Keel bone fractures in Danish laying hens: Prevalence and risk factors

Abstract

Keel bone fractures (KBF) in commercial poultry production systems are a major welfare problem with possible economic consequences for the poultry industry. Recent investigations suggest that the overall situation may be worsening. Depending on the housing system, fracture prevalences exceeding 80% have been reported from different countries. No specific causes have yet been identified and this has consequently hampered risk factor identification. The objective of the current study was to investigate the prevalence of KBF in Danish layer hens and to identify risk factors in relation to KBF in all major productions systems, including parent stock production. For risk factor identification, production data from the included flocks was used. In total, 4794 birds from 40 flocks were investigated at end-of-lay. All birds were euthanized on farm and underwent inspection and palpation followed by necropsy. All observations were recorded and subsequently analysed using the SAS statistical software package. In flocks from non-caged systems, fracture prevalence in the range 53%-100%, was observed whereas the prevalence in flocks from enriched cages ranged between 50–98%. Furthermore, often multiple fractures (≥4) were observed in individual birds (range 5–81% of the birds with fractures) depending on the flock. The localization of the fractures at the distal end of the keel bone is highly consistent in all flocks (>96%). Macroscopically the fractures varied morphologically from an appearance with an almost total absence of callus, most frequently observed in caged birds, to large callus formations in and around the fracture lines, which was a typical finding in non-caged birds. Despite being housed under cage-free conditions, parent birds had significantly fewer fractures (all flocks were 60 weeks old) per bird, than other birds from cage-free systems. The body weight at end-of-lay had an effect on the risk of having fractures, heavy hens have significantly fewer fractures at end-of-lay. The older the hens were at onset of lay, the lower was the flock prevalence at end-of-lay. Additionally, the daily egg size at onset of lay was of importance for the risk of developing fractures, the production of heavier eggs initially, resulted in higher fracture prevalence at depopulation. The odds ratio of body weight, (+100 g) was 0.97, age at onset of lay (+1 week) was 0.87 and daily egg weight at onset (+1 gram) was 1.03. In conclusion, the study demonstrated a very high prevalence of KBF in hens from all production systems and identified hen size, age at onset of lay and daily egg weight at onset of lay to be major risk factors for development of KBF in the modern laying hen. Further research regarding this is warranted to strengthen the longevity and enhance the welfare of laying hens.

Abnormal Bone Metabolism May Be a Primary Causative Factor of Keel Bone Fractures in Laying Hens

“…This finding indicates that the occurrence of KBFs may be associated with the changes in the body weight of laying hens. Moreover, previous studies found that the bodyweight of laying hens affected the keel bone quality and vice versa [ 25 , 26 ], and the laying hens with fractured keel bone generally had a lighter bodyweight than those with a normal keel bone [ 6 , 18 ]. This finding was similar to our observation that the bodyweight of FK laying hens was lower than NK hens and reflects that the bodyweight is related to KBFs in laying hens.…”

“…Additionally, although the current study suggested that keel bone damage could be associated with abnormal bone metabolism reflected by changed serum markers in relation to bone turnover in laying hens, this study had limitations, such as the younger hens, a shorter experimental period, a smaller sample size, and the lack of the analysis of bone mineralization markers and serum RANKL level, as well as the age at onset of lay and the egg production of laying hens in each group. Previous studies reported that these factors could affect the development of KBFs in laying hens [ 26 , 45 ]. Besides, one of the most important limitations is the young age of the laying hens.…”

Commercial layer hybrids kept under organic conditions: a comparison of range use, welfare, and egg production in two layer strains

“…The most recent studies on keel bone fractures suggest that especially the fractures located at the caudal tip occur as a result of internal forces ( Thøfner et al, 2020 ). Hens with smaller bodies, an earlier onset of lay, larger egg size at onset of lay are thought to be at an increased risk of developing fractures in the caudal tip of the keel bone ( Thøfner et al, 2021 ). In our study, DW hens had an earlier onset of lay and smaller body size and experienced a greater number of fractures of the cranial section of the keel bone over the course of the study.…”

Productive performance, perching behavior, keel bone and other health aspects in dual-purpose compared to conventional laying hens

“… Gebhardt-Henrich and Fröhlich (2015) found that the younger hens were when laying their first egg, the higher was the probability of having a keel bone fracture at depopulation. A possible explanation for this finding is the late ossification of the keel bone at about 35 wk of age ( Buckner et al, 1949 ; Thøfner et al, 2021 ). At this age, hens have already been laying eggs for several weeks.…”

“…Keel bone damages, that is, fractures and deviations, can be found in all housing systems for laying hens. The overall prevalence in cage systems, single and multi-tier systems, and systems with access to free-range ranged between 3% and 100% of hens within one flock ( Donaldson et al, 2012 ; Petrik et al, 2015 ; Hardin et al, 2019 ; Jung et al, 2019 ; Thøfner et al, 2021 ). The presence of keel bone damage, especially fractures, can cause pain in laying hens ( Nasr et al, 2012 ), which can negatively affect hens’ mobility ( Rentsch et al, 2019 ) and welfare ( Dawkins, 2004 ; Riber et al, 2018 ).…”