A high prevalence of deviations and fractures of the keel bone is a widespread welfare problem in laying hens. The aim of this study was to experimentally investigate this multifactorial problem throughout the laying period and to compare the prevalence and severity in different layer lines and different housing systems. High performing white (WLA) and brown (BLA) pure bred layer lines and low performing white (R11, G11) and brown layer lines (L68) were kept in both single cages and a floor housing system. A total of 97 hens (19 or 20 from each line, respectively) were repeatedly radiographed in the 35th, 51st and 72nd week of age. Fracture prevalence increased with age (p<0.001). The proportion of deviated keel bone area increased only for caged BLA, WLA and R11 hens (p<0.05) and was significantly higher for caged WLA and R11 hens compared to floor-housed WLA and R11 hens in the 72nd week of age (p<0.05). In the 72nd week of age hens in the floor housing system showed significantly more fractures than hens kept in cages (p<0.05). Prevalence of keel bone deviations was significantly higher in the white layer line R11 but significantly lower in the white layer line G11 compared to both brown layer lines and WLA (p<0.05). Brown layers showed significantly more fractures than white layers (p<0.05) in the 51st and 72nd week of age. Within the brown layers there was a significantly lower prevalence of deviations (p<0.05) and fractures (p<0.05) in the low performing (L68) compared to the high performing line (BLA). Our results show a different development of keel bone damage in caged compared to floor-housed hens under experimental conditions. Additionally, they indicate genetic effects on keel bone damage.

Keel bone fractures and deviations belong to the most severe animal welfare problems in laying hens and are influenced by several factors such as husbandry system and genetic background. It is likely that egg production also influences keel bone health due to the high demand of calcium for the eggshell, which is, in part, taken from the skeleton. The high estrogen plasma concentration, which is linked to the high laying performance, may also affect the keel bone as sexual steroids have been shown to influence bone health. The aim of this study was to investigate the relationship between egg production, genetically determined high laying performance, estradiol-17ß concentration, and keel bone characteristics. Two hundred hens of two layer lines differing in laying performance (WLA: high performing; G11: low performing) were divided into four treatment groups: Group S received an implant containing a GnRH agonist that suppressed egg production, group E received an implant containing the sexual steroid estradiol-17ß, group SE received both implants, and group C were kept as control hens. Between the 12th and the 62nd weeks of age, the keel bone of all hens was radiographed and estradiol-17ß plasma concentration was assessed at regular intervals. Non-egg laying hens showed a lower risk of keel bone fracture and a higher radiographic density compared to egg laying hens. Exogenous estradiol-17ß was associated with a moderately higher risk of fracture within egg laying but with a lower risk of fracture and a higher radiographic density within non-egg laying hens. The high performing layer line WLA showed a significantly higher fracture risk but also a higher radiographic density compared to the low performing layer line G11. In contrast, neither the risk nor the severity of deviations were unambiguously influenced by egg production or layer line. We assume that within a layer line, there is a strong association between egg production and keel bone fractures, and, possibly, bone mineral density, but not between egg production and deviations. Moreover, our results confirm that genetic background influences fracture prevalence and indicate that the selection for high laying performance may negatively influence keel bone health.

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.

The aim of this study was to develop an animal model with non-laying hens which would allow for investigation of the relationship between egg production and common diseases in hens. A total of 40 Lohmann Selected Leghorn hens were kept for 20 weeks in a floor housing system in two groups: group “Adult” (21 weeks of age) and group “Juvenile” (14 weeks of age). In each group, 10 hens were administered a 4.7 mg sustained release deslorelin acetate implant subcutaneously; in group “Adult” after, in group “Juvenile” before the onset of lay. In both groups, the remaining hens served as control hens. An examination of each hen was performed weekly, including ultrasonography to check for ovarian follicles, analysis of estradiol-17ß plasma concentration, and assessment of comb size. Digital radiographs of the keel bone were taken in experimental weeks 7 and 15. No follicles were detected on the ovary of treated hens for a certain time period which varied between individuals (between 8 weeks and until the end of the experiment). Estradiol-17ß concentrations were significantly higher in control hens. The comb was significantly smaller in treated hens. A lower prevalence of keel bone damage (group “Adult”) and foot pad dermatitis (FPD) (both groups) was found in treated compared to control hens. These results show that a model with laying and non-laying hens can be achieved by administering a deslorelin acetate implant. Furthermore, they indicate a relationship between egg production and keel bone damage as well as FPD.

Within the European Union, dustbathing material in cage-housing systems for laying hens became compulsory in 2012. In practice, most producers use food particles as litter substrate. The feed is dropped in small amounts on scratching mats by an automatic transporting system. However, because dustbathing behavior is meant to remove stale lipids from hens' plumage, food particles may not be a suitable substrate due to their fat content. This study analyzes feather lipid concentration (FLC) of laying hens with access to food particles (F) or lignocellulose (L) as litter substrates. In each of 2 identical trials, 84 laying hens of 2 genotypes (Lohmann Selected Leghorn, Lohmann Brown) were kept in 12 compartments (7 hens each). Compartments were equipped with a grid floor and additionally contained a closed dustbathing tray holding F or L. Feather samples (150 feathers) were taken 2 times throughout the experiment. At 23 wk of age, 4 hens per compartment were sampled after they were allowed pair-wise access to a dustbath for 2.5 h and 3 hens were sampled without access to a dustbathing tray (control). After 10 wk of free access to the dustbathing trays, all hens were sampled again. In trial 2, an additional third sampling was made after dustbaths had been closed again for 6 wk. Here, 6 hens per compartment were sampled immediately before and after a dustbath. Dustbathing in F resulted in higher FLC compared with L and control (P < 0.001), whereas no significant difference was found between L and control (P = 0.103). When open access to litter was provided, hens had higher FLC in F compared with L (P < 0.001). The FLC immediately after dustbathing in F was higher compared with the level before dustbathing (P < 0.001), whereas it was lower after dustbathing in L (P = 0.006). These results show that F are not suitable litter material for laying hens because they lead to lipid accumulation on the plumage.