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Keel bone fractures and deviations are one of the major welfare and health issues in commercial laying hens. In non-cage housing systems like aviaries, falls and collisions with perches and other parts of the housing system are assumed to be one of the main causes for the high incidence of keel bone damage. The objectives of this study were to investigate the effectiveness of a soft perch material to reduce keel bone fractures and deviations in white (Dekalb White) and brown laying hens (ISA Brown) kept in an aviary system under commercial conditions. In half of 20 pens, all hard, metal perches were covered with a soft polyurethane material. Palpation of 20 hens per pen was conducted at 18, 21, 23, 30, 38, 44 and 64 weeks of age. Production data including egg laying rate, floor eggs, mortality and feed consumption were collected over the whole laying period. Feather condition and body mass was assessed twice per laying period. The results revealed that pens with soft perches had a reduced number of keel bone fractures and deviations. Also, an interaction between hybrid and age indicated that the ISA hybrid had more fractured keel bones and fewer non-damaged keel bones compared with the DW hybrid at 18 weeks of age, a response that was reversed at the end of the experiment. This is the first study providing evidence for the effectiveness of a soft perch material within a commercial setting. Due to its compressible material soft perches are likely to absorb kinetic energy occurring during collisions and increase the spread of pressure on the keel bone during perching, providing a mechanism to reduce keel bone fractures and deviations, respectively. In combination with genetic selection for more resilient bones and new housing design, perch material is a promising tool to reduce keel bone damage in commercial systems.

The goal of this study was to evaluate the prevalence of keel bone deformities of laying hens in Switzerland. The keel bones of 100 end-of-lay hens from each of 39 flocks (3900 in total) were palpated. On average, 25·4% of the hens had moderately or severely deformed keel bones and the overall prevalence including slight deformities was 55%. 3. Variation between flocks was considerable. Thus, the prevalence of moderately or severely deformed keel bones ranged from 6 to 48%, and the overall prevalence including slight deformities ranged from 20 to 83%. Aviary housing was associated with a higher prevalence of total, and severe or moderate deformations, compared with floor pens. There were no significant differences in the number of deformities between the different plumage colours, hybrids or perch materials.

Simple SummaryNumerous studies have documented a high prevalence of keel bone fractures in laying hens. In this longitudinal study, 80 white and brown laying hens were regularly checked for keel bone deviations and fractures while egg production was individually monitored. About 62% of the hens had broken keel bones at depopulation. More new fractures occurred during the time when laying rates were highest. Hens with broken keel bones at depopulation had laid their first egg earlier than hens with intact keel bones. All birds with bumblefoot on both feet had a fracture at depopulation.AbstractNumerous studies have demonstrated influences of hybrid, feed, and housing on prevalence of keel bone fractures, but influences of behavior and production on an individual level are less known. In this longitudinal study, 80 white and brown laying hens were regularly checked for keel bone deviations and fractures while egg production was individually monitored using Radio Frequency Identification (RFID) from production until depopulation at 65 weeks of age. These focal birds were kept in eight pens with 20 hens per pen in total. About 62% of the hens had broken keel bones at depopulation. The occurrence of new fractures was temporally linked to egg laying: more new fractures occurred during the time when laying rates were highest. Hens with fractured keel bones at depopulation had laid their first egg earlier than hens with intact keel bones. However, the total number of eggs was neither correlated with the onset of egg laying nor with keel bone fractures. All birds with bumblefoot on both feet had a fracture at depopulation. Hens stayed in the nest for a longer time during egg laying during the ten days after the fracture than during the ten days before the fracture. In conclusion, a relationship between laying rates and keel bone fractures seems likely.

A systematic review of investigations on productivity, mortality and cannibalism of laying hens housed in aviaries is presented. In Part One we reviewed the studies that compared these parameters between laying hens housed in aviaries and in conventional cages. In Part Two we investigated the relative impact of strain, beak trimming and rearing condition on productivity and mortality in aviaries. The comparative analysis revealed that aviary hens consumed 3.0 % more food than caged hens, and food conversion was 6.7 % higher in aviaries than in cages. On the other hand, the mortality rate and cannibalism rate did not differ significantly between the two housing systems. The analysis of causes of variation in productivity, mortality rate and cannibalism rate in aviaries revealed a strong effect of strain. Beak trimming was associated with a reduced prevalence of cannibalism rates but had no effect on overall mortality. It also reduced egg weight and food consumption. Early access to litter during the rearing period had a positive effect on egg weight; egg mass, food conversion and mortality rate. In conclusion, we found a slightly reduced productivity of aviaries in relation to cages although the mortality rates and the prevalence of cannibalism did not differ between these housing systems. To further improve productivity and reduce mortality of hens housed in aviaries we recommend the choice of suitable strains and the implementation of improved rearing conditions including early access to litter. Keywords: systematic review; laying hens; aviary; housing system; productivity; mortality; strain; beak trimming; rearing IntroductionThe aviary housing system for laying hens was developed as an alternative to conventional battery cages. In various countries, this new housing system has been assessed with regard to animal welfare health and economic aspects, and these investigations often compared various parameters between hens housed in aviaries and conventional cages. To draw general conclusions, however, each of these studies was neither large enough nor covered a sufficiently wide range of conditions. We therefore made a systematic and quantitative review in which we combined the independent results of these studies. The aim of a systematic review is to produce an up-to-date and reproducible account of the present state of research. Moreover, according to Gates (2002), a quantitative review provides a considerable advance in scientific rigour over traditional narrative or "vote-counting" reviews.An early type of aviary was already operating in 1979 (Fölsch et al., 1983) and since then, the system was further developed. One of the aviary's best features is the construction of tiers and perches above the littered area, which allows the hens to move and get out of the way both horizontally and vertically. Furthermore, the spatial separation of the areas for eating, drinking, resting, foraging and dust bathing is considered as advantageous (Fröhlich, 1995). The use of the third dimension allows for housing additional...

Several studies have shown a high prevalence of keel bone deformities in commercial laying hens. The aim of this project was to assess the effects of perch material, a vitamin D feed additive (25-hydroxyvitamin D(3); HyD, DSM Nutritional Products, Basel, Switzerland), and genetics on keel bone pathology. The study consisted of 2 experiments. In the first experiment, 4,000 Lohmann Selected Leghorn hens were raised in aviary systems until 18 wk of age. Two factors were investigated: perch material (plastic or rubber-coated metal) and feed (with and without HyD). Afterward, the hens were moved to a layer house with 8 pens with 2 aviary systems. Daily feed consumption, egg production, mortality, and feather condition were evaluated. Every 6 wk, the keel bones of 10 randomly selected birds per pen were palpated and scored. In the second experiment, 2,000 Lohmann Brown (LB) hens and 2,000 Lohmann Brown parent stock (LBPS) hens were raised in a manner identical to the first experiment. During the laying period, the hens were kept in 24 identical floor pens but equipped with different perch material (plastic or rubber-coated metal). The same variables were investigated as in the first experiment. No keel bone deformities were found during the rearing period in either experiment. During the laying period, deformities gradually appeared and reached a prevalence of 35% in the first experiment and 43.8% in the second experiment at the age of 65 and 62 wk, respectively. In the first experiment, neither HyD nor the aviary system had any significant effect on the prevalence of keel bone deformities. In the second experiment, LBPS had significantly fewer moderate and severe deformities than LB, and rubber-coated metal perches were associated with a higher prevalence of keel bone deformities compared with plastic perches. The LBPS laid more but smaller eggs than the LB. Again, HyD did not affect the prevalence of keel bone deformities. However, the significant effect of breed affiliation strongly indicates a sizeable genetic component that may provide a basis for targeted selection.

The prevalence of keel bone damage as well as external egg parameters of 2 pure lines divergently selected for high (H) and low (L) bone strength were investigated in 2 aviary systems under commercial conditions. A standard LSL hybrid was used as a reference group. Birds were kept mixed per genetic line (77 hens of the H and L line and 201 or 206 hens of the LSL line, respectively, per pen) in 8 pens of 2 aviary systems differing in design. Keel bone status and body mass of 20 focal hens per line and pen were assessed at 17, 18, 23, 30, 36, 43, 52, and 63 wk of age. External egg parameters (i.e., egg mass, eggshell breaking strength, thickness, and mass) were measured using 10 eggs per line at both 38 and 57 wk of age. Body parameters (i.e. tarsus and third primary wing feather length to calculate index of wing loading) were recorded at 38 wk of age and mortality per genetic line throughout the laying cycle. Bone mineral density (BMD) of 15 keel bones per genetic line was measured after slaughter to confirm assignment of the experimental lines. We found a greater BMD in the H compared with the L and LSL lines. Fewer keel bone fractures and deviations, a poorer external egg quality, as well as a lower index of wing loading were found in the H compared with the L line. Mortality was lower and production parameters (e.g., laying performance) were higher in the LSL line compared with the 2 experimental lines. Aviary design affected prevalence of keel bone damage, body mass, and mortality. We conclude that selection of specific bone traits associated with bone strength as well as the related differences in body morphology (i.e., lower index of wing loading) have potential to reduce keel bone damage in commercial settings. Also, the housing environment (i.e., aviary design) may have additive effects.