good read Growth Disorders in Young German Shepherds | German Shepherd Dog Club of Victoria
"Osteochondrosis and joint dysplasias have been studied in many species, in particular in pigs. Where the animals were selected for increasingly heavy end weight and rapidity of weight gain, the higher the incidence of symmetrical lesions in certain sites in joints and many growth plates. Experimentally in pigs, the incidence and severity of OCD was directly related to rapid growth ie. rate of weight gain.
When the diet was restricted and grown at a low growth rate, the incidence of OCD was dramatically reduced (almost to zero).
All dog studies in this area have shown to support the concept that the high caloric intake rather than the specific intake of protein, minerals or vitamins influences the frequency and severity of osteochondrosis and HD. The causes of ED while not as thoroughly studied, show similarities and probably similar outcomes.
The common conclusion from studies in dog is that excessive calcium, phosphorus and vitamin D along with a high energy diet and rapid weight gain causing rapid growth, are almost an ideal recipe for pushing the parameters for normal structural growth and joint soundness well beyond their normal limits, resulting in joint disorders. The higher incidence of osteochondrosis in males versus females is probably a direct reflection of this as males are often ¼ heavier than females at any one time, despite being born at a comparative weight.
Equally, this is not to say that genetics does not pay an important part in the body’s structural soundness, however excessive rates of weight gain and thus rapid growth result in pushing the body’s parameters beyond which they can cope, particularly if they were not the most structurally stable to start with. That is, excessive rate of growth and weight will not create severe HD or ED in itself; however, it can make an existing problem considerably worse."