out of the forage. A different formula needs to be used then. So basically 2 different levels of phos--4% phos can be used in spring, but later in the summer they overeat the 4% so our customers go to a 6% mineral. Phos is a limiter so 2% more phos will help with over consumption. Therefore, it's not complicated. Producers can add whatever they want to the basic formulas. For example, IGR, CTC, BioMoss, Magnesium...
We used our mineral consumption as a management tool. When the cattle started over consuming in a pasture, they were showing us the goodies were gone and we moved them to a fresh pasture they backed off the mineral.
In most cases, a good vitamin pack is included in mineral. Vit A, D3 and Vit E all contribute to a healthly herd.
Trvlr, you go ahead and do what you are doing. I can tell your mind is made up. I'm replying mostly to counteract some misconceptions in your posts.
Can cattle survive without adding loose mineral. Sure they can. They have. That's when fall calves weighed 300# and it didn't matter if several cows ended up open or died. Ranchers ran their yearlings til they were 2 years old back then. Today none of that it economically feasible.
We, along with many others, have seen and experienced first-hand the value of a quality year-round mineral program.
Edited to add: Western SD is high in selenium so mineral sold there is w/o selenium. Travlr, I thought you might know that since you lived near there.