The Influence of Keel Bone Damage on Welfare of Laying Hens

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.

Keel bone fractures induce a depressive-like state in laying hens

“…The alternative interpretation is based on the assumption that healed breaks remain somewhat painful, and therefore stressful, over a hen's lifetime. Indeed, existing KBFs may often be repeatedly aggravated during normal hen behaviour, such as movement to food or water, flight and perching 15 . If this is the case, through integrating older and newer fractures, severity score at the final time point in itself reflects the cumulative pain or discomfort experienced.…”

A Reliable Method to Assess Keel Bone Fractures in Laying Hens From Radiographs Using a Tagged Visual Analogue Scale

“…Our scaling tool does not include specific fracture characteristics relevant for clinical examinations (e.g., fracture location), but provides a simplified measure of cumulative damage and therefore aggregate severity of individual hens. While there is evidence that the presence of keel bone fractures has a negative effect on multiple aspects of laying hen welfare [reviewed by Riber et al ( 3 )], it remains unclear how the severity of fractures affects an individual hen. Thus, as suggested by Harlander-Matauschek et al ( 48 ), our scaling tool must be validated regarding the effect of fracture severity on various animal welfare related indicators (e.g., pain, affective states) as well as other responses of interest (e.g., productivity).…”

“…Keel bone fractures in laying hens are an important welfare issue because of their likely association with pain and suffering ( 1 – 3 ). Due to the scope of the problem with reports of 97% of laying hens within a flock manifesting fractures ( 4 ), multiple research studies investigating prevalence, causes, risk factors, and consequences of keel bone fractures have been conducted in recent years.…”

Keel fracture changed the behavior and reduced the welfare, production performance, and egg quality in laying hens housed individually in furnished cages

“…However, their usage can lead to some welfare and health problems such as keel damage (including keel fracture and deviation) ( Rørvang et al., 2019 ). Some studies have shown that keel fractures cause pain and stress response ( Riber et al., 2018 , Wei et al., 2019 ). The incidences of keel fractures increase with the hen's age, with a peak record during laying period, which gradually decrease after 42 wk of age ( WOA ) ( Gebhardt-Henrich and Fröhlich, 2015 , Stratmann et al., 2015 ).…”