Abstract
This article reviews current knowledge about welfare implications of keel bone damage in laying hens. As an initial part, we shortly describe the different conditions and present major risk factors as well as findings on the prevalence of the conditions. Keel bone damage is found in all types of commercial production, however with varying prevalence across systems, countries, and age of the hens. In general, the understanding of animal welfare is influenced by value-based ideas about what is important or desirable for animals to have a good life. This review covers different types of welfare indicators, including measures of affective states, basic health, and functioning as well as natural living of the birds, thereby including the typical public welfare concerns. Laying hens with keel bone fractures show marked behavioral differences in highly motivated behavior, such as perching, nest use, and locomotion, indicating reduced mobility and potentially negative affective states. It remains unclear whether keel bone fractures affect hen mortality, but there seem to be relations between the fractures and other clinical indicators of reduced welfare. Evidence of several types showing pain involvement in fractured keel bones has been published, strongly suggesting that fractures are a source of pain, at least for weeks after the occurrence. In addition, negative effects of fractures have been found in egg production. Irrespective of the underlying welfare concern, available scientific evidence showed that keel bone fractures reduce the welfare of layers in modern production systems. Due to the limited research into the welfare implications of keel bone deviation, evidence of the consequences of this condition is not as comprehensive and clear. However, indications have been found that keel bone deviations have a negative impact on the welfare of laying hens. In order to reduce the occurrence of the conditions as well as to examine how the affected birds should be treated, more research into the welfare implications of keel bone damage is needed. Research should focus on effects of genetic lines, genetic selection, housing, and nutrition for the development, prevalence, and severity of these conditions, preferably conducted as longitudinal and/or transnational studies.
Highlights
In modern egg production, laying hens (Gallus gallus domesticus) face a number of clinically evident welfare problems, of which keel bone damage is among the most prevalent
We aim to review the current knowledge about welfare implications of keel bone fractures and keel bone deviations, respectively, in laying hens in modern egg production
We focus on animal-based measures, covering the following categories of welfare indicators: hen behavior, physiology, clinical signs, production parameters as well as indicators of the affective states of the birds
Summary
In modern egg production, laying hens (Gallus gallus domesticus) face a number of clinically evident welfare problems, of which keel bone damage is among the most prevalent. As discussed by Sandilands et al [1], selection for early sexual maturity and a continuous high egg production in commercial layer lines have led to increased bone fragility and susceptibility to fractures due Welfare Implications of Keel Damage to the high calcium requirement for formation of eggshells. The ossification process of the keel bone continues until approximately 40 weeks of age [5]. At 16 weeks of age as the hen begins producing eggs, several centimeters of the caudal tip of the keel remain entirely cartilaginous [6]. As large amounts of calcium are required for eggshell production, starting at the onset of lay, it is possible that—for high-producing layers—the cartilaginous keel bone receives less than adequate calcium for proper ossification during the early laying period. At present, data are not available to support this suggestion
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