Deoxynivalenol and fumonisin predispose broilers to bacterial chondronecrosis with osteomyelitis lameness

Bacterial chondronecrosis with osteomyelitis (BCO) lameness is the most critical animal health and welfare issue facing the broiler industry worldwide. It is estimated that 1 to 2% of bird condemnation at marketing age is caused by BCO lameness, resulting in tens of millions of dollars in annual losses. Fast-growing broilers are prone to mechanical stress that triggers bacterial translocation across epithelial barriers into the bloodstream, followed by bacterial colonization in the growth plate of long bones, and eventually, bone necrosis and lameness. Mycotoxins (MTX) are secondary metabolites produced naturally by microfungi, of which deoxynivalenol (DON), fumonisin (FUM), and zearalenone are the most prevalent in corn and soybean-meal-based diets. The presence of these mycotoxins in feed has been proven to reduce the barrier strength of the intestinal tracts and trigger immunosuppressive effects. In this study, we investigated the effects of the DON and FUM-contaminated feeds on the incidence of BCO lameness in broilers reared in both wire- and litter-floors. 720 one-day-old broiler chicks were assigned to the 2 × 2 factorial design: 2 MTX diets containing DON and FUM on wire flooring (MTX-W) and litter flooring (MTX-L), and 2 diets without MTX contamination on control wire flooring (CW) and control litter flooring (CL). Throughout the trial, the cumulative incidence of lameness per treatment was assessed by necropsying the lame birds. Birds in the MTX-W group had a higher incidence of lameness compared to those in CW (73.3% vs. 62.0%) (P < 0.05), and birds in the MTX-L group had a higher incidence of lameness compared to birds in CL (54.0% vs. 34.0%) (P < 0.05). MTX elicited net increases in BCO to a greater degree on litter (+20%) than on wire flooring (+12%). The increased incidence of BCO lameness in the MTX-W coincided with increased intestinal permeability supporting a correlation between intestinal barrier integrity and BCO lameness. To conclude, DON and FUM are predisposing factors for increasing BCO. However, no significant interaction exists between the diet and floor types in inducing lameness in broilers.

Inducing experimental bacterial chondronecrosis with osteomyelitis lameness in broiler chickens using aerosol transmission model

Lameness disease attributed to bacterial chondronecrosis with osteomyelitis in broilers affects production, animal welfare, and food safety in the poultry industry. The disease is characterized by necrotic degeneration of the rapidly growing femora and tibiae due to bacterial translocation from the respiratory or gastrointestinal tracts into the blood circulation, eventually colonizing the growth plate of the long bones. To investigate the etiology, pathogenesis, and intervention measures for BCO, developing an experimental model that reliably induces BCO lameness is of the utmost importance. In the past, we have employed a wire-flooring model and a litter-flooring model administered with a bacterial challenge to investigate strategies for mitigating BCO. However, multiple issues on labor-intensive barn setup and cleanout efforts for the wire-flooring system and concern of direct pathogenic exposure to the broilers for the litter-flooring models rendered these research models less effective. Thus, we investigated a new approach to induce experimental BCO lameness using an aerosol transmission model employing a group of birds reared on wire-flooring pens as a BCO infection source, and the disease is further disseminated through the airborne transmission to other birds reared on litter flooring in the same housing environment. The effectiveness of the aerosol transmission model in inducing BCO lameness was concluded from 4 independent experiments. The cumulative lameness generated from the BCO source group on the wire floors versus negative control treatments on the litter floors from Experiments 1, 2, 3, and 4 were 84% vs. 69.33%, P = 0.09; 54.55% vs. 60%, P = 0.56; 78% vs. 73.50%, P = 0.64; 81% vs. 74.50%, P = 0.11. Overall, the cumulative lameness generated from the wire floors was successfully transmitted to the birds on litter floors without significant statistical differences (P > 0.05). The effectiveness of the aerosol transmission model for experimentally triggering BCO lameness provides a reliable system for evaluating practical intervention strategies for BCO lameness in broilers.

Microencapsulation Improved Fumaric Acid and Thymol Effects on Broiler Chickens Challenged With a Short-Term Fasting Period

The first objective of this study was to demonstrate the usefulness of the microencapsulation technique to protect fumaric acid and thymol, avoiding their early absorption and ensuring their slow release throughout the gastrointestinal tract (GIT). For this purpose, the release of a lipid matrix microencapsulated brilliant blue (BB) was assessed in vitro, using a simulated broiler intestinal fluid, and in vivo. In vitro results showed that more than 60% of BB color reached the lower intestine, including 26.6 and 29.7% in the jejunum and ileum, respectively. The second objective was to determine the effects of microencapsulated fumaric acid, thymol, and their mixture on the performance and gut health of broilers challenged with a short-term fasting period (FP). One-day-old male ROSS 308 chickens (n = 280) were randomly distributed into seven treatments, with 10 replicates of four birds each. Dietary treatments consisted of a basal diet as negative control (NC), which was then supplemented by either non-microencapsulated fumaric acid (0.9 g/kg), thymol (0.6 g/kg), or a mixture of them. The same additive doses were also administered in a microencapsulated form (1.5 and 3 g/kg for the fumaric acid and thymol, respectively). At day 21, chickens were subjected to a 16.5-h short-term FP to induce an increase in intestinal permeability. Growth performance was assessed weekly. At day 35, ileal tissue and cecal content were collected from one bird per replicate to analyze intestinal histomorphology and microbiota, respectively. No treatment effect was observed on growth performance from day 1 to 21 (p > 0.05). Microencapsulated fumaric acid, thymol, or their mixture improved the overall FCR (feed conversion ratio) and increased ileal villi height-to-crypt depth ratio (VH:CD) (p < 0.001) on day 35 of the experiment. The microencapsulated mixture of fumaric acid and thymol increased cecal abundance of Bacteroidetes, Bacillaceae, and Rikenellaceae, while decreasing that of Pseudomonadaceae. These results indicate that the microencapsulation technique used in the current study can be useful to protect fumaric acid and thymol, avoiding early absorption, ensure their slow release throughout the GIT, and improve their effects on fasted broiler chickens.

Centennial Review: Trace mineral research with an emphasis on manganeseDedicated to Dr. Roland M. Leach, Jr

A century of publications in the Poultry Science journal is celebrated with Centennial papers. It is relevant, therefore, to explore trace mineral (TM) research with an emphasis on manganese and selected aspects of skeletal development. Some of the initial observations on the topic appeared in the earliest volumes of our journal. Published studies in the late 1920's and 1930's confirmed the importance of the diet and unidentified organic (i.e., vitamins) and inorganic nutrients (i.e., TM) relative to skeletal development. The early nutrition research emphasized requirement studies, the search for unknown factors to alleviate recognized deficiencies, and lastly important nutrient interactions, especially in the gut. This review will discuss TM research with an emphasis on manganese (Mn). Some of the fundamental discoveries on the mechanisms underlying embryonic and post-hatch skeletal development led directly to research directed at the role of Mn in the synthesis of the epiphyseal matrix. The TM research agenda today is considerably different with respect to all trace nutrients and is largely driven by gut health, antibiotic free production, food safety and environmental outcomes. A significant proportion of the published research over the last 2 decades has focused on the form (i.e., organic, inorganic) of a given TM relative to a given physiologic or production response under the pretext that modern commercial genotypes and production realities have changed considerably since the last NRC publication (NRC, 1994). If one closely reviews the more recent scientific literature, however, it could be argued that the term "trace mineral requirement" is often a misnomer. Many of the TM levels recommended or in use today are not the result of quantifiable requirement studies but are often based on efficacy comparisons with the different organic and inorganic forms of commercially available TM.

Nutritional Intervention Strategies Using Dietary Antioxidants and Organic Trace Minerals to Reduce the Incidence of Wooden Breast and Other Carcass Quality Defects in Broiler Birds

Wooden breast (WB) is a degenerative myopathy seen in modern broiler birds resulting in quality downgrade of breast fillets. Affected filets show increased toughness both before as well as after cooking and have decreased water holding capacity and marinade pick up compared to normal fillets. Although the exact etiology is unknown, the circulatory insufficiency and increased oxidative stress in the breast muscles of modern broiler birds could be resulting in damage and degeneration of muscle fibers leading to myopathies. Three independent experiments were conducted to evaluate the effect of various dietary interventions on the incidence of WB when birds are exposed to oxidative stress associated with feeding oxidized fat and mild heat stress. Feed additives such as dietary antioxidant [Ethoxyquin (ETX)], mineral methionine hydroxy analog chelate (MMHAC) of Zn, Cu, and Mn, and organic selenium (Org Se) were tested at recommended levels. In experiment 1, ETX reduced (P < 0.05) the incidence of severe WB induced by oxidized fat diet. The magnitude of improvement in percentage of normal (no WB) filets and reduction in muscle lipid peroxidation was greater (P < 0.05) when ETX and MMHAC were fed together as shown by experiment 2. In birds exposed to mild heat stress (Experiment 3), feeding MMHAC by itself reduced (P < 0.05) tissue damage by reducing incidence of tibial head lesions, skin scratches, breast blisters, in addition to increasing the incidence of normal (no WB) fillets. When MMHAC was combined with ETX and Org Se, further improvement (P < 0.05) in normal (no WB) filets was observed. In summary, under different oxidative stress conditions, dietary intervention programs that contain ETX, MMHA-Zn, -Cu, and -Mn and Org Se can improve performance and increase carcass integrity, reducing problems, such as WB, either independently or with additive effect. This effect is most likely attained by simultaneously improving the exogenous and endogenous antioxidant status, reducing oxidative stress, and improving tissue healing process of the bird.

Chondronecrosis with osteomyelitis in broilers: further defining lameness-inducing models with wire or litter flooring to evaluate protection with organic trace minerals

The feed additive Availa-ZMC was investigated for the ability to reduce lameness in broilers using 2 alternative models for inducing lameness. The mixture of organic trace minerals was effective in reducing lameness by 20% in the wire flooring model and 25% in the litter flooring model with the bacterial challenge. Lameness in both models is overwhelmingly attributable to bacterial chondronecrosis with osteomyelitis. The reduction in lameness was associated, at least in part, with enhanced intestinal barrier integrity mediated by elevated expression of tight junction proteins and stimulation of bactericidal killing of adherent peripheral blood monocytes obtained from the birds treated with Availa-ZMC. Lameness is a major animal welfare concern in broiler production. The wire flooring model and litter flooring model with the bacterial challenge are effective models for evaluation of management strategies for mitigating infectious causes of lameness.

Chondronecrosis with osteomyelitis in broilers: further defining a bacterial challenge model using standard litter flooring and protection with probiotics

This report demonstrates that high levels of lameness can be induced by a limited bacterial challenge in drinking water for birds raised on litter flooring, comparable with lameness induced by the gold standard for inducing lameness, growth on suspended wire flooring. The bacterium used in the challenge was cultured from lesions in birds induced for bacterial chondronecrosis with osteomyelitis (BCO) in the wire-flooring model so the epidemiology appears similar. The litter-flooring model could better approximate broiler operations. Furthermore, the work demonstrates that 2 commercial probiotics (GalliProTect and GalliProMax) can reduce lameness in the bacterial challenge litter-flooring model. Lameness attributable to BCO is one of the most significant animal welfare issues for broiler production. The wire-flooring and litter-flooring models afford alternatives for understanding the etiology, and epidemiology of BCO, and development of management strategies to reduce lameness. Probiotics afford a promising management strategy. The results suggest that the probiotic protection may extend beyond just intestinal health and intestinal barrier function.

RNA-seq reveals downregulated osteochondral genes potentially related to tibia bacterial chondronecrosis with osteomyelitis in broilers

Background

Bacterial chondronecrosis with osteomyelitis (BCO) develops in the growth plate (GP) of the proximal femur and tibia and is initiated by damage to the less mineralized chondrocytes followed by colonization of opportunistic bacteria. This condition affects approximately 1% of all birds housed, being considered one of the major causes of lameness in fast growing broilers. Although several studies have been previously performed aiming to understand its pathogenesis, the molecular mechanisms involved with BCO remains to be elucidated. Therefore, this study aimed to generate a profile of global differential gene expression involved with BCO in the tibia of commercial broilers, through RNA sequencing analysis to identity genes and molecular pathways involved with BCO in chickens.

Results

Our data showed 192 differentially expressed (DE) genes: 63 upregulated and 129 downregulated in the GP of the tibia proximal epiphysis of BCO-affected broilers. Using all DE genes, six Biological Processes (BP) were associated with bone development (connective tissue development, cartilage development, skeletal system development, organ morphogenesis, system development and skeletal system morphogenesis). The analyses of the upregulated genes did not indicate any significant BP (FDR < 0.05). However, with the downregulated genes, the same BP were identified when using all DE genes in the analysis, with a total of 26 coding genes explaining BCO in the tibia: ACAN, ALDH1A2, CDH7, CHAD, CHADL, COL11A1, COMP, CSGALNACT1, CYR61, FRZB, GAL3ST1, HAPLN1, IHH, KIF26B, LECT1, LPPR1, PDE6B, RBP4A, SERINC5, SFRP1, SOX8, SOX9, TENM2, THBS1, UCHL1 and WFIKKN2. In addition, seven transcription factors were also associated to BCO: NFATC2, MAFB, HIF1A-ARNT, EWSR1-FLI1, NFIC, TCF3 and NF-KAPPAB.

Conclusions

Our data show that osteochondral downregulated genes are potential molecular causes of BCO in broilers, and the bacterial process seems to be, in fact, a secondary condition. Sixteen genes responsible for bone and cartilage formation were downregulated in BCO-affected broilers being strong candidate genes to trigger this disorder.

Whole-Genome Comparisons of Staphylococcus agnetis Isolates from Cattle and Chickens

Staphylococcus agnetis has been previously associated with subclinical or clinically mild cases of mastitis in dairy cattle and is one of several staphylococcal species that have been isolated from the bones and blood of lame broilers. We reported that S. agnetis could be obtained frequently from bacterial chondronecrosis with osteomyelitis (BCO) lesions of lame broilers (A. Al-Rubaye et al., PLoS One 10:e0143336, 2015 [https://doi.org/10.1371/journal.pone.0143336]). A particular isolate, S. agnetis 908, can induce lameness in over 50% of exposed chickens, exceeding normal BCO incidences in broiler operations. We reported the assembly and annotation of the genome of isolate 908. To better understand the relationship between dairy cattle and broiler isolates, we assembled 11 additional genomes for S. agnetis isolates, an additional chicken BCO strain, and ten isolates from cattle milk, mammary gland secretions, or udder skin from the collection at the University of Missouri. To trace phylogenetic relationships, we constructed phylogenetic trees based on multilocus sequence typing and genome-to-genome distance comparisons. Chicken isolate 908 clustered with two of the cattle isolates, along with three isolates from chickens in Denmark and an isolate of S. agnetis we isolated from a BCO lesion on a commercial broiler farm in Arkansas. We used a number of BLAST tools to compare the chicken isolates to those from cattle and identified 98 coding sequences distinguishing isolate 908 from the cattle isolates. None of the identified genes explain the differences in host or tissue tropism. These analyses are critical to understanding how staphylococci colonize and infect different hosts and potentially how they can transition to alternative niches (bone versus dermis).IMPORTANCE Staphylococcus agnetis has been recently recognized as associated with disease in dairy cattle and meat-type chickens. The infections appear to be limited in cattle and systemic in broilers. This report details the molecular relationships between cattle and chicken isolates in order to understand how this recently recognized species infects different hosts with different disease manifestations. The data show that the chicken and cattle isolates are very closely related, but the chicken isolates all cluster together, suggesting a single jump from cattle to chickens.

Incidence of Bacterial Chondronecrosis with Osteomyelitis (Femoral Head Necrosis) Induced by a Model of Skeletal Stress and its Correlation with Subclinical Necrotic Enteritis

Bacterial chondronecrosis with osteomyelitis (BCO) is a septic necrosis of the skeletal system of unknown origin and an important cause of lameness in broiler chickens. Epithelial inflammation has been proposed as an avenue for bacterial translocation leading to BCO. We evaluated the effect of subclinical necrotic enteritis (SNE), an intestinal inflammatory event, with the development of BCO. In each of two experiments, chickens were divided into three treatments: (1) SNE challenge, including both dietary (wheat- and fish-based diet) and intestinal pathogenic challenges (Eimeria maxima and Clostridium perfringens), (2) dietary challenge only, and (3) control diet (corn-and soy-based diet). Floor ramps were introduced as part of an established method for increasing the frequency of BCO. The efficacy of the SNE challenge was corroborated by necropsy evaluation of a representative sample of the population. At the end of each experiment, all birds were evaluated for BCO. A high incidence of BCO was found, even in birds with no external signs of lameness. However, the incidence of BCO was not correlated with the intestinal challenge. Conclusions: under the conditions used in these studies, a treatment that is associated with severe damage to the intestinal mucosa does not change the incidence of BCO in broiler chickens.

The utility of infrared thermography for evaluating lameness attributable to bacterial chondronecrosis with osteomyelitis

Bacterial chondronecrosis with osteomyelitis (BCO) is a leading cause of lameness in broilers. Infrared thermography (IRT) is a noninvasive technique for measuring infrared radiation from an object and can be used to evaluate clinical health. Two replicated studies compared the effect of light intensity on broilers grown on a wire flooring model that experimentally increased their susceptibility to and incidence of BCO lameness. Day-of-hatch male broiler chickens were placed into 6 pens on wood shavings litter, and at 1 wk one of 3 light intensity treatments (2, 5, or 10 lux) was allotted. At 4 wk half of the population from each pen was moved to a pen with wire flooring and the same light intensity. At 1, 4, 5, and 8 wk, an IRT image of the legs of 5 clinically healthy broilers from each pen was taken. The right and left proximal femora and tibiae of sound and lame broilers were scored for femoral head necrosis (FHN) and tibial head necrosis (THN) lesion severity. There were minimal effects of light intensity and flooring. In Study 1, but not Study 2, broilers on wire flooring weighed less on day 38 (P = 0.007) and days 57 to 58 (P = 0.003) compared to those on litter. The proportion of broilers that became lame on wire flooring was 52% in Study 1 and 14% in Study 2. The proportion of sound broilers from litter and wire flooring pens with subclinical signs of BCO in their right or left proximal growth plates was over 45% for FHN and 92% for THN, and lame broilers had more severe (P < 0.0001) FHN and THN compared to sound broilers. IRT surface temperatures of the hock joint, shank, and foot were consistently lower (P < 0.0001) in broilers that became lame when compared to sound. Therefore, IRT surface temperatures of broiler leg regions may be useful for detecting lesions attributed to BCO.

Omega-3 fatty acids and meloxicam supplementation and the incidence and histopathological changes associated with femoral head syndrome in broilers

Femoral head separation (FHS) is one of the problems commonly found in fast growing-type broilers that resulted in joint inflammation leading to lameness and poor animal welfare. This study aimed to examine the alimentary effects of omega-3 fatty acids (DHA) and meloxicam on the incidence of FHS in relation with changes in pathological features and serum concentrations of TNFα and IL1β in broilers. A total number of 1152 male day-old Cobb 500 broilers were divided into four groups. The chicks in T1 (Control) received the basal diet. Chicks in T2 to T4 were given burden of a modified speed bump, in which the chicks in T2 received the basal diet, and the chicks in T3 and T4 received 2% All-G-Rich (16% DHA) in the basal diet and meloxicam in drinking water (0.5 mg/kg BW) during Days 22–43 of age, respectively. It was demonstrated that the incidence of FHS in T4 was the smallest (P &lt; 0.05) among groups although the incidence of FHS was not increased by modified speed bump itself. Although BW (and average daily gain) in T3 was the smallest, but the incidence of FHS was not decreased. An osteochondrosis cleft during histopathological examination could be detected even in the normal gross lesions. Serum concentrations in TNFα and IL1β were not different among groups. In conclusion, meloxicam as an anti-inflammatory drug was useful to alleviate the gross pathological changes of FHS whereas DHA was not effective at the used dosage. Studies on histopathological changes at the beginning of FHS lesion are necessary.

Poultry Femoral Head Separation and Necrosis: A Review

Femoral head separation (FHS) is a degenerative skeletal problem in fast-growing poultry wherein the growth plate of the proximal femur separates from its articular cartilage. At its early phase, FHS may remain asymptomatic but lead to epiphyseal breakage, infection, and femoral head necrosis (FHN). Healthy femoral head is viewed as a positive trait for genetic selection. However, the etiology of FHS is poorly understood for use in noninvasive diagnosis and genetic selection. Focal cell death and atrophic changes are likely associated with separation of tissues and necrotic changes. Fibrotic thickening of the articular surface can also impair free movement of the proximal epiphysis in the acetabulum, leading to FHS, under strain. The major limitation to understanding the pathophysiology of FHN is the lack of suitable experimental models and biomarkers to diagnose the problem. In this review, we discuss the possible etiologic factors, anatomic features of the chicken femoral head, biomarkers, and molecular mechanisms relevant to FHN.

Genome Analysis of Staphylococcus agnetis, an Agent of Lameness in Broiler Chickens

Lameness in broiler chickens is a significant animal welfare and financial issue. Lameness can be enhanced by rearing young broilers on wire flooring. We have identified Staphylococcus agnetis as significantly involved in bacterial chondronecrosis with osteomyelitis (BCO) in proximal tibia and femorae, leading to lameness in broiler chickens in the wire floor system. Administration of S. agnetis in water induces lameness. Previously reported in some cases of cattle mastitis, this is the first report of this poorly described pathogen in chickens. We used long and short read next generation sequencing to assemble single finished contigs for the genome and a large plasmid from the chicken pathogen. Comparison of the S. agnetis genome to those of other pathogenic Staphylococci shows that S.agnetis contains a distinct repertoire of virulence determinants. Additionally, the S. agnetis genome has several regions that differ substantially from the genomes of other pathogenic Staphylococci. Comparison of our finished genome to a recent draft genome for a cattle mastitis isolate suggests that future investigations focus on the evolutionary epidemiology of this emerging pathogen of domestic animals.

Efficacy of 25-OH Vitamin D3 prophylactic administration for reducing lameness in broilers grown on wire flooring

Bacterial chondronecrosis with osteomyelitis (BCO) is the most common cause of lameness in commercial broilers. Growing broilers on wire flooring provides an excellent experimental model for reproducibly triggering significant levels of lameness attributable to BCO. In the present study we evaluated the efficacy of adding HyD (25-OH vitamin D3) to the drinking water as a preventative/prophylactic treatment for lameness. Broiler chicks were reared on 5 x 10 ft flat wire floor panels within 6 environmental chambers. Three chambers were supplied with tap water (Control group) and the remaining chambers were supplied with HyD (HyD group: 0.06 mL HyD solution/L water; dosing based on the HyD Solution label to provide 33.9 μg 25-OHD3/L) from d 1 through 56. Feed was provided ad libitum and was formulated to meet or exceed minimum standards for all ingredients, including 5,500 IU vitamin D3/kg. Lameness initially was detected on d 28, and the cumulative incidence of lameness on d 56 was higher in the Control group than in the HyD group (34.7 vs. 22.7%, respectively; P = 0.03; Z-test of proportions; chambers pooled). The most prevalent diagnoses for lame birds were osteochondrosis and osteomyelitis (BCO) of the proximal femora (52%) and tibiae (79%), accompanied by minor incidences of tibial dyschondroplasia (0.33%), spondylolisthesis, or kinky back (0.67%), and twisted legs (1%). Broilers that survived to d 56 without developing lameness did not differ in BW when compared by group within a gender. The wire flooring model imposes a rigorous, sustained challenge that undoubtedly is much more severe than typically would be experienced by broilers under normal commercial conditions. Therefore the encouraging response to HyD supplementation in the present study supports the potential for 25-OH vitamin D3 to attenuate outbreaks of lameness caused by BCO in commercial broiler flocks.

Duck gait: Relationship to hip angle, bone ash, bone density, and morphology

The rapid growth meat birds, including ducks, undergo requires skeletal integrity; however, fast growth may not be conducive to adequate bone structure. A relationship likely exists between skeletal changes and duck mobility. Reduced mobility in meat ducks may have impacts on welfare and production. This study examined the relationships among gait score, bone parameters, and hip angle. Commercial Pekin ducks, ages 14 d (n = 100), 21 d (n = 100), and 32 d (n = 100) were weighed and gait scored with a 3-point gait score system by an observer as they walked over a Tekscan gait analysis system. Gait was scored as GS0, GS1, or GS2 with a score of GS0 defined as good walking ability and a score of GS2 as poorest walking ability. Ducks were humanely euthanized, full body scanned using quantitative computed tomography (QCT), and the right femur and tibia were extracted. Leg bones were cleaned, measured, fat extracted, and ashed. QCT scans were rendered to create computerized 3D models where pelvic hip angles and bone density were measured. Statistical analysis was conducted using PROC MIXED with age and gait score in the model. Body weight increased with age, but within an age, body weight decreased as walking ability became worse (P < 0.01). As expected, linear increases in tibia and femur bone width and length were observed as the ducks aged (P < 0.01). Right and left hip angle increased with duck age (P < 0.01). Additionally, ducks with a GS2 had wider hip angles opposed to ducks with a GS0 (P < 0.01). Bone density increased linearly with both age and gait score (P < 0.05). Femur ash content was lowest in 32-day-old ducks and ducks with GS1 and GS2 (P < 0.0001). Tibia ash content increased with age, but decreased as gait score increased (P < 0.001). The observation that right hip angle changed with gait scores merits further investigation into the relationship between duck mobility and skeletal changes during growth.