Department of Veterinary & Animal Sciences, University of Copenhagen, Copenhagen, Denmark.
Danish Agriculture & Food Council, Copenhagen, Denmark.
PLoS One. 2021 Aug 13;16(8):e0256105. doi: 10.1371/journal.pone.0256105. eCollection 2021.
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.
商业家禽生产系统中的龙骨骨折（KBF）是一个主要的福利问题，可能对家禽业造成经济后果。最近的调查表明，这种情况可能正在恶化。根据饲养系统的不同，来自不同国家的报告骨折发生率超过 80%。由于尚未确定具体原因，因此这阻碍了风险因素的识别。本研究的目的是调查丹麦蛋鸡中 KBF 的流行情况，并确定所有主要生产系统（包括种鸡生产）中与 KBF 相关的风险因素。为了进行风险因素识别，使用了纳入鸡群的生产数据。总共在产蛋期末对 40 个鸡群中的 4794 只鸡进行了调查。所有鸡只在农场进行安乐死，并进行检查和触诊，然后进行剖检。所有观察结果均记录下来，并随后使用 SAS 统计软件包进行分析。在非笼养系统的鸡群中，观察到骨折发生率在 53%-100%之间，而在丰容笼养系统的鸡群中，骨折发生率在 50-98%之间。此外，根据鸡群的不同，经常在个别鸡只中观察到多个骨折（≥4 个）（有骨折的鸡只中 5-81%）。在所有鸡群中，骨折均位于龙骨远端（>96%），位置高度一致。宏观上，骨折的形态从无骨痂形成的外观（最常发生在笼养鸡中）到骨折线周围和内部的大骨痂形成，这是无笼养鸡的典型表现。尽管处于无笼饲养条件下，种鸡的每只鸡骨折数（所有鸡群均为 60 周龄）明显少于无笼饲养系统中的其他鸡只。产蛋期末的体重对发生骨折的风险有影响，体重较重的母鸡产蛋期末的骨折数明显减少。母鸡开产时的年龄越大，产蛋期末的鸡群发病率越低。此外，开产时的日产蛋重对发生骨折的风险也很重要，最初产较大的蛋会导致淘汰时的骨折发生率更高。体重（增加 100 克）的优势比为 0.97，开产时的年龄（增加 1 周）为 0.87，开产时的日产蛋重（增加 1 克）为 1.03。总之，本研究表明，所有生产系统中的母鸡都存在很高的 KBF 发生率，并确定了母鸡体型、开产时的年龄和开产时的日产蛋重是现代蛋鸡发生 KBF 的主要风险因素。需要进一步研究这一点，以增强蛋鸡的寿命并提高其福利。
