I have been creep feeding for years. The benefits are there. Documented data, creep fed calves will finish with a higher marbling score, once a fat cell is created it stays, only changes in size. Yes you can have heifers deposit fat in their mammaries which can influence milk production later in life, if they are that fat they sure do not need to have creep feed in front of them. FH, I have a different view, I think of the cow as the calf factory, the calf is way more efficient converting feed to meat than the cow, I choose to feed the calf, the cow is more of a companion after a couple of months, in my feeding trials at MSU, the correlation of milk production to weaning weight is very weak, the calves eat more than people believe and rumen cannulated calves proved this. Weaning weight was more correlated to sires and the amount of forage consumed by the calf than milk production of the dam. The calves that learned to eat forage and therefore ate forage earlier were the heaviest at weaning.These calves tended to come from cows who did not milk that well.
Since we fall calve, the creep feeders are filled at about 2 months of age, the calves are eating right away. They learn how to eat and what to eat, then the cows can get by on less feed and not lose condition. We wean early, average age 170 days, the calves know how to eat, therefore wean easy, the cows don't. To get past the bloat problems with creep feeding, we add Poloxalene to the feed at the feed mill, for a cost of about $10 per ton. We do not use rumensin in the creep feed because it is bitter and tends to keep the calves from eating. If they are eating too much of the creep feed, shut the gates on the creep feeder down so it is harder to get the pellets out into the tray. I would never creep feed whole grains, there is an effect where grains decrease the breakdown of fiber in the forage which in effect gives you a substitution, not a supplementation. Wheat mids make a good ingredient in creep feeds as they are a highly digestible fiber, not a starch.
We also give Alpha 7 at birth, have not had a case of overeating for about 10 years doing this. Our calves get another at weaning, and one when they get to the feedlot, one half way through and that is it. Our calves come off the truck at the feedlot looking for the feed bunk and our death loss is usually 0.