Deere is correct - we're doing it at places where they feed a TMR year round.  They are not necessarily in dry lots year round, because of pasture costs many will double stock their pastures and supplement it with a TMR.  Best of both worlds, clean grass for the cows and calves plus you can control the nutrition better.
There are some free choice minerals with Rumensin (all are exactly the same, following an FDA formula) but my experience is they don't eat it very well.