They won't put on weight as quickly with more grass hay (alfalfa/clover is another story) because they aren't being pushed by extra protein and nutrients so for showing purposes they may not make senior weight when you want them to. This does not mean there is a health issue. In fact they may be healthier growing slower and reaching a slightly smaller size but it doesn't serve human purposes for them because we want them big. Feeding alfalfa/clover can put on weight and increase growth speeds so not all hay will make a skinny rabbit. Some hay will make a fat rabbit. The people raising full size commercial types are often against feeding hay because all they can get is grass hay which doesn't grow them out fast enough and the people with dwarf or mini breeds are often against hay because all they can get is legume hay which makes them fat.
We feed them as individuals and I'm quite happy with the results we've gotten. We hand pick bales with varying amounts of clover, alfalfa, or grass. Clover can go as high as 30% protein. We feed the mini rex bucks the nearly all grass hay and the growing meat rabbits nearly all clover hay with everyone else somewhere in between. Aside from differences in hay a fatter rabbit will have their concentrates cut and no high fat items added and a skinnier rabbit will get unlimited concentrates with possibly some black oil sunflower seeds. We don't feed x cups for this breed of rabbit. I feed the rabbits like I do my horses by evaluating body condition and how much of each feed was eaten and adjusting for that individual on a daily basis. When you butcher a rabbit you see things that are not apparent in the live rabbits. You can see low levels of cocci, parasites, or damage to the liver and lungs by ammonia buildup under cages. Muscle tone, fat percentage... I was happy with all of it on the ones I butchered a few days ago. Both the colony and cage raised rabbits had dark red livers, evenly tinted lungs, good muscle tone, and just enough fat for the time of year. I have some beautiful argente and mini rex pelts in my freezer now too. It might not be as simplistic as dump x cups of pellets in each feeder every day but you can't argue the results and it's a whole heck of a lot cheaper to feed them on organic clover hay with bulk purchased grains than 18% rabbit pellets.
