It is a shame that this discussion continues to arise.
People here usually give advice based on experience and anecdotal evidence. That's fine - to a point.
Layers are females actively building egg shells. Those are the only birds that should be eating a feed high in calcium content. Namely, LAYER FEED. It is formulated for flocks where all birds are actively laying eggs.
The doubters can deny it all they want.
It is true that some lines of some breeds can handle excessive calcium better than others but - the fact remains that calcium content in a diet in excess of 2.5% calcium will cause kidney damage in non laying birds. That would be roosters, molting hens or any birds taking a long break from laying eggs. Layer feeds are normally between 3.5 and 4.5% calcium.
It is also a scientific fact that kidney damage can't be reversed.
The kidneys "recycle" calcium and serve to maintain an appropriate calcium/phosphorus blood balance.
IMHO, the reason many don't believe it, is that birds affected by urolithiasis exhibit no symptoms. A chicken has 2 kidneys with 3 segments each. As long as there are still two functioning segments, hens will continue to lay and any affected birds show no ill effects until one of the last two segments fails and they will die within 24 hours.
It is also a fact that most people don't have a necropsy done when a bird dies of unknown causes.
If the OP's friend had a necropsy done on her rooster that showed calcium damage, I would believe the avian pathologist over someone that feeds layer feed to roosters yet says it has no effect.
Purina poultry nutritionist,
Mikelle Roeder, Ph.D. says one shouldn't feed layer feed to roosters, molting hens or young birds and to switch to flock raiser if roosters are present.
https://www.purinamills.com/chicken...djust-nutrients-in-chicken-feed-as-birds-grow
When my last computer fried, I lost my more pertinent links showing the kidney damage from excess calcium intake in roosters and pullets/hens not actively laying but here are some others.
https://www.hyline.com/aspx/redbook/redbook.aspx?s=5&p=36
http://www.thepoultrysite.com/articles/2337/urolithiasis-in-male-broiler-breeders/
https://www.ncbi.nlm.nih.gov/pubmed/3585534
http://www.livestocklibrary.com.au/handle/1234/19522
https://www.tandfonline.com/doi/pdf/10.1080/03079458008418381