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Keel Damage in Laying Hens

It is widely recognised that today’s laying hen has poor skeletal health. Specifically, damage and fracture of the keel bone (the prominent ridge on the sternum of flighted birds to which the powerful wing muscles attach) is increasingly considered to be one of the most significant welfare problems within the egg industry.

Bone fractures are known to be painful in humans and there is evidence that fractures are also significantly painful in chickens (1). As well as being painful, keel bone fractures also interfere with bird behaviour (hens with broken keel bones take longer to walk from place to place, and take longer to both fly up onto, and down from, perches (2)), and affect egg production (decreased quality and quantity of eggs).

One study that investigated bone damage in laying hens in the United Kingdom (UK) (University of Bristol; Defra project AW0234 (3)) found that 36% of hens from furnished cages (cages that are larger than traditional 'battery' cages and have certain extra provisions, e.g. a nest box, to meet certain legislative criteria) had a keel bone fracture, and this figure was even higher in non-cage systems (classed as free-range, barn and organic), in which prevalence levels were between 45 and 86%. There are approximately 37 million birds in the UK flock; with 51% of egg production coming from birds kept in furnished cages and 44% from free-range (the remainder are kept in barn or organic systems) (4). Therefore, it is likely that around 6.7 million birds in enriched cages and between 8.3 and 15.9 million birds in non-cage systems are suffering from a broken keel bone. If one considers the numbers of laying hens on a global scale, then the suffering is even greater – egg production is big business, and in 2013, 7 billion laying hens produced 68.3 million tonnes of eggs throughout the world (5).

The modern laying hen is susceptible to bone fractures in part due to selective breeding for increased egg laying – both in number of eggs, and in length of laying cycle. A laying hen today is capable of producing around 300 eggs during a much extended laying cycle (usually lasting between 20 and 72 weeks of age) and this enormous and consistent production causes progressive bone loss from a bird’s skeleton as calcium is mobilised for egg shell formation. The Farm Animal Welfare Council (6) state that a laying hen’s need for calcium can exceed her body reserves by about 30 times.

Additionally, the environment that hens are kept in can contribute to fragile bones, such as when movement is limited in battery cages. Although the traditional ‘battery’ cage was banned in the EU in 2012 (Council Directive 1999/74/EC), the top three egg-producing countries (China, the United States of America, and India) still rely heavily (over 90%) on battery cages for egg production. Battery cages also contribute to poor hen welfare by preventing birds from satisfying a number of species-specific behaviours (such as nesting, scratching, and dust-bathing).

Overall, it is thought that the welfare of laying hens within the EU has been improved through implementing a ban on battery cages. Additionally EU legislation requires that all birds are allowed access to: a nest; perching space; litter (to allow pecking and scratching); and unrestricted access to a feed trough. These changes have allowed laying hens to have greater freedom of movement and to satisfy species-specific behavioural needs. However, the risk of keel bone damage is greater in furnished cages and alternative systems, when compared to battery cages, and complexity of the environment (e.g. type, number, and position of perches) is known to be a contributory factor to keel damage. Other factors that impact on keel damage include: nutrition (e.g. levels of dietary calcium and Omega-3 fatty acid); handling (e.g. during catching and removal from cages) and genetics.

There is still a great need for further research to both elucidate and disseminate other factors important in the causation and prevention of keel bone damage.

Examples of UFAW supported projects in this area: 

In 2014 UFAW supported an ‘International Workshop on Keel Bone Damage in the commercial laying hen’ in Switzerland. One output from the workshop was a guidance leaflet on ‘Perch Designs for Alternative Egg-Producing Systems’. This leaflet provides information on how to provide perches (which are a requirement for laying hens under EU legislation while addressing some of the housing issues that contribute to keel damage within these systems.

More recently UFAW made a research award to Ms Elena Armstrong at Newcastle University to develop a novel approach to “welfare markers” used to assess the wellbeing of food animals. This project will test whether changes in the birds’ brains reflect their levels of stress and whether the changes can be used as a measure of the  chickens’ lifetime welfare.

Selected paper on keel damage in laying hens published in the UFAW Journal, Animal Welfare:

Riber, AB and Hinrichsen, LK. Keel-bone damage and foot injuries in commercial laying hens in Denmark. 2016. Animal Welfare V25(2), pp 179-184. DOI: http://dx.doi.org/10.7120/09627286.25.2.179


  1. Nasr, M.A.F., Nicol, C.J., and Murrell, J.C. Do Laying Hens with Keel Bone Fractures Experience Pain? 2012. PlosOne: http://dx.doi.org/10.1371/journal.pone.0042420.
  2. Nasr, M.A.F., Murrell, J., Wilkins, L.J., and Nicol, C.J. The effect of keel fractures on egg-production parameters, mobility and behaviour in individual laying hens. Animal Welfare. 2012 (21): 127-135. ISSN: 0962-7286.
  3. Department for Environment Food and Rural Affairs (Defra). Detection, causation and potential alleviation of bone damage in laying hens housed in non-cage systems – Defra Science and Research Project AW0234. Research project final report available at: http://randd.defra.gov.uk/Default.aspx?Menu=Menu&Module=More&Location=None&Completed=2&ProjectID=12670.
  4. Department for Environment Food and Rural Affairs (Defra). National Statistics. United Kingdom Egg Statistics – Quarter 1, 2016. May 2016. Available at: https://www.gov.uk/government/statistics/egg-statistics.
  5. FAO (2016). FAOSTAT database collections. Food and Agriculture Organization of the United Nations. Rome. Accessed 30 June 2016. http://faostat3.fao.org/.
  6. Farm Animal Welfare Council. Opinion on Osteoporosis and Bone Fractures in Laying Hens. December 2010. FAWC. Available for download at: https://www.gov.uk/government/publications/fawc-opinion-on-osteoporosis-and-bone-fractures-in-laying-hens. or by contacting the FAWC at the following address: Area 5E, Nobel House, 17 Smith Square, London, SW1P 3JR.