Pull the salt blocks. They'll eat the mineral mix then.
Those red 'trace-mineral' salt blocks aren't really much of a mineral supplement - not much in the way of 'trace minerals' in there, and the cows can't lick enough off the blocks to get what they really need.
And, depending upon where you're located and what your soil/forage mineral content is, they can actually make copper deficiency issues worse.
They're 'red' because iron oxide is added as a filler/coloring agent; iron deficiency is not an issue in most parts of North America - and iron oxide is not a form that cattle can absorb or use - but it can block copper absorption sites in the intestine.
It's a big enough problem here that most folks would be better off with a plain old white salt block than a red one - but a good, balanced, loose mineral mix, formulated for need in your area is better.
Above all, you must remember that mineral supplementation needs are LOCAL. What is ideal for someone in, say, CO or MT, will not be the ideal formulation for producers in KY, TN, etc.
Most quality mineral mixes are formulated with a certain % salt to encourage consumption, but limit consumption so they don't 'overconsume' the mineral.
Usually no need for additional salt - though I do have to 'cut' mine with salt during winter - we limit feed hay/ddg, so the cows are standing around, bored, for 20 hours or so waiting for their next feeding, and will overconsume mineral (I can't afford THAT!), just because they've got nothing else to do/eat.
