Should you give grass fed cows mineral blocks and salt licks all year long?

This is a very important thing to do, yes, because the grass they eat doesn't have all the necessary minerals they need: they need to get it in either loose or block form. Ideally, summer time is best for blocks, and winter for loose, but you can feed loose and/or block all year round, your choice. Just note that mineral blocks have 95% salt in them, not nearly as much mineral as the loose form would have.