I used to have links to more studies about feeding excess calcium to growing chicks. This is not the best one but it's the only link I have left. These places are constantly upgrading and improving their storage and online access so the links are often broken. I'm not going to spend the time searching for more studies.
http://en.engormix.com/MA-poultry-i.../avian-gout-causes-treatment-t1246/165-p0.htm
Anyway, there are studies out there that show excess calcium can sometimes injure growing chicks. I'm trying to be careful how I phrase that, there is enough panic o this subject already. These studies show that if growing chicks are fed feed with the amount of calcium in Layer feed chick mortality increases. This does not mean every chick dies. It means that they raise different groups of chicks as identical as they can with the only difference being that one group is fed nothing but feed equivalent to Layer and the other is fed an equivalent feed but with the calcium content closer to 1% as opposed to the approximately 4% calcium in Layer.
In the group with the 4% calcium the number of chicks that died was higher than the number of chicks that died when fed 1% calcium. They raised several batches like this. The results were consistent across the different batches. They also cut some chicks open at various ages to inspect internal organs. Again the results were consistent, more chicks in the 4% group had more kidney or liver damage than the chicks in the 1% group.
What can we learn from this? Not all the 4% chicks died. Not all the 4% chicks had internal damage. But enough did that it was clear that feeding them Layer can cause damage to growing chicks and should be avoided.
Another important thing is that one bite will not kill them. The damage is cumulative. The longer they are on that diet the worse it is. One study I saw did not start feeding them the excess calcium until the chicks were 5 weeks old. Other studies started at hatch. The numbers might have been different but the conclusion was the same. Feeding growing chicks that much calcium can harm a growing chick.
One important thing is that these chicks in the studies were fed nothing but the high calcium feed. It is not about how much calcium is in one bite, it's about how many total grams of calcium they eat all day, and even that is averaged out over several days. The more their diet consists of low calcium foods the less the total amount of calcium is so the smaller the chance of damage. If we are raising ours in brooders we are providing everything they eat so they may be getting a lot of calcium. But if they are being raised where they can forage for a lot of their feed the amount of high calcium feed they eat may not be very much. This is especially true with my chicks raised by my broodies. These chicks get some feed first thing in the morning and may get one more feeding later in the day but my broodies keep them out foraging the rest of the time.
I don't feed Layer at all. I feed Starter or Grower to everyone with oyster shell on the side for the ones that need it for egg shells. Even if I did feed Layer I don't think my broody-raised chicks would eat enough to harm themselves. My brooder-raised chicks would be different. But since I don't know I don't take a chance and avoid Layer.
@hellfire from your post I'm not convinced the difference in size is due to calcium. How did you feed yours, especially what protein levels and how much foraging did they do? My guess is that he fed them a pretty low protein diet with that corn and those greens. It's also possible since they were not heated after the first week that may have set them back some but I don't know what temperatures they went through. They were raised differently from yours, it's no surprise they are different.
How would I feed them from now on? On your regular diet. If any harm has been done it is already done. If it is malnutrition they may never get as big as they could have on a different diet but they should straighten out and thrive on your diet. I just don't see any other option.
