Review links keel bone damage to reduced access in laying hens
Bottom line
A new systematic thematic review in Frontiers in Veterinary Science pulls together evidence from 34 empirical studies on keel bone damage in laying hens and how it relates to access to housing areas and functional resources. The review found the clearest pattern around elevated structures: hens with keel fractures were less likely to access perches and other raised resources, moved more cautiously, and made fewer vertical transitions. At the same time, the authors caution that time spent on a perch or in a nest doesn't necessarily mean access is unimpaired, because affected birds may reach those spaces less often but stay there longer once there. The review covered studies published from 2006 to 2026 and concludes that evidence for feeders, drinkers, litter, floor areas, outdoor ranges, popholes, and wintergardens remains sparse or inconsistent. (frontiersin.org)
Why it matters: For veterinary professionals working in poultry health and welfare, the paper sharpens an important distinction between occupancy and access. Keel bone damage is already recognized as a major welfare issue in commercial layers, with prior reviews and sector experts linking it to pain, impaired mobility, and production effects. This new synthesis suggests that when clinicians, auditors, or production teams assess hen behavior in aviary or cage-free systems, simply observing birds on perches or in nests may miss underlying access problems, especially where vertical movement is required. (wpsa.fr)
What to watch: The next step is whether future longitudinal, bird-level studies can clarify cause and effect, and whether housing design, perch layout, genetics, or management changes measurably reduce access-related limitations in hens with keel bone damage. (frontiersin.org)
A new review article in Frontiers in Veterinary Science adds nuance to one of the poultry sector’s most persistent welfare problems: keel bone damage in laying hens. Reviewing 34 empirical studies published between 2006 and 2026, the authors found that keel bone damage was most consistently linked to reduced use of elevated resources and housing areas, including perches and other structures that require vertical movement. Hens with fractures often accessed these areas less frequently, descended more slowly, or made fewer vertical transitions. (frontiersin.org)
That matters because keel bone damage has been under scrutiny for years as a high-priority welfare issue across commercial housing systems. Earlier reviews concluded that the condition is widespread in both caged and non-caged flocks and is associated with behavioral and clinical indicators of reduced welfare. A World’s Poultry Congress review described keel bone damage as a major welfare and production problem, noting that prevalence is typically above 50% by the end of lay, while EFSA’s 2023 scientific opinion identified bone lesions as a highly relevant welfare consequence in laying hens across collective cages and multi-tier systems. (frontiersin.org)
The new paper’s main contribution is methodological as much as biological. The authors screened 345 records, assessed 50 full-text reports, and ultimately included 34 studies. Because the evidence base was heterogeneous, they used a narrative synthesis rather than meta-analysis. Their central conclusion is that resource occupancy and resource access shouldn’t be treated as interchangeable. In other words, a hen seen resting on a perch or occupying a nest box may still have impaired access if she reaches that location less often, more slowly, or with greater difficulty than unaffected birds. Evidence for feeders, drinkers, outdoor areas, and ground-level resources was limited and inconsistent, and few studies could determine whether altered behavior came before or after the onset of keel bone damage. (frontiersin.org)
That finding fits with the broader literature on function and welfare. Earlier work has tied keel bone fractures to pain-related behavior, reduced mobility, and changes in production parameters, while more recent studies continue to frame the condition as a multifactorial problem involving bone quality, housing design, collisions, and sustained egg production pressure. Industry and academic reviews have also emphasized that the problem is unlikely to have a single fix, with interventions likely needing to span genetics, nutrition, rearing, and physical environment. (pubmed.ncbi.nlm.nih.gov)
While this review does not offer a new intervention trial, it does help explain why some welfare assessments may under-detect functional impairment. If affected hens compensate by remaining longer in desirable locations once they get there, snapshot observations could overestimate how accessible those resources really are. That has practical implications for veterinarians advising on aviary design, perch placement, ramp use, stocking density, and monitoring protocols, particularly in systems where hens must navigate height differences repeatedly through the day. (frontiersin.org)
Why it matters: For poultry veterinarians and technical teams, the paper reinforces that keel bone damage is not just a lesion to score at flock checks or depopulation. It may change how hens interact with the environment in ways that affect welfare, behavior, and potentially production, especially in cage-free and multi-tier systems built around vertical movement. The review also supports a more careful reading of behavioral data: perch use alone is an incomplete metric if it doesn’t distinguish attempted access, successful access, time to descend, and frequency of transitions. (frontiersin.org)
What to watch: The authors call for longitudinal, individual-level studies that separate access, occupancy, and departure, ideally using automated tracking plus direct observation. That next wave of research could be important for both welfare science and commercial practice, because it may help identify whether housing redesign, better pullet training for navigation, selective breeding for skeletal integrity, or other management changes can reduce the functional consequences of keel bone damage before the end of lay. (frontiersin.org)