Effect of housing birds in cages or an aviary system on bone characteristics

Breed and loading history influence in vivo skeletal strain patterns in pre-pubertal female chickens

The influence of loading history on in vivo strains within a given specie remains poorly understood, and although in vivo strains have been measured at the hindlimb bones of various species, strains engendered during modes of activity other than locomotion are lacking, particularly in non-human species. For commercial egg-laying chickens specifically, there is an interest in understanding their bones' mechanical behaviour, particularly during youth, to develop early interventions to prevent the high incidence of osteoporosis in this population. We measured in vivo mechanical strains at the tibiotarsus midshaft during steady activities (ground, uphill, downhill locomotion) and non-steady activities (perching, jumping, aerial transition landing) in 48 pre-pubescent female (egg-laying) chickens from two breeds that were reared in three different housing systems, allowing varying amounts and types of physical activity. Mechanical strain patterns differed between breeds, and were dependent on the activity performed. Mechanical strains were also affected by rearing environment: chickens that were restricted from performing dynamic load bearing activity due to caged-housing generally exhibited higher mechanical strain levels during steady, but not non-steady activities, compared to chickens with prior dynamic load-bearing activity experience. Among chickens with prior experience of dynamic load bearing activity, those reared in housing systems that allowed more frequent physical activity did not exhibit lower mechanical strains. In all groups, the tibiotarsus was subjected to a loading environment consisting of a combination of axial compression, bending, and torsion, with torsion being the predominant source of strain. Aerial transition landing produced the highest strain levels with unusual strain patterns compared to other activities, suggesting it may produce the strongest anabolic response. These results exemplify how different breeds within a given specie adapt to maintain different patterns of mechanical strains, and how benefits of physical activity in terms of resistance to strain are activity-type dependent and do not necessarily increase with increased physical activity. These findings directly inform controlled loading experiments aimed at studying the bone mechanoresponse in young female chickens and can also be associated to measures of bone morphology and material properties to understand how these features influence bone mechanical properties in vivo.

Untargeted metabolomics reveals the effect of rearing systems on bone quality parameters in chickens

The objective of this study was to investigate the effects of rearing systems on the bone quality parameters in chickens using a metabolomics strategy. A total of 419 male one-day-old chicks were randomly allocated to two groups, a floor rearing group (FRG, n = 173) and a cage rearing group (CRG, n = 246). At 6, 8, 10, and 12 weeks of age, all chickens were radiographed by a digital X-ray machine, and body weight was recorded. At 12 weeks of age, 12 birds were selected from each group to obtain tibia and femur, and bone quality parameters of bone mineral density (BMD), mineral content (BMC), breaking strength (BBS), stiffness, Young's modulus (YM), ash content, calcium content, and phosphorus content were determined. An untargeted metabolomics assay was performed to identify changes in the serum metabolic profile (n = 8 birds/group). The results showed that cage-reared chickens had wider tibiae and greater body weight compared with floor-reared chickens. There were no significant differences in BMC or BBS between the two groups (p > 0.05), but BMD, ash content, calcium content, and phosphorus content of the tibia and femur of FRG were significantly higher than those of CRG (p < 0.05). Greater stiffness and YM of the femur were also observed in birds raised in the FRG compared with those raised in the CRG (p < 0.05). Taken together, the results suggest that rearing systems affected bone quality parameters. Furthermore, 148 and 149 differential metabolites were identified in positive and negative ion modes by LC-MS/MS analysis, among which 257 metabolites were significantly correlated with 16 bone quality parameters, including leucine, myristoleic acid, glycocholic acid, and N-phenylacetamide. KEGG analysis indicated that 15 metabolic pathways, including six pathways of amino acid metabolism, two pathways of lipid metabolism, and two pathways of carbohydrate metabolism, were responsible for bone quality. Overall, the present study demonstrated the effect of rearing systems on bone quality parameters, and identified several metabolites and metabolic pathways associated with bone quality parameters.

Genetics of tibia bone properties of crossbred commercial laying hens in different housing systems

Osteoporosis and bone fractures are a severe problem for the welfare of laying hens, with genetics and environment, such as housing system, each making substantial contributions to bone strength. In this work, we performed genetic analyses of bone strength, bone mineral density, and bone composition, as well as body weight, in 860 commercial crossbred laying hens from 2 different companies, kept in either furnished cages or floor pens. We compared bone traits between housing systems and crossbreds and performed a genome-wide association study of bone properties and body weight. As expected, the 2 housing systems produced a large difference in bone strength, with layers housed in floor pens having stronger bones. These differences were accompanied by differences in bone geometry, mineralization, and chemical composition. Genome scans either combining or independently analyzing the 2 housing systems revealed no genome-wide significant loci for bone breaking strength. We detected 3 loci for body weight that were shared between the housing systems on chromosomes 4, 6, and 27 (either genome-wide significant or suggestive) and these coincide with associations for bone length. In summary, we found substantial differences in bone strength, content, and composition between hens kept in floor pens and furnished cages that could be attributed to greater physical activity in pen housing. We found little evidence for large-effect loci for bone strength in commercial crossbred hens, consistent with a highly polygenic architecture for bone strength in the production environment. The lack of consistent genetic associations between housing systems in combination with the differences in bone phenotypes could be due to gene-by-environment interactions with housing system or a lack of power to detect shared associations for bone strength.

Laying hens under smallholder conditions: laying performance, growth and bone quality of tibia and femur including essential elements

The study aimed to assess laying performance, growth rate, and bone quality properties of tibia and femur bones of various genotypes of laying hens, including determining essential element composition at the end of the laying cycle in smallholder conditions. The study included three genotypes of laying hens; Czech golden spotted (CGS), White Leghorn (LE) and Dominant Partridge D300 (D300) hens. In total, 180 hens (60/genotype) were used in 3 replications (20 hens/replication). The eggs were collected to determine egg lay and hen-day egg production. Additionally, feed consumption was recorded to determine feed consumption per day or egg, resp. The mortality rate was recorded. Hens were individually weighed every 10 wk to analyze the growth performance and body weight changes during the laying cycle. The differences in performance characteristics were observed as significant in all studied parameters. The bone quality analysis consisted of the determination of bone weight, length, width, and fracture toughness. Furthermore, dry matter, ash, and selected elements, which included boron (B), calcium (Ca), cadmium (Cd), copper (Cu), iron (Fe), magnesium (Mg), manganese (Mn), sodium (Na), phosphorus (P), lead (Pb), and zinc (Zn) were assessed. Regarding the results of tibia and femur bones, the effect of genotype was determined as significant in all evaluated properties. In terms of element composition, all evaluated elements significantly differed among the genotypes in the tibia (with one exception of Cu) and in the femur (with one exception of Cd). In conclusion, our results showed that hens’ performance, production quality, mortality and bone properties significantly differed among genotypes under smallholder conditions. Thus, every genotype needs to be carefully considered, when the rearing conditions are set.

Untargeted metabolomics study on the effects of rearing ducks in cages on bone quality

The cage rearing model of the modern poultry industry makes the bones of birds more vulnerable to deterioration. In this study, at 8 wk of age, a total of 60 birds were randomly allocated to 2 groups, including the floor rearing group (FRD) and cage rearing group (CRD), and their body weight was measured every 2 wk. At the age of 20 wk, the tibia, femur, and humerus were collected from each group (n = 12) to determine the bone quality parameters such as weight, size, bone mineral density (BMD), breaking strength, cortical thickness, and area, ash content, calcium (Ca) content, and phosphorus (P) content. Meanwhile, the serum metabolome composition of both groups was detected by untargeted metabolome technology. The results showed that there were no significant differences in body weight, bone weight, and size between the 2 groups (P > 0.05), but the humerus mineral density and the breaking strength, cortical bone thickness, cortical bone area percentage of tibia, femur, and humerus of CRD was significantly lower than those of FRD (P < 0.05), indicating that the cage rearing system caused the deterioration of bone quality. Based on nontarget metabolomics, 49 metabolites were correlated with bone quality parameters, and 10 key metabolites were strongly correlated, including erucic acid, citric acid, and ketoleucine. In addition, the KEGG analysis showed that the caged system mainly perturbed amino acid metabolism, lipid metabolism, and energy metabolism, which led to changes in related metabolite levels, produced ROS, and altering energy supply, thus leading to a deterioration of bone quality of cage rearing ducks. Therefore, our findings were helpful to further understand the potential mechanism of the deterioration of duck bone quality in cage rearing system, provided a theoretical basis for reducing the occurrence of poultry osteoporosis, and ensuring the healthy development of poultry breeding.

The effect of light intensity on the body weight, keel bone quality, tibia bone strength, and mortality of brown and white feathered egg-strain pullets reared in perchery systems

The development of the musculoskeletal system is influenced by bird activity, which can be impacted by light intensity (L). The objective of this study was to determine the effect of L on the growth and bone health of Lohmann Brown-Lite (LB) and Lohmann LSL-Lite (LW) pullets. Three L treatments (10, 30 or 50 lux, provided by white LED lights) were used in a Randomized Complete Block Design in 2 repeated trials. LB and LW (n = 1,800 per strain [S]) were randomly assigned to floor pens (50 pullets per pen; 12 pen replicates per L × S) within 6 light-tight rooms from 0 to 16 wk. Each pen contained 4 parallel perches and a ramp. Data collected include cumulative mortality, BW at 0, 8, and 16 wk, and uniformity, keel bone damage (KBD; deviations, fractures), breast muscle weight, and tibiae bone strength at 16 wk. Tibiae bone resistance to mechanical stress was assessed using a three-point-bending test. The effect of L, S, and their interactions were analyzed using Proc Mixed (SAS 9.4) and differences were considered significant when P < 0.05. L did not affect BW, KBD, or mortality. An interaction between L and S was observed for bone stress (bone strength relative to bone size), however, in general, LW pullets had greater resistance to bone stress (peak noted at 30 lux) than LB (peak at 50 lux). LB pullets were heavier than LW at 8 and 16 wk. There were no S differences on KBD from palpated or dissected keel bones. LB pullets had higher breast muscle weight and heavier tibiae than LW, however relative to BW, LW had a higher percentage of breast muscle and a longer and thicker tibiae than LB. LW had higher mortality during the first wk but there was no relationship to L. Conclusively, the results suggest that L, within a range of 10 to 50 lux, does not affect pullet BW or KBD, however S may affect both parameters, as well as bone strength.

Comparative analysis of the morphology, chemistry and structure of the tibiotarsus, humerus and keel bones in laying hens

1. Bone properties are adapted to their specific functions in the animal, so various types of bones develop different characteristics depending on their location in the skeleton.2. The aim of this research was to compare the chemical composition, mineral characteristics and structural organisation in tibiotarsus, humerus and keel bones as representatives of hen skeletal mineralisation. Complementary analytical techniques, such as X-ray radiography, optical and electron microscopy, thermogravimetry and 2D X-ray diffraction, were used for characterisation.3. The humerus had a thinner cortex and cortical bone mineral had higher crystallinity and a greater degree of crystal orientation than the tibiotarsus. The humerus generally lacks medullary bone although, when present, it has a higher mineral content than seen in the tibiotarsus. These differences were attributed to the different forces that stimulate bone formation and remodelling.4. The keel cortical bone had a lower degree of mineralisation than the tibiotarsus or humerus. Its degree of mineralisation decreased from the cranial to the distal end of the bone. This gradient may affect keel mechanical properties, making it more prone to deformation and fractures.5. Data from studying different bones in laying hens can help to understand mineralisation as well as finding solutions to prevent osteoporosis-related fractures.

Effects of the housing environment and laying hen strain on tibia and femur bone properties of different laying phases of Hy-Line hens

This study aimed to determine the effect of the housing environment and laying hen strain on tibia and femur properties. A 3 × 2 factorial arrangement of 3 housing environments (conventional cages [CC], enriched colony cages [EC], and free range [FR]) and 2 laying hen strains (Hy-Line W-36 [W-36] and Hy-Line Brown [HB]) in a completely randomized design was conducted from 32 to 85 wk of age. Six left tibias were collected at 8 different time points (38, 45, 52, 59, 65, 72, 79, and 85 wk of age), whereas 6 left femurs were collected at 3 time points (38, 65, and 85 wk of age). Tibias were evaluated for tibia breaking strength (TBS) and ash percentage, whereas femurs were evaluated for bone mineral density (BMD), bone mineral content, bone volume as a fraction tissue volume, and porosity percentage from total, cortical, medullary, and trabecular bones. The higher TBS (P = 0.0005) and ash percentage (P = 0.045) was observed in hens raised in FR systems compared with those raised in the CC. Overall, TBS of W-36 hens was significantly greater than that of HB hens (P < 0.0001); however, there was no difference in the ash percentage between the strains (P > 0.05). An interaction between the housing environment and hen strain was observed for BMD (P = 0.04), wherein W-36 hens raised in the FR system had higher BMD than HB hens. Similarly, hens raised in FR systems had higher trabecular bone volume than those raised in CC (P = 0.022). Hen strain influenced total and cortical bone properties: BMD, bone volume as a fraction tissue volume, and porosity percentage, wherein W-36 hens had better properties than HB hens (P < 0.05). Trabecular BMD was higher in W-36 hens than in HB hens (P = 0.04), whereas bone volume was higher in HB hens (P < 0.0001). The results suggest that raising laying hens in alternative housing systems that have provision for exercise such as FR reduces structural bone loss, stimulate structural bone formation, and improve breaking strength of bones; however, it varies with the strain.

Nutrition, feeding and laying hen welfare

The relationship between nutrition and welfare is usually considered to be a direct result of supplying the hen with adequate quantities of feed and water. This simple notion of freedom from hunger and thirst belies the fact that nutrients play a pivotal role in the body’s response to challenges whether they relate to ambient temperature, gastrointestinal health, pathogen exposure, metabolic disorders, or social and mental stress. In all instances, maintaining homeostasis and allowing for physiologic response is dependent on an adequate and balanced nutrient supply. It is accepted that most laying hens are fed a complete diet, formulated commercially to provide the required nutrients for optimal health, egg production and welfare. In other words, the laying hen, irrespective of her housing, does not experience hunger or thirst. However, despite adequate nutrient and water supply, certain senarios can significantly affect and alter the nutrient requirements of the hen. Furthermore, the chemical composition and also the physical form of feed can significantly contribute to prevent or treat welfare and health conditions and is, therefore, a highly relevant tool to ensure and maintain an adequate welfare status. Therefore, this review takes a broader perspective of nutritional welfare and considers the nutrition of hens managed in different production systems in relation to nutritional physiology, gut microbiota, stress, metabolic disorders and feeding management.

Various bone parameters are positively correlated with hen body weight while range access has no beneficial effect on tibia health of free-range layers

The aim of this study was to determine if body weight or range use has a significant impact on bone health in commercial free-range laying hens, and to correlate tibia bone quality parameters with individual range usage and body weight. A total of 30 Lohmann Brown hens at 74 wk of age were selected from a commercial free-range farm and were either classified as heavy (mean ± SEM body weight 2.11 ± 0.034 kg, n = 14) or light (1.68 ± 0.022 kg, n = 16) body weight, and also classified as rangers (accessed the range for 86.7% of available days, n = 16) or stayers (accessed the range for 5.00% of available days, n = 14). The left tibiae of all individuals were analyzed for morphological parameters using computed tomography, evaluated for bone breaking strength, and ashed to determine mineral composition. Keel bone scoring was performed based on observation. Data were analyzed using a 2 × 2 factorial ANOVA, and regression analysis was performed. There was no measurable effect of range usage on any of the tibia parameters investigated. The body weight was significantly correlated with tibia breaking strength (r = 0.59), tibia weight (r = 0.56), tibia length (r = 0.64), diaphyseal diameter (r = 0.61), and total tibia volume (r = 0.67). In conclusion, range access had no beneficial effect on bone health. The impact of internal hen house furnishing and movement on bone health needs further investigation.

Opportunities for exercise during pullet rearing, Part I: Effect on the musculoskeletal characteristics of pullets

Increased load-bearing exercise improves bone quality characteristics in a variety of species, including laying hens. Providing increased opportunities for exercise during the pullet rearing phase, a period of substantial musculoskeletal growth, offers a proactive approach to reducing osteoporosis by improving bone composition. The main objective of this study was to determine whether differing opportunities for exercise during rearing influences pullet musculoskeletal characteristics. Two flock replicates of 588 Lohmann Selected Leghorn-Lite pullets were reared in either standard, conventional cages (Conv) or an aviary rearing system (Avi) from day-old chicks until 16 wk of age. The keel bone and the muscles and long bones of the wings and legs were collected at 16 wk to measure muscle growth differences between rearing treatments and quantify bone quality characteristics using quantitative computed tomography (QCT) and bone breaking strength (BBS) assessment. Keel bone characteristics and muscle weights were adjusted for BW and analyses for QCT and BBS included BW as a covariate. At 16 wk of age, rearing system had an effect on the majority of keel bone characteristics (P < 0.05). The length of the keel metasternum, caudal tip cartilage length, and the overall percentage of cartilage present on the keel at 16 wk was greater in the Avi pullets compared to the Conv pullets (P < 0.01). Wing and breast muscle weights of the Avi pullets were greater than the Conv pullets (P < 0.001), but leg muscle weights were greater in the Conv pullets (P = 0.026). Avi pullets had greater total bone density, total cross-sectional area, cortical cross-sectional area, total bone mineral content, and cortical bone mineral content than Conv pullets for the radius, humerus, and tibia (P < 0.001). Avi pullets had greater BBS compared to the Conv pullets for the radius, humerus, and tibia (P < 0.01). Increased opportunities for exercise offered by the aviary rearing system increased muscle and bone growth characteristics in pullets at 16 wk of age.

Opportunities for exercise during pullet rearing, Part II: Long-term effects on bone characteristics of adult laying hens at the end-of-lay

Osteoporosis in laying hens has been a production and welfare concern for several decades. The objective of this study was to determine whether differing opportunities for exercise during pullet rearing influences long-term bone quality characteristics in end-of-lay hens. A secondary objective was to assess whether differing opportunities for exercise in adult housing systems alters bone quality characteristics in end-of-lay hens. Four flock replicates of 588 Lohmann Selected Leghorn-Lite pullets were reared in either conventional cages (Conv) or an aviary rearing system (Avi) and placed into conventional cages (CC), 30-bird furnished cages (FC-S), or 60-bird furnished cages (FC-L) for adult housing. Wing and leg bones were collected at the end-of-lay to quantify bone composition and strength using quantitative computed tomography and bone breaking strength (BBS). At the end-of-lay, Avi hens had greater total and cortical cross-sectional area (P < 0.05) for the radius and tibia, greater total bone mineral content of the radius (P < 0.001), and greater tibial cortical bone mineral content (P = 0.029) than the Conv hens; however, total bone mineral density of the radius (P < 0.001) and cortical bone mineral density of the radius and tibia (P < 0.001) were greater in the Conv hens. Hens in the FC-L had greater total bone mineral density for the radius and tibia (P < 0.05) and greater trabecular bone mineral density for the radius (P = 0.027), compared to hens in the FC-S and CC. Total bone mineral content of the tibia (P = 0.030) and cortical bone mineral content of the radius (P = 0.030) and tibia (P = 0.013) were greater in the FC-L compared to the CC. The humerus of Conv hens had greater BBS than the Avi hens (P < 0.001), and the tibiae of FC-L and FC-S hens had greater BBS than CC hens (P = 0.006). Increased opportunities for exercise offered by the aviary rearing system provided improved bone quality characteristics lasting through to the end-of-lay.

The effects of <i>Saccharomyces cerevisiae</i> on the morphological and biomechanical characteristics of the tibiotarsus in broiler chickens

Abstract. The aim of this study is to examine the effects of different levels of the feed supplement Saccharomyces cerevisiae, a yeast metabolite, on broiler tibiotarsus traits and to reduce leg problems by identifying the pathological changes in leg skeletal system. Thus, reducing leg disorders due to the skeletal system, the cause of significant economic losses in our country (Turkey), was investigated by the supplementation of Saccharomyces cerevisiae in broiler feed. In the study, 300 male day-old, Ross 308 broiler chicks were used. Experiment groups were designed as follows: control; 0.1 % Saccharomyces cerevisiae; 0.2 % Saccharomyces cerevisiae; 0.4 % Saccharomyces cerevisiae. The experimental diets were chemically analyzed according to the methods of the Association of Official Analytical Chemists. Twelve groups were obtained, including three replicates for each experimental group. Each replicated group was comprised of 25 chicks, and thus 75 chicks were placed in each experimental group. After 42 days, broiler chickens were slaughtered. Tibiotarsi were weighed with a digital scale, and the lengths were measured with a digital caliper after the drying process. Cortical areas were measured with the ImageJ Image Processing and Analysis Program. A UTEST Model-7014 tension and compression machine and a Maxtest software were used to determine the bone strength of the tibiotarsus. The severity of the tibial dyschondroplasia lesion was evaluated as 0, +1, +2 and +3. Crude ash, calcium and phosphorus analyses were performed to determine the inorganic matter of tibiotarsi. For radiographic evaluations of epiphyseal growth plates, tibiotarsi from the right legs were photographed in lateral and craniocaudal positions and examined. Statistical analyses were performed with the SPSS statistics program. It was observed that the use of Saccharomyces cerevisiae as a feed supplement led to an increase in the bone traits of broiler chickens. Optimum results for bone mineral content, biomechanical traits and strength were provided by the addition of 0.2 % Saccharomyces cerevisiae in broiler feed. As a result, the use of yeast as feed supplements in broilers is considered to be an economic and convenient way of providing animal welfare and preventing commercial losses due to leg problems.

Effects of stock density on the laying performance, blood parameter, corticosterone, litter quality, gas emission and bone mineral density of laying hens in floor pens

The effects of stocking density on the performance, egg quality, leukocyte concentration, blood biochemistry, corticosterone levels, bone mineral density, and noxious gas emission of laying hens were investigated. Eight hundred 34-week-old Hy-Line Brown laying hens (Gallus gallus domesticus) were randomly assigned to one of 4 treatments, each of which was replicated 4 times. Four stocking densities, including 5, 6, 7, and 10 birds/m2, were compared. A commercial-type basal diet was formulated to meet or exceed nutrient recommendations for laying hens from the National Research Council. The diet was fed to the hens ad libitum for 8 wk. Results indicated that hen-day egg production, egg mass, and feed intake were less for (P < 0.01) 10 birds/m2 stock density than other stock densities. Production rate of floor and broken eggs and eggshell strength were greater (P < 0.01) for 10 birds/m2 stock density than other stock densities. There were no significant differences in the level of leukocytes among densities. However, heterophils and the H/L ratio were greater (P < 0.01) for 10 birds/m2 than in stock density of 6 or 7 birds/m2 Serum corticosterone was greater (P < 0.01) 10 birds/m2 than stock density than other stock densities. Litter moisture and gas emission (CO2 and NH3) were greater (P < 0.01) for 10 birds/m2 than stock density than 6 and 7 birds/m2 stock density. Bone mineral content was not influenced by increasing stock density. However, bone mineral density was less (P < 0.05) for 10 m2 stock density than other stock densities. These results indicate that increasing the density beyond 5 birds/m2 elicits some negative effects on laying performance of Hy-Line brown laying hens.

Failed landings after laying hen flight in a commercial aviary over two flock cycles

Many egg producers are adopting alternative housing systems such as aviaries that provide hens a tiered cage and a litter-covered open floor area. This larger, more complex environment permits expression of behaviors not seen in space-limited cages, such as flight. Flight is an exercise important for strengthening bones; but domestic hens might display imperfect flight landings due to poor flight control. To assess the potential implications of open space, we evaluated the landing success of Lohmann white laying hens in a commercial aviary. Video recordings of hens were taken from 4 aviary sections at peak lay, mid lay and end lay across two flock cycles. Observations were made in each focal section of all flights throughout the day noting flight origin and landing location (outer perch or litter) and landing success or failure. In Flock 1, 9.1% of all flights failed and 21% failed in Flock 2. The number of flights decreased across the laying cycle for both flocks. Proportionally more failed landings were observed in the double row sections in Flock 2. Collisions with other hens were more common than slipping on the ground or colliding with aviary structures across sections and flocks. More hens slipped on the ground and collided with physical structures at peak lay for Flock 2 than at other time points. More collisions with other hens were seen at mid and end lay than at peak lay for Flock 2. Landings ending on perches failed more often than landings on litter. These results indicate potential for flight-related hen injuries in aviary systems resulting from failed landings, which may have implications for hen welfare and optimal system design and management.

Prevalence of keel bone deformities in Swiss laying hens

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.

Effects of housing, perches, genetics, and 25-hydroxycholecalciferol on keel bone deformities in laying hens

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.

Hen welfare in different housing systems

Egg production systems have become subject to heightened levels of scrutiny. Multiple factors such as disease, skeletal and foot health, pest and parasite load, behavior, stress, affective states, nutrition, and genetics influence the level of welfare hens experience. Although the need to evaluate the influence of these factors on welfare is recognized, research is still in the early stages. We compared conventional cages, furnished cages, noncage systems, and outdoor systems. Specific attributes of each system are shown to affect welfare, and systems that have similar attributes are affected similarly. For instance, environments in which hens are exposed to litter and soil, such as noncage and outdoor systems, provide a greater opportunity for disease and parasites. The more complex the environment, the more difficult it is to clean, and the larger the group size, the more easily disease and parasites are able to spread. Environments such as conventional cages, which limit movement, can lead to osteoporosis, but environments that have increased complexity, such as noncage systems, expose hens to an increased incidence of bone fractures. More space allows for hens to perform a greater repertoire of behaviors, although some deleterious behaviors such as cannibalism and piling, which results in smothering, can occur in large groups. Less is understood about the stress that each system imposes on the hen, but it appears that each system has its unique challenges. Selective breeding for desired traits such as improved bone strength and decreased feather pecking and cannibalism may help to improve welfare. It appears that no single housing system is ideal from a hen welfare perspective. Although environmental complexity increases behavioral opportunities, it also introduces difficulties in terms of disease and pest control. In addition, environmental complexity can create opportunities for the hens to express behaviors that may be detrimental to their welfare. As a result, any attempt to evaluate the sustainability of a switch to an alternative housing system requires careful consideration of the merits and shortcomings of each housing system.

Providing laying hens with perches: fulfilling behavioural needs but causing injury?

1. The EU laying hen directive, which bans standard battery cages from 2012, has implications for animal welfare, particularly since housing laying hens in extensive systems, while increasing natural behaviour and improving bone strength, is associated with a greater level of bone fractures, predominantly of the keel bone, compared to birds housed in cages. 2. The aetiology and welfare consequences of keel and other bone fractures are not well understood and could have important implications for housing system designs. While proposed alterations to layer housing are based on the desire to fulfil behavioural needs and increase bone strength, there appears to have been little consideration of the effect of system on potential injury. 3. In addition, there are variations in how the directive is interpreted. For example, egg producers housing hens in extensive systems in Scotland and Northern Ireland must provide hens with aerial perches, whereas in England and Wales they do not. Aerial perches may be implicated in bone fracture injuries. 4. This paper reviews the prevalence of bone fractures in the egg-laying sector of the poultry industry and the literature on perches. It also explores how bone fractures may be occurring. 5. We propose some means of reducing bone fracture, namely through improved housing designs and genetic selection.

Performance and welfare of laying hens in conventional and enriched cages

Concerns regarding the welfare of laying hens raised in battery cages have led to the development of enriched cages that allow hens to perform natural behaviors including nesting, roosting, and scratching. This study was conducted to compare indices of production and welfare in birds housed in 2 different caging systems. Shaver White hens were housed from 21 to 61 wk in either conventional battery cages (n = 500; 10 cages; 5 hens/cage; floor space = 561.9 cm(2)/hen) or enriched cages (n = 480; 2 cages; 24 hens/cage; floor space = 642.6 cm(2)/hen) and were replicated 10 times. Enriched cages provided hens with a curtained nesting area, scratch pad, and perches. Production parameters and egg quality measures were recorded throughout the experiment. Plumage condition was evaluated at 37 and 61 wk. Bone quality traits and immunological response parameters were measured at 61 wk, and 59 and 61 wk, respectively. Hen-day egg production, feed consumption, egg weight, and percentage of cumulative mortality of laying hens were not affected by the cage designs. Specific gravity and the percentage of cracked and soft-shelled eggs were also similar between the 2 housing systems. The incidence of dirty eggs was, however, significantly higher (P < 0.0001) in enriched cages than in conventional cages. Feather scores were similar between birds except for the wing region, which was higher (P < 0.05) for hens housed in conventional cages. Bone quality measures tended to be higher for hens housed in enriched cages compared with hens in conventional cages. However, the increase was significant only for bone mineral density. Immunological response parameters did not reveal statistically significant differences. Overall, laying performance, exterior egg quality measures, plumage condition, and immunological response parameters appear to be similar for hens housed in the 2 cage systems tested. Enrichment of laying hen cages resulted in better bone quality, which could have resulted from increased activity.

The influence of severe prolonged exercise restriction on the mechanical and structural properties of bone in an avian model

Many studies have described the effects of exercise restriction on the mammalian skeleton. In particular, human and animal models have shown that reduction in weight bearing leads to generalised bone loss and deterioration of its mechanical properties. The aim of this study was to assess the effect of prolonged exercise restriction coupled with heavy calcium demands on the micro-structural, compositional and mechanical properties of the avian skeleton. The tibiae and humeri of 2-year-old laying hens housed in conventional caging (CC) and free-range (FR) housing systems were compared by mechanical testing and micro-computed tomography (microCT) scanning. Analyses of cortical, cancellous and medullary bone were performed. Mechanical testing revealed that the tibiae and humeri of birds from the FR group had superior mechanical properties relative to those of the CC group, and microCT scanning indicated larger cortical and lower medullary regions in FR group bones. Cancellous bone analysis revealed higher trabecular thickness and a higher bone volume fraction in the FR group, but no difference in mineral density. The biomechanical superiority of bones from the FR group was primarily due to structural rather than compositional differences, and this was reflected in both the cortical and cancellous components of the bones. The study demonstrated that prolonged exercise restriction in laying hens resulted in major structural and mechanical effects on the bird skeleton.

Bone mineral density and breaking strength of White Leghorns housed in conventional, modified, and commercially available colony battery cages

Limited opportunity for movement and load-bearing exercise for conventionally caged laying hens leads to bone loss and increased susceptibility to osteoporosis, bone fractures, and cage layer fatigue, all of which compromise hen welfare and have negative consequences for production. The objective of this study was to compare bone mineral density (BMD) and strength measures of White Leghorns housed in conventional battery cages (CONV), cages modified to incorporate a nest box and perch (MOD), and commercially available, furnished colony cages with (CWDB) or without (CWODB) a raised dust bath. Hens reared on floor litter were randomly allocated to 1 of 4 cage systems at 19 wk of age. Hen-day production and egg quality were measured between 20 and 64 wk. At 65 wk, hens were killed, and right femur, tibia, and humerus were excised. Bone mineral density was assessed using quantitative computed tomography, and breaking strength was measured with an Instron Materials Tester. In the femur and tibia, CONV hens exhibited lower total BMD, bone mass, cortical bone area, cortical bone mass, and bone-breaking strength than CWDB, CWODB, and MOD hens. Density and cross-sectional area of bone in the trabecular space was highest in CONV. In the humerus, total and cortical BMD and mass and breaking strength values were higher for colony-housed birds than hens in CONV and MOD. The MOD birds did not exhibit increased humeral BMD or strength measures over CONV hens. These findings provide evidence that hens housed in modified and colony cages, furnished systems that promote load-bearing movement, are better able to preserve cortical structural bone than conventionally caged hens and simultaneously have stronger bones. Furthermore, inclusion of raised amenities that encourage wing loading is necessary to reduce humeral cortical bone loss. The overall absence of correlation between egg production or quality and bone quality measures also suggests that improved bone quality in CWDB, CWODB, and MOD furnished cages is not the result of lowered egg production or quality.

Relationships between genetic, environmental and nutritional factors influencing osteoporosis in laying hens

1. The effects upon bone quality of feeding limestone in flour or particulate form and housing type (cage or aviary) in lines of hens divergently selected for high (H) or low (L) bone strength over 7 generations were investigated. 2. As in previous generations, highly significant phenotypic differences between lines were observed in all measured bone traits at peak egg production (25 weeks) and towards the end of production (56 weeks) in both cage and aviary systems. 3. At 25 weeks there were no significant effects on bone variables of feeding particulate limestone although a significant reduction in osteoclast number was observed at this age. By 56 weeks osteoclast numbers were further reduced in hens fed particulate limestone and beneficial effects on some bone variables were observed in this treatment group. 4. The genotypic and dietary improvements upon bone quality were independent and additive at both ages. There were very few interactive effects. 5. Hens with the freedom to move in an aviary environment during the laying period had improved bone status compared to caged siblings. Environmental and genotypic effects were additive. 6. There were no effects of line on egg production although H line hens had slightly higher egg production by 56 weeks. Egg numbers were unaffected by diet. Eggshell thickness and strength were unaffected by line but hens fed particulate limestone had thicker- and stronger-shelled eggs over the production period as a whole. 7. We conclude that; (a) genetic selection is extremely effective in improving bone strength and resistance to osteoporosis; (b) allowing hens freedom to exercise can also improve bone strength but may increase the risk of keel damage if they do not have genetically-improved bone status; (c) feeding hens a particulate form of limestone from 15 weeks onwards can also increase bone strength and eggshell quality; (d) genetics, environment and nutrition all have independent and additive effects on bone status in laying hens but the relative effectiveness of these factors is genetics > environment > nutrition.

Use of apparent transverse quantitative ultrasonography to assess skeletal integrity in layers

Although there are several techniques currently available to assess skeletal integrity in live birds, few offer important features for application in a commercial setting, offering ease of use and moderate cost. Quantitative ultrasonography (QUS) is an established technique for diagnosis of osteoporosis in humans and horses that has potential application for layers. An OmniSense 700S quantitative ultrasonometer was evaluated for use with Single Comb White Leghorn hens. Humeral QUS values (m/s) were measured in a series of experiments using a total of 144 Shaver White hens. Significant correlations (P < 0.01) were observed among sequential QUS measurements taken on the same bird at 54, 60, and 66 wk of age. At the completion of the studies (66 wk of age), the left and right humeri were excised, cleaned, and rescanned. Postmortem QUS data from left and right humeri were related (R2 = 0.72, P < 0.0001), although future studies may need to consider both sides of the skeleton to account for asymmetry conditions. Ultrasound data collected from live hens at 66 wk of age correlated well with postmortem QUS data (R2 = 0.80, P < 0.0001). Quantitative ultrasonography did not correlate with humeral bone-breaking force measured postmortem. Bones from live hens, surrounded by tissue thicker than 4 mm, could not be read by the QUS probe.

Production, egg quality, bone strength, claw length, and keel bone deformities of laying hens housed in furnished cages with different group sizes

The effects of 3 different furnished cage systems (Aviplus, Eurovent 625a, Eurovent 625A) on 2 different laying hen strains [Lohmann Selected Leghorn (LSL), Lohmann Brown (LB)] were examined for the traits of production, egg quality, bone strength, claw length, and keel bone status. Two trials were carried out in which all hens received identical feeding and management. In brown hens, the traits egg production per average hen housed, cracked eggs, feed conversion, egg weight, and humerus breaking strength were significantly higher than in white hens. Furthermore, the claws of the brown hens were shorter than those of white hens. There were more dirty eggs, higher shell density, and fewer keel bone deformities in white hens than in brown hens. In the Aviplus system, egg production per average hen housed was higher than in the other systems, whereas shell thickness and density were lower. Humerus strength was also higher in the Aviplus than in the Eurovent 625a system, whereas there was no significant difference in tibia strength among the 3 systems. The shortest claws were found in the Aviplus system, and the fewest keel bone deformities occurred in the Eurovent 625a system. The study showed that the high standards of conventional cages for production and egg quality were met in furnished cages and that bone strength was significantly greater than in conventional cages. Claw shortening devices in furnished cages seemed satisfactory, because claws were generally short. However, the occurrence of keel bone deformities due to the intensive use of perches seemed to be a problem of furnished cages.

Assessing bone mineral density in vivo: digitized fluoroscopy and ultrasound

The genetic component of osteoporosis in caged laying hens is large, and a method for detecting hens susceptible to fracture could be useful in breeding programs. A radiographic absorptiometry film method was modified by video digitization from an image intensifier and computer analysis and termed digitized fluoroscopy (DF). Humeral and ulnar DF values were measured in 165 hens during lay. Relationships (P < 0.001) were seen between DF assessments from 25 wk onward and postmortem measurements at 70 wk. We conclude that DF can detect poor bones in hens early but is problematic. Quantitative ultrasound was also investigated. We measured amplitude-dependent speed-of-sound (Ad-SoS) in the third toe in hens. Nutritional studies revealed Ad-SoS values correlated with postmortem peripheral quantitative computerized tomography, (control group, r = 0.48, P < 0.001; treatment group, r = 0.39, P < 0.001). In caged and free-range hens, Ad-SoS correlated with shear strength (r = 0.33, P < 0.001, all hens) and radiographic density values (r = 0.53, P < 0.001, all hens) measured postmortem. The Ad-SoS values were higher in free-range than in caged hens (1,904 vs. 1,850 m/s, P < 0.001). Ad-SoS measurements were made in hens from a study where divergent genetic selection has produced high and low bone index lines with 92% difference in tibia strength. The value in high bone index hens was higher than in low bone index hens at 32 (P < 0.001), 42 (P < 0.001), 52 (P < 0.05), and 62 wk (P < 0.001) in generation 8. In an Ad-SoS heritability study, heritability estimates ranged from 0.15 to 0.39. We conclude that Ad-SoS is a heritable trait, reflects other bone measurements, and rapidly detects poor bone quality in hens.

Welfare implications of avian osteoporosis

Cage layer fatigue was first noticed after laying hens began to be housed in cages in the mid-20th century. Hens producing eggs at a high rate were most susceptible to the disease. Early research revealed that cage layer fatigue was associated with osteoporosis and bone brittleness. Severe osteoporosis leads to spontaneous bone fractures commonly in the costochondral junctions of the ribs, the keel, and the thoracic vertebrae. Vertebral fracture may damage the spinal cord and cause paralysis. Osteoporosis appears to be inevitable in highly productive caged laying hens. The condition can be made worse by metabolic deficiency of calcium, phosphorus, or vitamin D. Hens in housing systems that promote physical activity tend to have less osteoporosis and rarely manifest cage layer fatigue. Genetic selection may produce laying hens that are less prone to bone weakness. The welfare implications of osteoporosis stem from pain, debility, and mortality associated with bone fracture. The chicken has well-developed neural and psychological systems specialized to respond to pain associated with trauma and inflammation. Although studies on the chicken have not focused on pain due to bone fracture, physiological and behavioral similarities to other species allow inference that a hen experiences both acute and chronic pain from bone fracture. There is little information on osteoporosis in commercial caged layer flocks, however, evidence suggests that it may be widespread and severe. If true, most caged laying hens suffer osteoporosis-related bone fracture during the first laying cycle. Osteoporosis also makes bone breakage a serious problem during catching and transport of hens prior to slaughter. Estimates of mortality due to osteoporosis in commercial caged layer flocks are few, but range up to a third of total mortality. Many of these deaths would be lingering and attended by emaciation and possibly pain. Osteoporosis-related bone breakage during processing has reduced the marketability of spent caged laying hens, contributing to the need to develop humane on-farm killing methods to support alternative means of spent hen disposition. Overall, the evidence indicates that cage layer osteoporosis is a serious animal welfare problem. A determined effort must be made to make the laying hen no longer susceptible to the harmful effects of excessive bone loss.

Overview of bone biology in the egg-laying hen

In young pullets, long bones elongate by endochondral growth. Growth plate chondrocytes proliferate, then hypertrophy, and are replaced by osteoblasts that form a network of trabecular bone. This bone is gradually resorbed by osteoclasts as the bone lengthens. Long bones widen, and flat bones are formed, by intramembranous ossification in which cortical bone formation by osteoblasts in the periosteal layer is accompanied by osteoclastic resorption at the inner endosteal surface. Growth of structural trabecular and cortical bone types continues up to the onset of sexual maturity in pullets. At this point, the large surge in estrogen changes the function of osteoblasts to forming medullary bone rather than structural bone. Medullary bone is a woven bone that acts as a labile source of calcium for eggshell formation. It lines structural bone and also occurs as spicules within the marrow cavity. It has little inherent strength but can contribute to fracture resistance. Osteoclasts resorb both medullary and structural bone so that during the period the hen remains in reproductive condition there is a progressive loss of structural bone throughout the skeleton, which is characteristic of osteoporosis. The increasing fragility of the bones makes them more susceptible to fractures. The dynamics of bone loss can be affected by a number of nutritional, environmental, and genetic factors. If the hen goes out of reproductive condition, estrogen levels fall, osteoblasts resume structural bone formation, and skeletal regeneration can take place.

Behavioral evaluation of the psychological welfare and environmental requirements of agricultural research animals: theory, measurement, ethics, and practical implications

The welfare of agricultural research animals relies not only on measures of good health but also on the presence of positive emotional states and the absence of aversive or unpleasant subjective states such as fear, frustration, or association with pain. Although subjective states are not inherently observable, their interaction with motivational states can be measured through assessment of motivated behavior, which indicates the priority animals place on obtaining or avoiding specific environmental stimuli and thus allows conclusions regarding the impact of housing, husbandry, and experimental procedures on animal welfare. Preference tests and consumer demand models demonstrate that animal choices are particularly valuable when integrated with other behavioral and physiological measurements. Although descriptive assessments of apparently abnormal behavior such as stereotypies and "vacuum behaviors" provide indications of potentially impoverished environments, they should be used with some caution in drawing welfare conclusions. The development of stereotypies may in some cases be linked to psychiatric dysfunction and reflect underlying neurophysiological impairments, which have implications for the ability to perform flexible behavior and thus the quality of research data provided by this kind of behavioral measurement (e.g., in pharmaceutical research). Environmental modifications, commonly termed "enrichment," can have diverse consequences for cognitive function, physiological responses, health, psychological welfare, and research data. Simple practical modifications of housing, husbandry, and experimental design are suggested to improve the psychological welfare of agricultural research animals in accordance with the principles of refining, reducing, and replacing (the "3Rs"), which underlie US Public Health Service Policy, and prevailing public ethics.

Osteoporosis in cage layers

Osteoporosis in laying hens is a condition that involves the progressive loss of structural bone during the laying period. This bone loss results in increased bone fragility and susceptibility to fracture, with fracture incidences of up to 30% over the laying period and depopulation not uncommon under commercial conditions. A major cause of osteoporosis is the switch in bone formation from structural to medullary bone at the onset of sexual maturity, but structural bone loss is accelerated by the relative inactivity of-caged birds. Allowing birds more exercise, as in aviary systems, results in better bone quality but may not decrease the overall fracture incidence. Good nutrition can help to minimize osteoporosis but is unable to prevent it. Best nutritional practice involves transferring birds to a higher calcium diet at lighting up rather than at first egg, providing a source of calcium in particulate form, and not withdrawing feed some days before depopulation. Breeding may be an effective way of combating ostoporosis. Some bone strength traits have been shown to be heritable, and divergent selection for resistance or susceptibility to osteoporosis has resulted in lines with markedly different bone characteristics. After three generations of selection, the lines differ by 19% for keel bone mineral density, 13% for humerus breaking strength, and 25% for tibia breaking strength and show a sixfold difference in fracture incidence under commercial breeding conditions. The difference in bone quality among the lines is maintained under different housing systems.

Rearing without early access to perches impairs the spatial skills of laying hens

The effect of rearing with and without perches on the spatial ability of domestic hens (Gallus gallus domesticus) was investigated. No access or late access to perches during rearing has been shown to increase the later prevalence of floor eggs and cloacal cannibalism in loose-housed laying hens. This may be explained by either the birds reared without perches have difficulty using perches due to low muscle strength, lack of motor skills, and inability to keep balance, or they have impaired spatial skills necessary for moving around in three-dimensional space. These alternative explanations are not mutually exclusive.Thirty, day-old chicks were randomly allocated into two equal groups and reared in litter pens, one with access to perches (P+) and one without (P-). At 8 weeks of age, all birds were given access to perches, and by 15 weeks, all birds were using perches for roosting at night. At 16 weeks, 10 birds from each group were tested in pens where food was presented on a wire mesh tier 40 cm above the ground (T40). Three consecutive tests, with increasing difficulty for the bird to reach the food, were then performed. Firstly, the food was presented at 80 cm above the ground but with the tier at 40 cm still present; secondly, food was presented on the tier at 80 cm; and then, finally, with the food on a 160 cm high tier with the tier at 80 cm still present. All birds were food deprived for 15 h before each test and the time from the bird entering the pen until reaching the food was recorded. There was no difference in the time to reach the food between P+ and P- birds in the T40 test. But as the difficulty of the task increased, the difference between the P+ and P- birds became significant, with the P- birds taking a longer time to reach the food or not reaching it at all. Since there was no difference between P+ and P- in the T40 test, it seems reasonable to suppose that the later differences did not depend on differences in physical ability. Therefore, the results may imply that rearing without early access to perches, in some ways, impairs the spatial cognitive skills of the domestic hen.