I've been away for a few days. Let me clarify my post. My point wasn't so much against feeding grain, as it was giving some perspective to those who accuse you of mistreating your calf.
Some general comments, some already covered by others:
Too much hay does not cause disease. But in a young calf, they cannot eat enough to extract the necessary energy and protein they need for growth. That's why they normally continue nursing until they get a bigger rumen – relying on their mom's big rumen to extract nutrients that go into milk.
The lower the quality of hay, the more is needed. Give calves all the hay they can eat, so they can extract as much as possible – but they'll still need more nutrients through grain.
I bought a lowline/Jersey 6-month old heifer. The guy was promoting the lowlines as only needing grass. Well, he had weaned the heifer at 3 months and thereafter was only giving her grass hay, and she looked pretty poor – pot-bellied and lacking muscle. I got her home and started alfalfa hay and some fortified grain ration and she perked right up. Adults with big rumens can live on just grass, but not calves.
Too much grain can be a problem. It is more of a problem at a later age when the rumen is more developed and contains more microbes. The microbes convert the starch in grain to acid which can cause problems. Always want to introduce grain slowly so microbes can adjust, and better if divided into multiple feedings. Feedlot/dairy rations are mostly grain, so the amounts you're feeding are fine.
Here's some readable info on rumen development and function:
http://www.cattletoday.com/archive/2000 ... ay85.shtml
http://www.cattletoday.com/archive/2000 ... ay88.shtml