Histomorphological characteristics of keel bone maturation and keel bone fractures in laying hens

The keel bone in laying hens is prone to fractures, especially on the caudal third of the keel, which is also the last part to ossify. Keel bone fractures (KBF) typically occur between 25 and 50 weeks of age (WOA). However, the keel is fully ossified at around 40 WOA, suggesting fractures can occur before ossification is complete. To better understand the relationship between KBF and ossification, this descriptive study examined keel bone morphology during maturation. Keel bones from 50 commercial aviary housed Dekalb White laying hens were collected at 10 timepoints from 17-53 WOA and prepared for histological analysis. The samples were stained with haematoxylin and eosin and Safranin O to show cartilage, ossification, bone tissue, and KBF. The results indicated an ossification process similar to endochondral ossification. The degree of ossification varied between individuals of the same age. The age at complete ossification varied from 28-49 WOA. None of the keels from hens aged 53 WOA were fully ossified. Cartilage canals were present in the keel cartilage. Medullary bone was observed in all age groups. Most fractures lacked tissue morphologies typical of high-impact collisions, suggesting the need for further research into the underlying causes. This is the first study to detail keel bone histomorphology in commercial laying hens, providing baseline data for future research.