Comparison of Keel Bone Traits, Eggshell Production, and Physiological Parameters between a Hybrid Layer and Two Low-Performing Chicken Genotypes

Lisa Hildebrand^1*Saskia Neukirchen²Mareike Fellmin³Julia Mehlhorn⁴Stefanie Petow⁵Lars Schrader¹Steffen Weigend^6,7Beryl Eusemann-Keller⁸

• ¹Institute for Animal Welfare and Husbandry, Friedrich-Loeffler-Institut, 29223 Celle, Germany
• ²Institute for Animal Science – Farm Animal Ethology, University of Bonn, 53115 Bonn, Germany
• ³Poultry Research Center, Bruno-Dürigen Institute, 41569 Rommerskirchen, Germany
• ⁴Institute for Anatomy I, Medical Faculty and University Hospital Düsseldorf, Heinrich Heine Univeristy Düsseldorf, 40225 Düsseldorf, Germany
• ⁵Chair of Animal Welfare, Ethology, Animal Hygiene and Animal Husbandry, Department of Veterinary Sciences, Faculty of Veterinary Medicine, Ludwig-Maximilian-Universität, 80539 Munich, Germany
• ⁶Institute of Farm Animal Genetics, Friedrich-Loeffler-Institut, 31535 Neustadt-Mariensee, Germany
• ⁷Center for Integrated Breeding Research, University of Goettingen, 37075 Göttingen, Germany
• ⁸Faculty of Veterinary Medicine, Institute of Animal Hygiene and Veterinary Public Health, Universitat Leipzig, Leipzig, Germany

Keel bone damage is a severe animal welfare problem in laying hens. Although it is influenced by husbandry and diet, the selection for laying performance seems to play a key role. In order to learn more about the pathogenesis of keel bone damage, this study aims to characterize and compare keel bone health and potentially related traits in Lohmann Selected Leghorn (LSL, n = 12) and two low-performing genotypes that have not intensively been selected for laying performance: Junglefowl phenotype (JF, n = 14) and Sumatra (Su, n = 12). X-ray imaging, blood sampling, and ultrasonography were conducted at five different time points between the 16th and 72nd week of age. The X-ray images were evaluated for fractures, deviated keel bone area, radiographic density, length, and ossification of the keel bone. Blood samples were used to determine blood ionized calcium, as well as plasma total calcium, phosphate, and 17-β-estradiol. Laying activity and eggshell quality were assessed at group level. Ultrasonography was used to detect visible follicles and assess pectoral muscle thickness. Keel bone fractures were detected in five out of twelve LSL hens, but in none of the two low-performing genotypes. The first egg was laid distinctly earlier in LSL than in JF and Su (18th vs. 24th and 31st week of age, respectively). Keel bone ossification was completed significantly later in Su than in LSL and JF, but there was no significant difference between the latter two. Visible follicles at the ovary were associated with significantly higher plasma calcium and 17-β-estradiol levels. This study provides a deeper insight into keel bone health and related traits in LSL and low-performing chicken genotypes. Our findings indicate that the earlier onset of lay in LSL does not correspond with earlier keel bone maturation, which could increase later susceptibility for keel bone fractures.