Calcium on its own is not enough, for conversion into bone, it also requires Magnesium and vitamin D. but the amounts are finely balanced. Silicon is also required to produce the synthesis of these into the metabolism plus Selenium to stimulate brain and Pituitary function for ongoing bone production. The cure isn't that complex, once you understand how it all works, the answer most likely lay in the pre-breeding season diet. Today it is fashionable to winter feed upon an impoverished calcium, magnesium, Vit. D. and silicon deficient diet.
Bone is produced continually, throughout life, with a gradual decrease in later years.
I myself am becoming the 'incredible shrinking man' having lost three inches from my height since my teens, partly to do with gravity and closing gaps between joints, but mainly because of decreasing bone replenishment. This is why sons are almost always two inches taller than their fathers who were once giants of men in their eyes. However I digress. The correct diet allows a body during its early years of life to maximise bone production for the time when tissue loss occurs. In humans this happens in mid life, producing a decrease in height or distortion of frame, with pigeons much sooner, so diet plays an important role at all times, not just the breeding or racing season.