Keel bone damage and associated physiological parameters in traditional chicken breeds and hybrid layers

Introduction Keel bone damage is an important welfare issue in laying hens. Although some risk factors have been identified, the etiology is not fully clear. In previous studies, traditional breeds exhibited less keel bone fractures than hybrid layers. Aim Thus, this study aimed at finding out more about potential influencing factors by comparing two traditional breeds, Rhode Island Red (RHO) and American Leghorn (AL), and the two different hybrid layers Lohmann Brown Classic (LB) and Lohmann Sandy (LSA) in terms of keel bone damage and potentially related parameters. Methods The animals were kept in groups of 12 hens and one or two roosters, under natural daylight conditions, and with access to outdoor enclosures. Blood sampling was conducted at five and radiography at six time points between the 16 th and 72 nd week of age. The radiographs of the keel bones were evaluated for keel bone fractures, deviations, radiographic density, ossification, and length. Furthermore, the concentration of blood ionized calcium and plasma total calcium, phosphate, 17β-estradiol, and follicle-stimulating hormone (FSH) was measured. Results The overall prevalence of keel bone fractures was significantly higher in LB and LSA (90.1% and 87.5%, respectively) compared to RHO (0%) and AL (9.1%). RHO were larger and started laying distinctly later than the other genotypes. In addition, prolonged weight gain and less progressed keel bone ossification in the 24 th week of age compared to the other genotypes indicate slower physical development. The results on radiographic density, ossification, and age at first egg indicate that ossification and possibly mineralization were less progressed in the hybrid layers than in AL at onset of lay. Plasma 17β-estradiol increased around the onset of lay, but did not significantly differ between the genotypes during the laying period. Furthermore, between the 33 rd and 52 nd week of age, there was a significant increase in plasma FSH in all genotypes, which may be attributable to seasonal changes in the length of daylight. Discussion/Conclusion In summary, this study offers insights into keel bone health, bone traits, and reproductive parameters in different chicken genotypes, which may improve understanding and contribute to future strategies to reduce keel bone damage.