Explanations for keel bone fractures in laying hens: are there explanations in addition to elevated egg production?

Abstract

The current article served to provide the most up-to-date information regarding the causes of keel bone fracture. Although elevated and sustained egg production is likely a major contributing factor toward fractures, new information resulting from the development of novel methodologies suggests complementary causes that should be investigated. We identified 4 broad areas that could explain variation and increased fractures independent of or complementing elevated and sustained egg production: the age at first egg, late ossification of the keel, predisposing bone diseases, and inactivity leading to poor bone health. We also specified several topics that future research should target, which include continued efforts to link egg production and bone health, examination of noncommercial aves and traditional breeds, manipulating of age at first egg, a detailed histological and structural analysis of the keel, assessment of prefracture bone condition, and the relationship between individual activity patterns and bone health.

Prevalence of Keel Bone Damage in Red Jungle Fowls (Gallus gallus)—A Pilot Study

“…The low number of KBF observed is in contrast to the high prevalence, ranging from 30 to 97%, reported in modern laying hens in previous studies [ 2 , 3 , 4 ]. Several of the factors associated with keel bone fractures in previous studies are linked to egg production, e.g., number of eggs and onset of lay [ 20 ]. Therefore, it was no surprise that all the 17 roosters had normal keels without fractures.…”

“…Deviations are linked to pressure on the keel from perching [ 6 ]. The causative factors for KBF are not as clear [ 20 ]. Different explanations have been suggested: Trauma due to collisions within the housing system [ 21 ], genetic susceptibility [ 22 , 23 ], selection for high egg production [ 23 ], bone fragility [ 24 ], early onset of lay [ 4 ], and late ossification of the caudal part of the keel making it vulnerable during egg production [ 18 ].…”

Perch Positioning Affects both Laying Hen Locomotion and Forces Experienced at the Keel

“…On the other hand, forces applied to the keel during controlled movements between perches as observed in the present study are less likely to cause trauma-related fractures, although could contribute to fatigue fractures which occur when normal bone is exposed to repeated stress [ 15 ]. Supporting this position, recent information has suggested that fractures could result from events other than trauma-related collisions (reviewed by [ 33 ]). Casey-Trott et al [ 34 ] suggested that greenstick fractures (i.e., incomplete, bending fractures commonly found in developing bone) might result from routine behaviors, while Harlander-Matauschek et al [ 6 ] specified the need to investigate low energy non-collision events as a cause of fracture.…”

“…As a result of the spatial distribution of resources in aviary systems, hens cannot avoid applying repeated load on their keel bones when using their flight muscles [ 36 ], and thus have to expose their keel to accumulated forces and corresponding risk for stress fractures when accessing feed, water, nest boxes, perches, or litter. Whereas these forces might not be problematic in healthy hens, weakened bones due to high egg laying rates [ 37 ] or other disease conditions [ 33 ] would contribute to increased fracture susceptibility and the risk for insufficiency fractures (when stress is applied to a bone with deficient elastic resistance [ 16 ]). Second, we found that hens responded differently to perch positioning depending on strain (i.e., brown vs. white hens).…”

Managing Free-Range Laying Hens—Part B: Early Range Users Have More Pathology Findings at the End of Lay but Have a Significantly Higher Chance of Survival—An Indicative Study

“…Reasons for this may include that either keel bone damage could have been present at the time of hen placement (obtained in the rearing facilities), occurred within the first few weeks of placement before hens were allowed to access the range, or occurs regardless range utility given the fact that all hens use the aviary system for some time during the day [ 61 ]. Furthermore, keel bone damage may be unrelated to landing impact rather representing greenstick fractures as well as being associated with calcium metabolism, which might have affected all hens of the investigated flock equally [ 62 ]. The results of the present study indicate that range access has no additional benefit in preventing keel bone damage and that modification of the aviary system such as the use of soft perches or terrace-designed aviaries may currently provide the best approach for reducing/preventing keel bone damage [ 59 ].…”