Infectious components of broiler lameness: a review

Myotendinopathy of Unknown Etiology in Broiler Breeder Males

This case series describes an emerging and ongoing lameness condition observed in broiler breeder males in flocks owned by a broiler integrator in the United States between February 2021 and April 2023. The lameness is characterized by an upright, penguin-like posture and gait. Affected flocks are typically 12-22 wk of age at presentation, but birds with similar stance and gross lesions can be observed as early as 1 day of age. Male mortality associated with this condition ranges from 0.01% to 6% per flock. The condition is infrequently observed in pullets from the female line but has not been observed in males (sex slips) from the female line. On postmortem examination, affected birds have bilateral hemorrhage due to a tearing of the iliotibialis muscles and fascia. In one case, a higher proportion of affected birds had unilateral lesions concurrently with broken legs or severe inguinal vaccine reaction. In this case, the affected leg was the weight-bearing leg. Histopathology confirmed the presence of hemorrhage in fascial sheaths surrounding major muscles, in addition to muscle fiber necrosis, edema, fibroplasia, and dissociation of tendon collagen. Bacteriology, histopathology, and clinical presentation identified no factors that were suggestive of an infectious etiology for this condition. No etiology has been established, but a suggested pathogenesis involves excessive biomechanical force resulting in tendon structural stress, leading to separation of tendon collagen fibers and associated muscle fiber stretching, separation, necrosis, and hemorrhage. The condition has been reported in multiple genetic lines, but the role of inheritance in the condition has not been fully evaluated.

Assessment of Welfare Problems in Broilers: Focus on Musculoskeletal Problems Associated with Their Rapid Growth

The growth of the broiler industry has been accompanied with concerns over the environmental and social impacts on intensive production systems, as well as the welfare of the animals themselves. As a result, since the 2000s, there has been growing interest in alternative production systems that improve animal welfare and sustainability. In this context, it is important to prioritize the welfare of broilers in commercial production systems and to use reliable welfare indicators to provide consumers with information about the welfare of the animals they consume. Resource-based measures (RBM) are based on assessing the resources available to the birds in terms of their housing, environment, and management practices, such as stocking density, litter quality, lighting and air quality, etc. Outcome-based measures (OBM), also known as animal-based measures, focus on assessing the actual welfare outcomes for the birds, such as footpad dermatitis, hock burn, contamination or damage to feathers, gait score, mortality, etc. These OBM-based measures are one of the more direct indicators of welfare and can help identify any welfare issues. The present review highlighted the factors that affect animal welfare indicators focused on OBMs which can be used in the commercial broiler farms.

Effect of exogenous genistein on osteogenic differentiation of adipose-derived mesenchymal stem cells in laying hens

Previous literature revealed that genistein might play a preventive role in osteoporosis. Therefore, we aimed to evaluate the effect of genistein on the osteogenic potency of laying hens' adipose-derived stem cells (LHASCs). The viability of LHASCs after isolation was investigated on tissue culture plastic (TCP) under exposure to genistein up to 50 μg/mL by MTT assay. Our preliminary result revealed that LHASCs cultured under genistein exposure up to 20 μg/mL are feasible. Then, we evaluated the osteogenic induction of LHASCs under exposure to 0, 10, and 20 μg/mL genistein. The Alizarin Red staining confirmed the calcium deposition. Our findings showed that osteogenic differentiation under exposure to 20 μg/mL genistein led to higher ALP activity and more calcium content. We then tried to see the probable additive effect of the genistein-plus Poly-L-lactic acid (PLLA) scaffold on the cell viability and osteogenic capacity of LHASCs. For this, cells were cultured on a PLLA scaffold and exposed to 20 μg/mL genistein. Cell growth rate, as indicated by the MTT assay, revealed no differences between the groups. LHASCs cultured on a genistein-plus PLLA scaffold showed higher ALP activity and more calcium content. The expressions of Osteocalcin, COL1A2, ALP, and Runx2 genes were increased in the genistein-plus PLLA group as compared with PLLA and TCP groups. Adequate proliferation rates and higher expression of osteogenic markers provide genistein as a suitable substrate to support the proliferation and differentiation of LHASCs. Genistein supports osteogenic induction as a further positive effect if such a PLLA scaffold is available.

Individual Monitoring of Activity and Lameness in Conventional and Slower-Growing Breeds of Broiler Chickens Using Accelerometers

Accelerometers are increasingly being investigated to detect animal behavior as a method for monitoring individual welfare that overcomes manual challenges associated with time, resource, and discrete sampling. We investigated the effects of broiler chicken hybrid (hereafter breed) and weight on accelerometer activity (activityA; calculated as percentage of time spent active (%)) and its association with lameness as a major broiler welfare concern. Accelerometers were attached to birds of different breeds on between 2 and 4 occasions from 26 to 30 days old (conventional breed CNV) and 26 to 49 days old (two slower-growing breeds SGH; SGN). At 2.2 kg, lameness was scored using a 6-point gait scoring system (0: unaffected to 5: severely lame). Linear mixed effects models and breed-stratified generalized linear models together with a random-effect meta-analysis were used for data analyses. ActivityA was lower in faster-growing, heavier birds compared to slower-growing, lighter birds, showing overall consistency with previous behavioral research, but did not vary linearly with gait score. Accelerometers offer the potential for simple broad-scale continuous monitoring of broiler chicken activity behavior that requires limited data processing. Exploration of the ability of accelerometers to capture more subtle and specific changes in behavioral patterning, such as non-linear acceleration with gait score that could indicate early development of lameness, warrants further investigation.

Case Report of Puffinosis in a Manx Shearwater (Puffinus puffinus) Suggesting Environmental Aetiology

Puffinosis is a disease of a range of seabirds characterised by dorsal and ventral blistering of their webbed feet, conjunctivitis, dry necrosis, leg spasticity, head shaking, loss of balance, tremors, and death. It is associated with Manx shearwaters (Puffinus puffinus), frequently affecting chicks within their underground nesting burrows. The aetiology of the disease is unclear but has been attributed to a type-2 coronavirus associated with Neotombicula mites as a potential vector. However, there is some uncertainty given potential laboratory contamination with mouse hepatitis virus and failure to fulfil Koch's postulates, with birds injected with isolates remaining healthy. We describe a detailed case report of puffinosis in a Manx Shearwater covering necropsy, histology, bacteriology, and metagenomics including viral sequencing. We found no evidence of viral infection or parasites. Our results are consistent with an entirely environmental aetiology, with caustic faecal ammonia in damp nesting burrows causing conjunctivitis and foot dermatitis breaking the skin, allowing common soil bacteria (i.e., Flavobacterium, Staphylococcus and Serratia spp., Clostridia perfringens and Enterococcus faecalis) to cause opportunistic infection, debilitating the bird and leading to death. A similar condition (foot pad dermatitis or FPD) has been reported in broiler chickens, attributed to caustic faeces, high humidity, and poor environmental conditions during indoor rearing, preventable by adequate ventilation and husbandry. This is consistent with puffinosis being observed in Shearwater nesting burrows situated in tall, dense, vegetation (e.g., bracken Pteridium aquilinum) but rarely reported in burrows situated in well-ventilated, short coastal grasslands. This proposed environmental aetiology accounts for the disease's non-epizootic prevalence, spatial variation within colonies, and higher frequency in chicks that are restricted to nesting burrows.

Review on skeletal disorders caused by Staphylococcus spp. in poultry

Lameness or leg weakness is the main cause of poor poultry welfare and serious economic losses in meat-type poultry production worldwide. Disorders related to the legs are often associated with multifactorial aetiology which makes diagnosis and proper treatment difficult. Among the infectious agents, bacteria of genus Staphylococcus are one of the most common causes of bone infections in poultry and are some of the oldest bacterial infections described in poultry. Staphylococci readily infect bones and joints and are associated with bacterial chondronecrosis with osteomyelitis (BCO), spondylitis, arthritis, tendinitis, tenosynovitis, osteomyelitis, turkey osteomyelitis complex (TOC), bumblefoot, dyschondroplasia with osteomyelitis and amyloid arthropathy. Overall, 61 staphylococcal species have been described so far, and 56% of them (34/61) have been isolated from clinical cases in poultry. Although Staphylococcus aureus is the principal cause of poultry staphylococcosis, other Staphylococcus species, such as S. agnetis, S. cohnii, S. epidermidis, S. hyicus, S. simulans, have also been isolated from skeletal lesions. Antimicrobial treatment of staphylococcosis is usually ineffective due to the location and type of lesion, as well as the possible occurrence of multidrug-resistant strains. Increasing demand for antibiotic-free farming has contributed to the use of alternatives to antibiotics. Other prevention methods, such as better management strategies, early feed restriction or use of slow growing broilers should be implemented to avoid rapid growth rate, which is associated with locomotor problems. This review aims to summarise and address current knowledge on skeletal disorders associated with Staphylococcus spp. infection in poultry.

A Meta-Analysis on the Significance of Dietary Omega-3 Fatty Acids on Bone Development and Quality in Egg- and Meat-Type Chickens

Poultry egg and meat production continue to be optimized for productivity and efficiency. However, genetic selection focusing on production efficiency has overlooked other aspects critical to bird wellbeing, such as skeletal development. As a result, modern birds are more prone to leg weakness, osteoporosis, and, subsequently, fractures. Dietary omega-3 polyunsaturated fatty acid (n-3 PUFA) enrichment has been proposed to benefit bone development, quality, and strength. However, there is a lack of conclusive and quantitative results across studies. Therefore, a meta-analysis approach was used to evaluate published studies to determine the effects of dietary n-3 PUFA enrichment on bone quality in laying- and meat-type birds. Publications were retrieved from multiple sources (databases and hand searching), and ten studies were selected for inclusion in the final dataset. A model to predict tibial bone ash content (BAC) was developed in Proc MIXED of SAS, treating the study as a random effect. The dietary concentration of n-3 PUFA, n-3 PUFA:n-6 PUFA ratio, calcium (Ca), phosphorus and feeding duration (days) were used as independent variables to predict BAC. The final model included the dietary n-6:n-3 FA ratio and the calcium concentration in the diet. The final model was selected based on the corrected Akaike Information Criteria, the root mean square prediction error (0.999) and its components, and the concordance correlation coefficient (CCC) (0.99). In laying-type birds, BAC was reduced by n-3 PUFA (p = 0.001) but was increased by Ca (p = 0.014). In contrast, in broiler chickens, BAC was increased by n-3 PUFA (p = 0.001) and decreased by Ca (p = 0.014). The influence of n-3 PUFA:n-6 PUFA ratio on tibia BAC in laying-type birds was not statistically significant (p = 0.505), whereas in meat-type birds, the influence of PUFA ratio was significant (p < 0.05). These results may indicate a low biological significance in laying-type birds but not in meat-type birds.

Influence of Feeding Omega-3 Polyunsaturated Fatty Acids to Broiler Breeders on Indices of Immunocompetence, Gastrointestinal, and Skeletal Development in Broiler Chickens

Modern broiler chickens are associated with rapid growth rates and superior feed efficiency. However, they are also susceptible to physiological and metabolic disorders (e.g., skin lesions, lameness, sudden death, enteric diseases, myopathies) that exert substantial economic losses to producers. This is further exacerbated by consumer pressure and mandated cessation of production practices such as indiscriminate use of antimicrobial growth promoters. Manipulation of broiler breeder (BB) nutrition and management can influence chick quality, robustness, and resilience to stressors in the production environment. The present review examines the role of feeding BB functional polyunsaturated omega-3 fatty acids (n-3 PUFA) and subsequent impact on the indices of immunocompetence, skeletal, and gastrointestinal (GIT) development in broiler chickens. Research in mammalian and avian models led evidence that perinatal feeding of long chain n-3 PUFA such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) engender transgenerational effects through regulation of a variety of biological processes including development of vital organs such as skeleton, brain and GIT. It is shown that feeding poultry breeders n-3 PUFA decreases inflammatory states and enriches hatching eggs with n-3 PUFA and immunoglobulins. Further evidence also shows that after 15 days of incubation, chicken embryos preferentially utilize long chain n-3 PUFA-critical for optimal cell, tissues, and organ development. Enrichment of n-3 PUFA in newly hatchling tissues reduce proinflammatory eicosanoids with consequences of enhanced bone mineralization. Dietary n-3 PUFA also modulates breeder GIT microbiota with consequences of microbial colonization and succession in chicks. As well, research shows that feeding poultry breeders n-3 PUFA bolsters progeny immunocompetence through enhanced passive immunity and antibody titres against routine vaccination. In conclusion, it appears that chicks may benefit from the incorporation of n-3 PUFA in the breeder diets; however, little attention is paid to fatty acids composition in breeder nutrition. We also highlight gaps in knowledge and future research perspectives.

The relationship between gait and automated recordings of individual broiler activity levels

Gait, or walking ability, is an often-measured trait in broilers. Individual gait scores are generally determined manually, which can be time-consuming and subjective. Automated methods of scoring gait are available, but are often implemented at the group level. However, there is an interest in automated methods of scoring gait at the individual level. We hypothesized that locomotor activity could serve as a proxy for gait of individual broilers. Locomotor activity of 137 group-housed broilers from four crosses was recorded from approximately 16 to 32 days old, using an ultra-wideband tracking system. These birds were divided over four trials. Individual gait scores were determined at the end of the tracking period, on a scale from 0 to 5, with higher scores representing worse gait. Given the limited number of birds, birds were subsequently categorized as having a good gait (GG; scores 0–2) or a suboptimal gait (SG; scores 3–5). Relationships between activity and gait classification were studied to determine whether individual activity has the potential to serve as a proxy for gait. When comparing GG and SG birds using robust linear regression, SG birds showed a lower 1) activity around the start of tracking (estimate = −1.33 ± 0.56, P = 0.019), 2) activity near the end of tracking (estimate = −1.63 ± 0.38, P < 0.001), and 3) average activity (estimate = −1.12 ± 0.41, P = 0.007). When taking day of tracking, trial, cross and body weight category (heavy versus light at approximately 2 wk old) into account, a tendency was still observed for SG birds having lower activity levels within lightweight birds, but not within heavyweight birds. This study provides indications for activity differences between gait classifications. However, given that there was considerable overlap in activity levels between the gait classifications, future research implementing additional activity-related variables is required to allow a more complete distinction between birds with different gait classifications.

Analysis of genomes of bacterial isolates from lameness outbreaks in broilers

We investigated lameness outbreaks at 3 commercial broiler farms in Arkansas. We isolated several distinct bacterial species from Bacterial Chondronecrosis with Osteomyelitis (BCO) lesions from these 3 farms. The results show that BCO-lameness pathogens on particular farms can differ significantly. We characterized genomes for isolates of the 2 most prevalent species, Escherichia coli and Staphylococcus aureus. Genomes assembled for E. coli isolates from all 3 farms were quite different between farms, and most similar to genomes from different geographical locations and hosts. The E. coli phylogenomics suggests frequent host shifts for this species. Genomes for S. aureus isolates from one farm were highly related to those from chicken isolates from Europe. Highly related isolates have also been characterized from chickens in the Arkansas area for at least a decade. Phylogenomics suggest that this S. aureus has been restricted to poultry for more than 40 y. Detailed analysis of genomes from 2 neighboring clades of S. aureus human and chicken isolates, identifies the acquisition of a specific pathogenicity island in the transition from human to chicken pathogen and that pathogenesis for this clade in chickens may depend on this mobile element. Investigation of the evolution of this chicken-restricted clade from 1980 in Ireland, Poland in 2008, Oklahoma in 2010 and Arkansas in 2019, reveals the acquisition of additional virulence determinants including pathogenicity islands. Isolate-specific genome characterizations will help further our understanding of the disease mechanisms of BCO-lameness, a significant animal welfare issue.

Remedying Contact Dermatitis in Broiler Chickens with Novel Flooring Treatments

Simple Summary

Contact dermatitis is an overarching term for inflamed or necrotic lesions after contact with an allergen or irritant. Broiler chickens commonly experience these lesions due to prolonged contact with moisture, feces, and ammonia within litter. This study aimed to find methods to prevent and remedy lesions on broilers’ feet, hocks, and breast. Furthermore, the impact of treatments on plumage cleanliness, gait, and body weight was investigated. We applied novel flooring treatments consisting of plastic slats and disinfectant mats containing povidone-iodine, which we compared to the industry control (used litter) and a positive control (clean litter). Weekly measurements on a sample of birds in each pen showed us the impact of both flooring treatments and age (weeks) on animal welfare outcomes. Contrary to expectations, the novel flooring treatments did not prevent or remedy contact dermatitis. In fact, the positive control, consisting of replacing litter every four days, resulted in the best welfare condition, with limited to no contact dermatitis at week seven of age.

Abstract

Contact dermatitis (footpad dermatitis (FPD), hock burns, and breast dermatitis) is a welfare issue for broiler chickens, causing pain and behavioral restrictions. Once lesions develop, often nothing is done to remedy the issue for the affected flock. Our objective was to evaluate novel flooring treatments at the flock level by providing preventative and remedial treatments against contact dermatitis, plumage soiling, and gait impairment. Broilers (n = 546) were housed in 42 pens, with 13 birds/pen. The flooring treatments (four) included used litter (NEG), new pine shavings replaced regularly (POS), a mat filled with 1% povidone-iodine solution (MAT), and the iodine mat placed on a slatted floor (SLAT). Flooring treatments were provided from day one of age (preventative approach; PREV) or day 29 (remedial approach; REM). Contact dermatitis, soiling, gait, and weight were recorded weekly (seven birds/pen). Results showed a treatment effect for all measures, dependent on bird age. Overall, the POS treatment resulted in the best welfare outcomes (FPD, hock burns, and gait). The worst contact dermatitis was found in the MAT and SLAT groups. NEG birds showed little contact dermatitis, opposite to expectations. Weights were lower for PREV-POS in week seven only. The treatments with povidone-iodine were deemed ineffective against contact dermatitis. Access to clean litter prevented and remedied contact dermatitis, and a comparable approach may be commercially feasible.

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.

A Review of Current Knowledge on Staphylococcus agnetis in Poultry

Simple Summary

This literature review provides a synthesis and evaluation of the current knowledge on Staphylococcus agnetis (S. agnetis) and its implications in poultry pathology. Recent studies revealed that S. agnetis can cause bacterial chondronecrosis with osteomyelitis (BCO), endocarditis, and septicemia in broiler chickens. Lameness constitutes one of the major health and welfare problems causing huge economic losses in the poultry industry. To date, a range of infectious and non-infectious factors have been associated with lameness in poultry. Among bacteria of the genus Staphylococcus, Staphylococcus aureus is the main species associated with locomotor problems. This contrasts with S. agnetis, which until recently had not been considered as a poultry pathogen. Previously only reported in cattle, S. agnetis has expanded its host range to chickens, and due to its unique characteristics has become recognized as a new emerging pathogen. The genotypic and phenotypic similarities between S. agnetis and other two staphylococci (S. hyicus and S. chromogenes) make this pathogen capable of escaping recognition due to misidentification. Although a significant amount of research on S. agnetis has been conducted, many facts about this novel species are still unknown and further studies are required to understand its full significance in poultry pathology.

Abstract

This review aims to summarize recent discoveries and advancements regarding the characteristics of Staphylococcus agnetis (S. agnetis) and its role in poultry pathology. S. agnetis is an emerging pathogen that was primarily associated with mastitis in dairy cattle. After a presumed host jump from cattle to poultry, it was identified as a pathological agent in broiler chickens (Gallus gallus domesticus), causing lameness induced by bacterial chondronecrosis with osteomyelitis (BCO), septicemia, and valvular endocarditis. Economic and welfare losses caused by lameness are global problems in the poultry industry, and S. agnetis has been shown to have a potential to induce high incidences of lameness in broiler chickens. S. agnetis exhibits a distinct repertoire of virulence factors found in many different staphylococci. It is closely related to S. hyicus and S. chromogenes, hence infections caused by S. agnetis may be misdiagnosed or even undiagnosed. As there are very few reports on S. agnetis in poultry, many facts about its pathogenesis, epidemiology, routes of transmission, and the potential impacts on the poultry industry remain unknown.

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.

Associations between carcass weight uniformity and production measures on farm and at slaughter in commercial broiler flocks

In poultry flocks, flock weight uniformity is often defined as the percent individuals within 10% of the mean body weight (BW) and the variability of this uniformity can be expressed as the CV of BW. Flock weight uniformity is a standardized and objective measured, and could potentially be used as a welfare indicator; however, little is known about the relationship between flock uniformity and other production measures on-farm or at slaughter. The aim of this study was to investigate the associations between carcass weight uniformity (CV of BW) and production measures on-farm and at slaughter in Norwegian commercial broiler flocks. A total of 45 randomly selected mixed-sex Ross 308 broiler flocks were visited prior to slaughter at 28 to 30 D of age (average slaughter age 30.6 D). All flocks were raised under similar farm management systems. The Welfare Quality protocol for broilers was used to assess different animal welfare indicators in each flock. All production data from the slaughterhouse were collected for each flock, including carcass weight uniformity (%), mortality (%), growth rate (g), feed conversion ratio (FCR), and rejected birds (%) in different rejection categories. Univariable and multivariable linear regression models were used to investigate the associations between flock weight uniformity and production and welfare measures. The results showed that flock uniformity varied from 11% to 18% between flocks within the same hybrid, similar management standards, and similar slaughter age (day 29 to 32). Poorer uniformity (i.e., high CV) was associated with increased first week mortality (P < 0.004, r = 1.48, increased total mortality (P < 0.013, r = 0.01), increased FCR (i.e., less efficient growth) (P < 0.024, r = 0.06), reduced growth rate (P < 0.0012, r = −0.01), and a reduced rejection rate at slaughter (P < 0.006, r = −0.01). The results show that flock uniformity varies across broiler flocks, and is associated with several production measures.

Slaughter of animals: poultry

The killing of poultry for human consumption (slaughtering) can take place in a slaughterhouse or during on-farm slaughter. The processes of slaughtering that were assessed, from the arrival of birds in containers until their death, were grouped into three main phases: pre-stunning (including arrival, unloading of containers from the truck, lairage, handling/removing of birds from containers); stunning (including restraint); and bleeding (including bleeding following stunning and bleeding during slaughter without stunning). Stunning methods were grouped into three categories: electrical, controlled modified atmosphere and mechanical. In total, 35 hazards were identified and characterised, most of them related to stunning and bleeding. Staff were identified as the origin of 29 hazards, and 28 hazards were attributed to the lack of appropriate skill sets needed to perform tasks or to fatigue. Corrective and preventive measures were assessed: measures to correct hazards were identified for 11 hazards, with management shown to have a crucial role in prevention. Ten welfare consequences, the birds can be exposed to during slaughter, were identified: consciousness, heat stress, cold stress, prolonged thirst, prolonged hunger, restriction of movements, pain, fear, distress and respiratory distress. Welfare consequences and relevant animal-based measures were described. Outcome tables linking hazards, welfare consequences, animal-based measures, origins, and preventive and corrective measures were developed for each process. Mitigation measures to minimise welfare consequences were also proposed.

Lameness and its relationship with health and production measures in broiler chickens

The aim of this study was to explore lameness and the associations between lameness and health/production measures of animal welfare in commercial broiler production, using the Welfare Quality® protocol for broilers. A total of 50 flocks were included in the sample and farm visits were conducted for lameness scoring at a mean age of 28.9 days. The percentage of animals (n=7500) in the six different gait score (GS) categories were GS0: 2.53%, GS1: 44.19%, GS2: 33.84%, GS3: 16.32%, GS4: 2.36% and GS5: 0.53%. Production and other welfare data were collected for each flock after slaughter. Higher gait scores were associated with increased hock burn score (P<0.02), increased footpad dermatitis score (P<0.01), reduced bird cleanliness score (P<0.01) and peat litter (P<0.01). Although not statistically significant, there was a tendency for increased flock gait score being associated with wet litter (P=0.07). In addition, condemnations at postmortem inspection were associated with increasing gait scores (P<0.05), indicating that at least a portion of the lameness cases display pathological changes on the carcasses. In conclusion, 19%of the birds showed moderate-to-severe lameness, which was associated with several production or health and welfare observations including feather cleanliness and condemnations as unfit for human consumption at slaughter. Although stocking density and growth rate are already known key factors for lameness, associations of lameness with hock burns, footpad dermatitis and cleanliness of the birds suggest that a suboptimal physical environment (e.g. litter- and air quality) may be detrimental to leg health. Further studies are needed to explore these associations in more detail.

Salmonella Contamination in Broiler Synovial Fluid: Are We Missing a Potential Reservoir?

The objective of this study was to assess the presence and characteristics of Salmonella enterica found in the synovial fluid of broiler carcasses. The synovial fluid of three individual joints from 500 broiler carcasses was individually sampled from five broiler processing facilities located in the Southeast and West regions of the United States (1,500 total samples). The external surface of broiler carcass was decontaminated before sampling of the shoulder, coxofemoral, and tibiofemoral joints. Individual samples were enriched, composited, and subjected to rapid PCR-based detection of Salmonella. Individual samples from any positive composites were also enriched before determination of Salmonella presence in the same manner. Positive individual samples were subjected to secondary enrichment before plating onto selective agar for isolation of Salmonella. Salmonella isolates were serotyped before determination of antimicrobial susceptibility. Overall, 1.00% (5 of 500 broiler carcasses) of composite samples and 0.47% (7 of 1,500 samples) of individual samples were positive for Salmonella. Five of the seven isolates were susceptible to all drugs tested and determined to be Salmonella Enteritidis. The remaining two isolates, identified as Salmonella Typhimurium, were resistant to streptomycin. To our knowledge, no previous assessments of Salmonella in the synovial fluid of broilers has been reported; however, results of the present study suggested that the synovial fluid may be a reservoir for Salmonella in broilers. Although the prevalence of Salmonella is low, this information provides valuable insight into potential poultry contamination pathways and warrants further exploration.

Evaluating Pekin duck walking ability using a treadmill performance test

Gait scoring is the most popular method for assessing the walking ability of poultry species. Although inexpensive and easy to implement, gait scoring systems are often criticized for being subjective. Using a treadmill performance test we assessed whether observable differences in Pekin duck walking ability identified using a gait scoring system translated to differences in walking performance. One hundred and eighty ducks were selected using a three-category gait scoring system (GS0 = smooth gait, n = 55; GS0.5 = labored walk without easily identifiable impediment, n = 56; GS1 = obvious impediment, n = 59) and the amount of time each duck was able to sustain walking on a treadmill at a speed of 0.31 m/s was evaluated. The walking test ended when each duck met one of three elimination criteria: (1) The duck walked for a maximum time of ten minutes, (2) the duck required support from the observer's hand for more than three seconds in order to continue walking on the treadmill, or (3) the duck sat down on the treadmill and made no attempt to stand despite receiving assistance from the observer. Data were analyzed in SAS 9.4 using PROC GLM. Tukey's multiple comparison test was used to compare differences in time spent walking between gait scores. Significant differences were found between all gait scores (P < 0.05). Behavioral correlates of walking performance were investigated. Video recorded during the treadmill test was analyzed for counts of sitting, standing, and leaning behaviors. Data were analyzed in SAS 9.4 using a negative binomial model for count data. No differences were found between gait scores for counts of sitting, standing, and leaning behaviors (P > 0.05). In conclusion, the amount of time spent walking on the treadmill corresponded to gait score and was an effective measurement for quantifying Pekin duck walking ability. The test could be a valuable tool for assessing the development of walking issues or the effectiveness of treatments aimed at promoting leg health.

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.

Molecular survey of bacterial communities associated with bacterial chondronecrosis with osteomyelitis (BCO) in broilers

Bacterial chondronecrosis with osteomyelitis (BCO) is recognized as an important cause of lameness in commercial broiler chickens (meat-type chickens). Relatively little is known about the microbial communities associated with BCO. This study was conducted to increase our understanding of the microbial factors associated with BCO using a culture-independent approach. Using Illumina sequencing of the hyper-variable region V6 in the 16S rRNA gene, we characterized the bacterial communities in 97 femoral or tibial heads from normal and lame broilers carefully selected to represent diverse variations in age, line, lesion type, floor type, clinical status and bone type. Our in-depth survey based on 14 million assembled sequence reads revealed that complex bacterial communities exist in all samples, including macroscopically normal bones from clinically healthy birds. Overall, Proteobacteria (mean 90.9%) comprised the most common phylum, followed by Firmicutes (6.1%) and Actinobacteria (2.6%), accounting for more than 99% of all reads. Statistical analyses demonstrated that there are differences in bacterial communities in different types of bones (femur vs. tibia), lesion types (macroscopically normal femora or tibiae vs. those with pathognomonic BCO lesions), and among individual birds. This analysis also showed that BCO samples overrepresented genera Staphylococcus, whose species have been frequently isolated in BCO samples in previous studies. Rarefaction analysis demonstrated the general tendency that increased severities of BCO lesions were associated with reduced species diversity in both femoral and tibial samples when compared to macroscopically normal samples. These observations suggest that certain bacterial subgroups are preferentially selected in association with the development of BCO lesions. Understanding the microbial species associated with BCO will identify opportunities for understanding and modulating the pathogenesis of this form of lameness in broilers.

Evaluating portable wire-flooring models for inducing bacterial chondronecrosis with osteomyelitis in broilers

Rearing broilers on flat or sloping wire flooring is an effective method for consistently triggering lameness attributable to bacterial chondronecrosis with osteomyelitis (BCO). Portable obstacles known as speed bumps (SB) also consistently trigger modest incidences of BCO when they are installed between feed and water lines in litter flooring facilities. Two experiments were conducted to determine the most effective broiler age for introducing the SB into litter flooring pens, and to evaluate alternative configurations of the traditional SB with the expectation that amplified mechanical challenges to the legs of broilers should increase the incidence of BCO. Broiler chicks obtained from commercial hatcheries (lines B and D in experiment 1, lines A and B in experiment 2) were reared in floor pens with ad libitum feed and water and a 23L:1D photoperiod. In experiment 1, the 5 floor treatments included wood shavings litter only (L), flat wire only (W), or litter plus SB installed at 14, 28, or 42 d of age. Line B was more susceptible to lameness than line D (25.9 vs. 15.3% for all treatments combined; P = 0.001). Both lines developed low incidences of lameness on L (11 to 13%), intermediate incidences on SB regardless of day of installation (12 to 23%), and high incidences on W (21 to 39%). In experiment 2, broilers were reared with 7 floor treatments, including L, W, SB with a 50% slope (SB50%); SB50% with a limbo bar installed over the apex; SB with a 66% slope and limbo bar; SB50% with a nipple water line suspended over the apex; and a pagoda-top SB. All SB were inserted on d 28. Line B was more susceptible to lameness than line A (20.2 vs. 16.1% for all treatments combined; P < 0.05), and for both lines combined the lameness percentages averaged 7.7 (L), 29.2 (W), 17.3 (SB50%), 16.2 (SB50% with a limbo bar), 21.5 (SB with a 66% slope and limbo bar), 20.8 (SB50% with a nipple water line), and 11.5% (pagoda-top). These studies demonstrate the portable SB can be effectively used to experimentally trigger BCO in broilers.

Dexamethasone triggers lameness associated with necrosis of the proximal tibial head and proximal femoral head in broilers

Bacterial chondronecrosis with osteomyelitis (BCO) and turkey osteomyelitis complex (TOC) are characterized by bacterial infection and necrotic degeneration within the tibiae and femora. Stress and immunosuppression have been implicated in the pathogenesis of BCO and TOC. Immunosuppressive doses of dexamethasone (DEX) trigger high incidences of TOC in turkey poults. The present study was conducted to determine if DEX injections or heat stress can trigger BCO and lameness in broilers. In 3 independent experiments, broilers were weighed and either remained uninjected or received repeated injections of 0.9% saline or DEX dissolved in saline (0.45 to 1.5 mg of DEX/kg of BW). Across all 3 experiments, the incidences of lameness were 0% for uninjected controls, 0 to 8% in saline-injected groups, and 24 to 68% in groups injected with 0.9 to 1.5 mg of DEX/kg of BW. Growth was inhibited by DEX injections regardless of whether the birds became lame or survived. When compared with saline-injected groups, DEX injections consistently increased the incidence of severe proximal tibial head necrosis in lame birds as well as in survivors. The DEX injections also triggered a subset of lesions that are not considered pathognomonic for BCO (for example, avascular femoral head necrosis and fatty necrosis of the tibiae). In a fourth experiment, repeated episodes of heat stress did not trigger lameness, although the subclinical incidence of tibial head necrosis was substantially higher at 28 and 35 d of age in heat-stressed broilers when compared with broilers reared under thermoneutral conditions. Accordingly, stress and immunosuppression must be considered contributing factors in the pathogenesis of tibial and femoral lesions associated with lameness in broilers. A subset of the lesions triggered by repeated DEX injections did not precisely mimic the pathogenesis of BCO in broilers, and DEX consistently inhibited growth whereas BCO is associated with rapid growth. These caveats must be acknowledged when DEX is used to trigger lameness in broilers.

A wire-flooring model for inducing lameness in broilers: evaluation of probiotics as a prophylactic treatment

Bacterial chondronecrosis with osteomyelitis (BCO) is the most common cause of lameness in commercial broilers. Bacteria entering the blood via translocation from the respiratory system or gastrointestinal tract spread hematogenously to the proximal epiphyseal-physeal cartilage of rapidly growing femora and tibiae, causing BCO. We tested the hypothesis that rearing broilers on wire flooring should increase the incidence of BCO by persistently imposing additional torque and shear stress on susceptible leg joints. We also tested the hypothesis that probiotics might attenuate bacterial translocation and thereby reduce the incidence of BCO. In 5 independent experiments using 4 commercial lines, broilers grown on wire flooring developed lameness attributable predominately to BCO. The fastest-growing birds were not necessarily the most susceptible to lameness on wire flooring, nor did the genders differ in susceptibility in the 2 experiments that included both male and female broilers. The pathogenesis of BCO is not instantaneous, and accordingly, many broilers that did not exhibit lameness, nevertheless, did possess early pathognomonic lesions. These subclinical lesions were equally likely to develop in the right or left leg. The lesion status of the proximal femoral head did not determine the lesion status of the ipsilateral or contralateral proximal tibial head and vice versa. Broilers reared on wire flooring consistently had higher incidences of lameness than hatch-mates reared on wood-shavings litter. Adding probiotics to the diet beginning at 1 d of age consistently reduced the incidence of lameness for broilers reared on wire flooring. These experiments indicate that probiotics administered prophylactically may constitute an alternative to antibiotics for reducing lameness attributable to BCO. Rearing broilers on wire flooring provides an important new research model for investigating the etiology, pathogenesis, and treatment strategies for BCO.

Effects of high dietary levels of soybean meal and its constituents (potassium, oligosaccharides) on foot pad dermatitis in growing turkeys housed on dry and wet litter

Soybean meal (SBM) is the main protein source in diets for turkeys. High dietary levels of SBM are thought to increase the incidence of foot pad dermatitis (FPD). Therefore, this study was conducted to test potential effects of high SBM and to elucidate which constituents in SBM might be associated with the development of FPD. Two week-old female turkeys were allotted to four groups of 29 birds each, and housed on dry wood shavings in floor pens over a period of three weeks. Four different diets were fed: control, high SBM, high potassium (K) or high oligosaccharide (OL) diet. Additionally, for only 8 h/d half of the animals in each group were exposed to wet litter (27% DM) in adjacent separate boxes. The foot pads of all birds were assessed on days 0, 7, 14 and 21 for external lesions. For the histopathology of the foot pads, on day 0 three birds from each group, and on days 7 and 14 six birds per feeding group were selected. The remaining birds in each group were sacrificed on day 21 and their pads were evaluated histologically. High dietary levels of SBM, potassium or oligosaccharides did not influence the severity of FPD on dry litter, but slightly increased the severity on wet litter. However, there were no histopathological differences in FPD severity between these dietary treatments within each litter form compared to the control. Nevertheless, the FPD severity was in general higher on wet litter. Thus, litter moisture appears to be one of the most important factors involved in FPD in turkeys. In addition, all nutritional factors which increase water intake and excreta or litter moisture may contribute to an increased development and severity of FPD in turkeys.

Screening of genes encoding adhesion factors and biofilm formation in Staphylococcus aureus isolates from poultry

Staphylococcus aureus isolates recovered from poultry between 1970 and 1972 (90 old isolates) and in 2006 (81 recent isolates) were screened for the presence of bap, icaA and icaD genes associated with biofilm formation, and for bbp, cna, ebpS, eno, fib, fnbA, fnbB, clfA and clfB genes that encode microbial surface components recognizing adhesive matrix molecules (MSCRAMMs). Most of the old isolates were collected from broiler breeders affected by staphylococcal tenosynovitis and arthritis, whilst nearly all recent isolates were derived from the nose and cloaca of healthy broilers. Ten recent isolates belonged to the animal-associated methicillin-resistant S. aureus (MRSA) ST398. All isolates were positive for clfA, clfB, eno and fnbA, and were negative for bap and bbp. All recent isolates were also positive for ebpS and cna, and all old isolates were positive for fib. The average number of genes encoding adhesins and biofilm-associated proteins in both groups was eight per isolate. All MRSA ST398 isolates in this study were positive for icaD, cna, ebpS, eno, fnbA, fnbB, clfA and clfB. No relevant differences were found between the presence of adhesin and biofilm formation genes in old and recent S. aureus isolates or in isolates from healthy compared with diseased chickens. From this study, there is no indication that the presence of these genes has changed over time and no specific association could be found between the presence of certain MSCRAMM or biofilm genes in poultry S. aureus isolates and the isolate's capacity to cause disease.

Validation of broiler chicken gait scoring training in Thailand, Brazil and New Zealand

Broiler chickens are the most numerous terrestrial farmed animals on earth. These birds can suffer a range of pathologies which result in lameness, and one technique for assessing the impact of lameness on the individual bird, and on the flock has been gait scoring. This paper describes a study where the results of the same training programme for validated gait scoring are compared for groups of assessors in Thailand, Brazil and New Zealand. A uniform course of training carried out in the classroom, through video assessment and through on-farm training was carried out in the countries named; a total of 95 persons being trained overall. A measure of agreement with the reference scale for the assessors' numerical responses was carried out using a Cohen's Kappa test, and the results indicated significant differences in the ‘origin position’ ie the view taken by the assessors of the impact of lameness on the bird before training had taken place, but a high degree of consistency in the response to training. The study demonstrated that gait scoring can be learned by assessors from different geographical and social backgrounds, and that the ‘rate of learning’ – the improvement in performance in relation to a standard, was similar between the countries studied. The ‘origin’ and ‘final’ position of the assessors pre- and post-training, from the different countries in relation to the reference standard is discussed.

Can a Modified Latency-to-Lie Test be Used to Validate Gait-Scoring Results in Commercial Broiler Flocks?

Bodily contact with water is a novel and aversive experience for broiler chickens, and this has been used when designing the Latency to Lie (LTL) test. The original testing procedure, in which the birds are tested in groups, involves a certain settling period, which makes the test time-consuming to carry out on commercial broiler farms. Our modifications of the LTL test for on-farm use mean that a) the birds are tested individually without visual contact with other birds; and b) the water tub is already filled with water when the birds are placed in it. The results from the LTL tests can then be compared with the scores achieved for each individual bird on the commonly used ‘gait scoring’ procedure. At 14 farms participating in a larger survey, we used three birds of each gait score from 0 to 4 (when available) for LTL testing. The time spent standing before making the first attempt to lie down was recorded. The results show a clear negative correlation (r = -0.86, P < 0.001) between time spent standing and gait score. The mean LTL values for the different gait scores were all significantly (P < 0.01) different. There was no significant difference in LTL results between flocks. The method described appears to be well suited for on-farm use. If further developed, it could become a useful tool in monitoring programmes for the ongoing efforts aiming at decreasing the levels of leg weakness in modern broiler production.

Differences in the Expression of Genes in Lame and Normal Broiler Chickens Identified by Subtraction Hybridisation

In the UK, broiler chickens are normally slaughtered at about six weeks of age when they weigh approximately 2.2 kg; this contrasts with the growth of an ‘unimproved’ traditional strain of bird such as a White Sussex, which would weigh about 800 g at the same age. Lameness, characterised by abnormal gait, posture and impaired walking ability, can be prevalent in these rapidly growing birds and has been highlighted as a major welfare concern. It is during the later stages of rearing, when the bird is becoming heavy and may be achieving weight gains of over 50 g per day, that lameness begins to have an economic and welfare impact on the flock and to compromise the behaviour of large numbers of birds. A study was carried out to identify potential differences in the expression of genes between groups of lame and normal broiler chickens using subtraction hybridisation. The first group comprised lame birds with measurable gait abnormalities, and the second group comprised sound (not lame) birds. Both populations came from within the same flock. After extraction of mRNA and creation of cDNA, subtractive hybridisation was performed to eliminate genetic sequences common to both populations. The resultant DNA was separated and presented for sequence data analysis and comparison with a large sequence database. Some examples of the subtracted sequences detected are given, and the potential significance of these sequence differences at the individual and group level is discussed.

Dehydration and Lameness in a Broiler Flock

A case study is described in which a high incidence of lameness in broiler chickens (Gallus gallus domesticus) is associated with rearing to 84 days of age; broilers are normally slaughtered at less than 50 days of age. A sample of 185 birds was scored for walking ability, and 24 birds from this group were assessed for dehydration by measuring plasma osmolality. The proportion of the group having gait abnormalities was compared with that recorded during a recent survey of Danish flocks and was found to be higher. A relationship is established between the degree of gait impairment and the level of dehydration. The degree of dehydration is related to the findings for plasma osmolality from previous research, and the results indicate that some of the birds in this case may have been deprived of access to water for periods in excess of 60 hours.

Relationships in broiler chickens between lameness, liveweight, growth rate and age

Thirteen genotypes of poultry were selected to represent a wide range of growth profiles and were fed either a non-limiting or Label Rouge diet. The birds' degree of lameness and liveweight were measured after 54 and 81 days. The birds reared on the Label Rouge diets were less lame than birds of the same genotype reared on the non-limiting diet. More traditional and slower growing genotypes tended to be less lame than the modern genotypes reared on the same feeding regimen. All the birds, irrespective of their genotype or diet, were less lame after 54 days than after 81 days. However, when liveweight was included in the analysis as a covariable, many of the differences disappeared. Only age at assessment significantly affected the walking ability of the birds, with the birds being approximately 0.6 units of gait score worse at 54 days of age than at 81 days. The regression coefficient between gait score and liveweight was 1.262 at 54 days and 1.128 at 84 days. The results indicated that liveweight was an important determinant of lameness in the diverse range of genotypes examined, that growth rate was also an important determinant of lameness and that younger birds may be more sensitive to differences in liveweight than older birds.

Effects of age and stocking density on leg weakness in broiler chickens

The effects of stocking density (STD) on leg weakness in broiler chickens was assessed in two trials. The interaction between age and STD on leg weakness was further evaluated in one trial. In Trial 1, walking ability was assessed at 28, 42, and 49 d of age. Birds were stocked at 833, 625, or 435 cm2 per bird. In Trial 2, birds were stocked at 625 or 455 cm2 per bird and assessed for tibial dyschondroplasia (TD) by radiographic examination at 28 d and walking ability at 35 d. Foot pad burn, hock burn, and angulation of the hock joint were also assessed at slaughter on Day 42. Body weight was measured during both trials. At 4 wk of age, leg weakness was a relatively minor problem; few severely lame birds had a gait score (GS) of 4 or 5 at any density. However, 2 wk later, the birds had substantially poorer walking ability. Further deterioration had occurred by 7 wk of age. At all ages, males exhibited greater leg weakness than did females, and the proportion of severely lame birds increased with age of assessment. The effect of STD was consistent across both trials; higher STD were associated with poorer walking ability and reduced live weights. In Trial 2, higher STD resulted in more foot and hock burns. Females were more sensitive to STD than were males However, there was no effect of STD on the prevalence of TD or angulation of the hock joint. The effect of high STD on walking ability was apparent even at 4 wk of age. Adjusting the observations for differences in BW did not alter the findings. It was concluded that the lower STD substantially reduced the prevalence of leg weakness.