Biomechanics of landing in injured and uninjured chickens and the role of meloxicam

Birds use their legs and wings when transitioning from aerial to ground locomotion during landing. To improve our understanding of the effects of footpad dermatitis (FPD) and keel bone fracture (KBF) upon landing biomechanics in laying hens, we measured ground-reaction forces generated by hens (n = 37) as they landed on force plates (Bertec Corporation, Columbus, OH) from a 30 cm drop or 170 cm jump in a single-blinded placebo-controlled trial using a cross-over design where birds received an anti-inflammatory (meloxicam, 5 mg/kg body mass) or placebo treatment beforehand. We used generalized linear mixed models to test for effects of health status, treatment and their interaction on landing velocity (m/s), maximum resultant force (N), and impulse (force integrated with respect to time [N s]). Birds with FPD and KBF tended to show divergent alterations to their landing biomechanics when landing from a 30 cm drop, with a higher landing velocity and maximum force in KBF compared to FPD birds, potentially indicative of efforts to either reduce the use of their wings or impacts on inflamed footpads. In contrast, at 170 cm jumps fewer differences between birds of different health statuses were observed likely due to laying hens being poor flyers already at their maximum power output. Our results indicate that orthopedic injuries, apart from being welfare issues on their own, may have subtle influences on bird mobility through altered landing biomechanics that should be considered.

Fear, anxiety, and production in laying hens with healed keel bone fractures

For laying hens, the immediate aftermath and healing period of a keel fracture (KF) is characterized by reduced ability to perform species-specific behavior, access resources, and pain. However, the longer-term impacts, once the fracture is completely healed, are less clear. As well as acute pain and behavioral changes, a negative experience can shape future responses to putatively threatening stimuli, raising future fear, and anxiety levels during husbandry-related events. We aimed to determine whether hens that had previously sustained keel bone fractures, but were now outside of the peak age range for new fractures, showed higher fear and anxiety levels compared to intact hens. We also determined if healed keel bone fractures were associated with reduced production, changes in behavior and resource use. One hundred and fifty hens with a palpation score of 1 ( "KF") and 150 hens with a palpation score of 0 (keel fracture free, "KFF") were selected from a commercial farm at 63 wk of age and housed in 6 groups (3 × KF and 3 × KFF). We compared production (hen weight and feed consumption, egg quantity, quality and weight, floor eggs, shell thickness, and weight) and home pen behavior (behaviors and transitional movements) in both groups. Finally, we measured the responses of KF (n = 75) and KFF (n = 75) during tonic immobility, novel arena, and novel object tests. KF and KFF hens did not differ in their responses to the tonic immobility, novel arena, and novel object tests, nor were there differences between the 2 groups in home pen behavior and transitional movements. KFF birds were lighter and laid eggs with less eggshell membrane compared KF birds, but no differences were found between KF and KFF in any other production measures. We found no evidence that healed KFs were associated with detrimental welfare effects in laying hens, but further work is required to determine the mechanisms and implications of the lower body weight and egg shell membrane.

Serum bone remodeling parameters and transcriptome profiling reveal abnormal bone metabolism associated with keel bone fractures in laying hens

Keel bone fractures affect welfare, health, and production performance in laying hens. A total of one hundred and twenty 35-wk-old Hy-line Brown laying hens with normal keel (NK) bone were housed in furnished cages and studied for ten weeks to investigate the underlying mechanism of keel bone fractures. At 45 wk of age, the keel bone state of birds was assessed by palpation and X-ray, and laying hens were recognized as NK and fractured keel (FK) birds according to the presence or absence of fractures in keel bone. The serum samples of 10 NK and 10 FK birds were collected to determine bone metabolism-related indexes and slaughtered to collect keel bones for RNA-sequencing (RNA-seq), Micro-CT, and histopathological staining analyses. The results showed that the concentrations of Ca, phosphorus, calcitonin, 25-hydroxyvitamin D₃, and osteocalcin and activities of alkaline phosphatase and tartrate-resistant acid phosphatase (TRAP) in serum samples of FK birds were lower than those of NK birds (P < 0.05), but the concentrations of parathyroid hormone, osteoprotegerin, and corticosterone in serum samples of FK birds were higher than those of NK birds (P < 0.05). TRAP staining displayed that FK bone increased the number of osteoclasts (P < 0.05). Micro-CT analysis indicated that FK bone decreased bone mineral density (P < 0.05). Transcriptome sequencing analysis of NK and FK bones identified 214 differentially expressed genes (DEGs) (|log2FoldChange| > 1, P < 0.05), among which 88 were upregulated and 126 downregulated. Kyoto Encyclopedia of Genes and Genomes pathway (KEGG) analysis indicated that 14 DEGs related to skeletal muscle movement and bone Ca transport (COL6A1, COL6A2, COL6A3, PDGFA, MYLK2, EGF, CAV3, ADRA1D, BDKRB1, CACNA1S, TNN, TNNC1, TNNC2, and RYR3) were enriched in focal adhesion and Ca signaling pathway, regulating bone quality. This study suggests that abnormal bone metabolism related to keel bone fractures is possibly responded to fracture healing in laying hens.

Keel bone damage affects behavioral and physiological responses related to stress and fear in two strains of laying hens

Keel bone damage (KBD) is more prevalent in alternative laying hen housing systems than in conventional cages, and its incidence differs from strain to strain. However, the information of KBD in Lindian chickens, a native Chinese strain, is limited. To investigate the effect of KBD on fearfulness and physiological indicators of stress in Lindian chickens and commercial laying hens, a total of two hundred 25-wk-old chickens (100 Hy-line Brown and 100 Lindian chickens) were studied for 7 wk. The birds were housed in furnished cages with 10 birds per cage for each strain. At 32-wk of age, the birds in each strain were divided into normal (NK), deviated (DK), and fractured (FK) hens according to the keel bone status. Ten birds in each keel bone status per strain were subsequently selected to collect blood for the determination of stress and fear-related indicators, including corticosterone, serotonin, interleukin-1β, and interleukin-6, and measure fear responses, including novel object test (NOT), human approach test (HAT), and tonic immobility (TI) test. The results showed that egg production was lower and the incidence of keel bone fractures was higher in Lindian chickens than in Hy-line Brown hens (P < 0.05). Lindian chickens showed a significantly increased whole blood serotonin content, NOT-latency, HAT-score, and TI induction times (P < 0.05) and decreased serum interleukin-6 content and TI-duration (P < 0.05) compared with Hy-line Brown hens. Additionally, FK hens had significantly elevated whole blood corticosterone, serum interleukin-1β and interleukin-6 levels, TI-duration, and NOT-latency (P < 0.05), and a reduced whole blood serotonin content (P < 0.05) compared with NK and DK hens. Our results indicated that KBD affected stress and fear responses, and this impact was mainly reflected by FK hens compared with NK and DK hens. We suggest that keel bone fractures are the main factor impairing hen welfare. Besides, the incidence of keel bone fractures and stress and fear responses of Lindian chickens are more severe than Hy-line Brown laying hens, indicating that the strain type can affect the health and welfare of laying hens.

A Descriptive Study of Keel Bone Fractures in Hens and Roosters from Four Non-Commercial Laying Breeds Housed in Furnished Cages

The presence of keel bone fractures (KBF) in laying hens has been documented and discussed by several authors, nevertheless the causative factors behind KBF remain uncertain. High prevalence of KBF have been reported in all commercial egg production systems, in different genetic lines and at different ages. Several of the proposed causal mechanisms behind KBF are linked to selection for efficient production. It is, therefore, of interest to explore whether less selected breeds have a lower occurrence of keel bone fractures compared to reports from highly selected, modern laying hen breeds. Thus, the aim of the current study was to investigate keel bones of hens from four non-commercial layer breeds. Birds were housed in furnished cages and keel bones examined at 30 and 63 weeks of age, using a portable X-ray equipment. The results from this descriptive study indicate a low prevalence of KBF at both ages in all four breeds, with only five KBF detected in 213 X-ray pictures taken from 126 birds. Of these, four of the KBF were observed in the most genetically selected breed, with an early onset of lay. None of the roosters examined exhibited KBF. The overall low numbers of KBF found indicate that genetic factors may be involved in KBF and, thus that selective breeding may help to reduce the susceptibility to KBF. Finally, this study highlights the importance of poultry conservation to secure genetic diversity, which may be an important resource in future selection schemes.

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

Keel bone damage (KBD) is a highly prevalent problem in commercial egg production. KBD consists of two different conditions affecting the keel: Keel bone deviation and keel bone fractures (KBF). Deviations are linked to pressure on the keel, e.g., from perching. The causative factors for KBF are not clear; however, selection for efficient egg production has been suggested as a major contributing factor. An important step to shed light on the role of selective breeding as an underlying cause of KBF in modern laying hens is to evaluate the keel bones of the ancestor, the red jungle fowl. To the authors' knowledge, this has never previously been published. The aim of this study was therefore to describe the prevalence of KBD in a study group of red jungle hens and roosters housed in an aviary system. The present study examined 29 red jungle fowls 112 weeks of age post-mortem; 12 hens and 17 roosters. Keel bones were evaluated by external palpation for deviations and fractures. Palpation was followed by autopsy. No fractures were detected in the 17 roosters; one had a very slight deviation. Of the 12 red jungle hens in this pilot study, one had a single fracture and 10 hens had a very slight deviation.

Keel bone fractures affect egg laying performance but not egg quality in laying hens housed in a commercial aviary system

The aim of this study was to investigate the effect of keel bone fracture (KBF) severity and healing activity on individual productivity of laying hens. Focal hens (75 Lohmann Selected Leghorn (LSL), 75 Lohmann Brown (LB)) were housed alongside non-focal hens in 10 identical pens containing a commercial aviary system (15 focal hens per pen). Eggs of focal hens were identified by orally administering a dye on 3 consecutive days, resulting in a hen-specific color pattern in the yolk. Eggs were collected at 7 time points (37 to 61 weeks of age; WOA) for 5 d to determine individual laying performance and to assess egg quality. Radiographs were performed to score KBF severity on a continuous scale. Healing activity was scored as inactive, healing, or fresh. Linear mixed effects models were used for statistical analyses. We found an association between KBF severity and reduced egg laying performance with increasing age (P = 0.005). At 37 WOA, egg laying performance was similar across KBF severities, whereas at 61 WOA, performance in hens with the highest observed KBF severity was 16.2% lower than in hens without fractures. Hens with fresh fractures had a lower performance than hens with healing and inactive fractures at 37 WOA but higher performance at 61 WOA (P = 0.02). Egg quality parameters were not affected by fractures but were associated with an age × hybrid interaction (egg mass: P = 0.039, shell breaking strength: P = 0.03, shell width: P = 0.001). In conclusion, hens could maintain high performance irrespective of fracture severity until shortly after peak of lay, but seemed to redirect available resources towards fracture healing if a fresh fracture was present. At the end of lay, the negative effect of KBF fracture severity on individual production amplified indicating that hens were no longer able to cope with the physiological challenge of a fracture.

Behavioral Differences of Laying Hens with Fractured Keel Bones within Furnished Cages

High prevalence of keel bone fractures in laying hens is reported in all housing systems. Keel fractures have been associated with pain and restricted mobility in hens in loose housing. The objective was to determine whether keel fractures were associated with activity of hens in furnished cages. Thirty-six pairs of LSL-Lite hens (72 weeks) were enrolled in the study. One hen with a fractured keel and one hen without were identified by palpation in each of 36 groups of hens housed in either 30- or 60-bird cages stocked at 750 cm²/hen. Behavioral activity of each hen was recorded by four observers blind to keel status using focal animal sampling for 10 min within a 2-h period in the morning (08:00–10:00), afternoon (12:00–14:00), and evening (17:00–19:00). All hens were observed during each of the three sample periods for 3 days totaling 90 min, and individual hen data were summed for analysis. Hens were euthanized 48 h after final observations, dissected, and classified by keel status: F₀ (no fracture, N = 24), F₁ (single fracture, N = 17), and F₂ (multiple fractures, N = 31). The percentages of time hens performed each behavior were analyzed using a mixed procedure in SAS with fracture severity, body weight, cage size, rearing environment, and tier in the model. Fracture severity affected the duration of perching (P = 0.04) and standing (P = 0.001), bout length of standing (P < 0.0001), and location (floor vs. perch) of resting behaviors (P = 0.01). F₂ hens perched longer than F₀ hens, 20.0 ± 2.9 and 11.6 ± 3.2%. F₂ hens spent less time standing, 15.2 ± 1.5%, than F₀ and F₁ hens, 20.7 ± 1.6 and 21.6 ± 1.8%. F₂ hens had shorter standing bouts (22.0 ± 4.2 s) than both F₀ and F₁ hens, 33.1 ± 4.3 and 27.4 ± 4.4 s. Non-fractured hens spent 80.0 ± 6.9% of total resting time on the floor, whereas F₁ and F₂ hens spent 56.9 ± 12.4 and 51.5 ± 7.7% resting on the floor. Behavioral differences reported here provide insight into possible causes of keel damage, or alternatively, indicate a coping strategy used to offset pain or restricted mobility caused by keel fractures.

Early Onset of Laying and Bumblefoot Favor Keel Bone Fractures

Numerous 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.

On-farm comparison of keel fracture prevalence and other welfare indicators in conventional cage and floor-housed laying hens in Ontario, Canada

The objective of this study was to compare the flock-level prevalence of healed keel bone fractures and to benchmark other indicators of well-being in laying hens housed in conventional cages and single-tier floor housing systems at several points during the production period. Commercial farms in Ontario, Canada, that housed hens in cages (n=9) or floor barns (n=8) were included. Flocks were beak-trimmed brown hens of various strains. Each flock was visited at 20, 35, 50, and 65 wk of age. At each visit, 50 hens were weighed, palpated for healed keel fractures, and feather scored over 4 areas of the body. Data were collected from the farm records on cumulative mortality. Keel fracture prevalence was higher in floor-housed flocks compared to cage-housed flocks (48.3±0.04% vs. 24.8±0.03%; P<0.001). The majority of keel fractures occurred by 50 wk. Cumulative mortality tended to be higher in floor-housed flocks compared to cage-housed flocks (2.13±0.42% vs. 1.29±0.19%; P=0.078). Mean BW was lower (1,827±28.8 g vs. 1,888±26.8 g; P=0.02) yet more uniform (CV of BW 9.43±0.40% vs. 10.10±0.32%; P<0.001) in floor-housed flocks compared to cage-housed flocks. Feather condition was not affected by housing system type (P=0.618), although it declined with age (P<0.001). Individual hen factors assessed using Pearson partial correlations indicated that hens with fractures were heavier at 65 wk in both housing types (P<0.05) and that heavier hens housed on the floor had better feather scores (P<0.001) from 35 wk onward. Floor-housed hens with fractures had lower feather scores at 35 wk (P<0.05) but not at 50 or 65 wk. Housing hens in single-tier floor systems increased the flock-level prevalence of keel fractures and resulted in a lower, yet more uniform, BW compared to hens in conventional cages under commercial conditions in Ontario. Benchmarking welfare indicators from alternative housing systems for laying hens is important to ensure that progress is made in improving their well-being.