No matter what is fed to cattle, as a producer you need to be able to "body condition score" your cattle. Cattle are scored from a 1-9. One being "dead thin" and 9 obese. Heifers due to calve should be about a 6.5-7 condition score so that they have enough reserve to come into milk & breed back after calving. Cows should be about a 6 score. When people say you shouldn't feed grain to close calvers, they are worried that the calf will get too big and cause dystocia. Research shows that cattle underfed were more likely to have difficulty calving & the calves are more likely to die, than cattle that were overfed. BUT, there is a happy medium. Too fat, too much protein & the calf gets bigger which leads to dystocia. It's one of those things that you need "just right". Look at your cattle, do they have large fat pockets on each side of their tailhead? Do they have round filled out briskets? Can you see ribs? or are they buried in an inch of fat? I have Simmental, and when my cows are in good condition they will "just" show a few ribs, spine nicely covered with meat & fat.
If you're cows are fat, I would cut down the amount I'm feeding if you need to get them to come up to a feeder each night to see them. If they're "just right" keep up what you are doing. I personnally couldn't affort to feed my cows ANY grain. They get good hay all winter & grass in the summer. Replacement heifers get grain until they are safe in calf in the spring.