Document type: scientific synthesis published in Frontiers in Veterinary Science
Authors: Stefanie Petow, Helen Louton, Serge Alindekon
Abstract in French (translation): Sternal lesions and access to functional resources and resting areas in laying hens: a systematic thematic review
Sternal lesions (SL) are a major welfare issue in laying hens; however, data regarding their relationship to access to and use of functional resources and housing areas have not been the subject of a systematic review. This review examined the associations between CL and perches, resting areas, nests, feeders, waterers, litter and floor surfaces, outdoor runs, exit hatches, winter gardens, and other defined housing areas. Searches were conducted in PubMed and Web of Science to identify empirical studies published between 2006 and 2026 involving laying hens that assessed keel bone lesions and reported relevant findings related to resources or spaces. Of the 345 references identified, 233 were retained after deduplication. Following a selection based on titles and abstracts, 50 reports underwent full-text evaluation, of which 17 were excluded; one additional study was identified manually, resulting in a total of 34 included studies. Due to significant variations among housing systems, methods for assessing perching behavior, outcome measures, and study timelines, the results were synthesized narratively by resource category and direction of association. The evidence base was limited and unevenly distributed, with most studies focusing on perches, elevated structures, and resting areas. Hens with sternum fractures often accessed elevated resources less frequently, descended more slowly, or made fewer vertical transitions. However, this reduced access did not always correspond to lower occupancy, as some affected hens remained on perches or in nests longer once they reached those locations. Data regarding feeders, waterers, outdoor areas, and ground-level resources were scarce and inconsistent. Few studies determined whether changes in resource use preceded or followed LB, which limits any causal interpretation. Overall, LB was more consistently associated with the use of physically demanding elevated resources, while data regarding other functional areas remained uncertain. Resource occupation should not be interpreted as unlimited access, as affected hens may reach a resource less frequently while remaining there longer. Future studies should use individual-level longitudinal protocols, distinguish between access, occupation, and departure, and combine automated monitoring with direct behavioral observation.
Preview: Keel bone damage (KBD) is a major welfare concern in laying hens; however, evidence on its relationship with access to and use of functional resources and housing areas has not been systematically synthesised. This review examined associations between KBD and perches, resting locations, nests, feeders, drinkers, litter and floor areas, outdoor ranges, popholes, wintergardens, and other defined housing areas. PubMed and Web of Science were searched for empirical studies published between 2006 and 2026 involving laying hens, assessing KBD, and reporting relevant resource- or area-related outcomes. Of 345 records identified, 233 remained after deduplication. Following title and abstract screening, 50 reports underwent full-text assessment, of which 17 were excluded; one additional study was identified manually, yielding 34 included studies. Owing to substantial variation among housing systems, KBD assessment methods, outcome measures, and temporal designs, the findings were synthesised narratively by resource category and direction of association. The evidence base was limited and unevenly distributed, with most studies focusing on perches, elevated structures, and resting locations. Hens with keel fractures often accessed elevated resources less frequently, descended more slowly, or made fewer vertical transitions. However, reduced access did not always correspond to reduced occupancy, as some affected hens remained longer on perches or in nests once these locations had been reached. Evidence for feeders, drinkers, outdoor areas, and ground-level resources was sparse and inconsistent. Few studies established whether changes in resource use preceded or followed KBD, limiting causal interpretation. Overall, KBD was most consistently associated with the use of physically demanding elevated resources, while evidence for other functional areas remained uncertain. Resource occupancy should not be interpreted as unrestricted access because affected hens may reach a resource less often yet remain there longer. Future studies should use longitudinal individual-level designs, distinguish access from occupancy and departure, and combine automated tracking with direct behavioural observation.
