If your dog eats good brand commercial dog food , it is not necessary to give additional calcium or phosphate. Too much these two elements will induce some developing bony diseases in young growing dogs.
For CHD dog, if there is active damage of bone which additional calcium will increase the formation of osteophytes(new bone ) and make the 2nd degenerative joint disease getting worse.
Sometimes we will ask CHD dog has more calcium to help to buid up stronger bony condition for Total hip replacement but only if there is no active inflammation and bony damage existing.
Dr. Lee from Elwood animal medical group U.S.A.