7-16. 較老的雞隻可能會有胸骨軟化的問題，胸骨也會因為鈣、磷或維生素D3不足而呈多孔樣構造。在這種情況下，坐在棲架上會導致胸骨變形。 Older chickens can suffer from a softening of the breast-bone. The breastbone also becomes porous as a result of calcium, phosphorus or vitamin D3 deficiency. Under these circumstances sitting on a perch can cause the breastbone to become deformed.