Stress-induced colibacillosis and turkey osteomyelitis complex in turkeys selected for increased body weight

In vivo models of Escherichia coli infection in poultry

Escherichia coli represents a significant challenge to the poultry industry due to compromised animal welfare, vast productivity losses, elevated mortality, and increased use of antimicrobial compounds. Therefore, effective preventive strategies and insight into the pathogenesis and disease mechanisms of colibacillosis are essential to secure a healthy poultry production. Consequently, discriminative in vivo models of colibacillosis are prerequisite tools for evaluating e.g., preventive measures, exploring novel treatments and understanding disease development. Numerous models of colibacillosis are applied for experimental studies in poultry. Yet, few studies provide a proper characterisation of the model enabling other authors to reproduce experiments or use the model in general. The present paper provides a literature review on avian in vivo models of primary colibacillosis.

Typhlitis induced by Histomonas meleagridis affects relative but not the absolute Escherichia coli counts and invasion in the gut in turkeys

Unlike in chickens, dynamics of the gut microbiome in turkeys is limitedly understood and no data were yet published in context of pathological changes following experimental infection. Thus, the impact of Histomonas meleagridis-associated inflammatory changes in the caecal microbiome, especially the Escherichia coli population and their caecal wall invasion in turkeys was investigated. Birds experimentally inoculated with attenuated and/or virulent H. meleagridis and non-inoculated negative controls were divided based on the severity of macroscopic caecal lesions. The high throughput amplicon sequencing of 16SrRNA showed that the species richness and diversity of microbial community significantly decreased in severely affected caeca. The relative abundances of operational taxonomic units belonging to Anaerotignum lactatifermentans, E. coli, and Faecalibacterium prausnitzii were higher and paralleled with a decreased abundances of those belonging to Alistipes putredinis, Streptococcusalactolyticus, Lactobacillus salivarius and Lactobacillus reuteri in birds with the highest lesion scores. Although the relative abundance of E. coli was higher, the absolute count was not affected by the severity of pathological lesions. Immunohistochemistry showed that E. coli was only present in the luminal content of caecum and did not penetrate even severely inflamed and necrotized caecal wall. Overall, it was demonstrated that the fundamental shift in caecal microbiota of turkeys infected with H. meleagridis was attributed to the pathology induced by the parasite, which only led to relative but not absolute changes in E. coli population. Furthermore, E. coli cells did not show tendency to penetrate the caecal tissue even when the intestinal mucosal barriers were severely compromised.

High Molecular Weight Polymer Promotes Bone Health and Prevents Bone Loss Under Salmonella Challenge in Broiler Chickens

As a consequence of rapid growth, broiler chickens are more susceptible to infection as well as bone fractures that result in birds being culled. Intestinal infection/inflammation has been demonstrated to promote bone loss in mice and humans. Given this link, we hypothesize that therapeutics that target the gut can benefit bone health. To test this, we infected broiler chickens (7 days old) with Salmonella and treated the birds with or without MDY, a non-absorbable mucus supplement known to benefit intestinal health, from day 1–21 or from day 14–21. Chicken femoral trabecular and cortical bone parameters were analyzed by microcomputed tomography at 21 days. Birds infected with Salmonella displayed significant trabecular bone loss and bone microarchitecture abnormalities that were specific to the femoral neck region, a common site of fracture in chickens. Histological analyses of the chicken bone indicated an increase in osteoclast surface/bone surface in this area indicating that infection-induced bone resorption likely causes the bone loss. Of great interest, treatment with MDY effectively prevented broiler chicken bone loss and architectural changes when given chronically throughout the experiment or for only a week after infection. The latter suggests that MDY may not only prevent bone loss but reverse bone loss. MDY also increased cortical bone mineral density in Salmonella-treated chickens. Taken together, our studies demonstrate that Salmonella-induced bone loss in broiler chickens is prevented by oral MDY.

Ascorbic Acid Differentially Affects Stress Response and Resistance to Colibacillosis in Turkeys from Genetic Lines Differing in Growth Rate

Genetic selection for fast growth can affect the ability of male turkeys to cope with stressors, resulting in decreased immunity to opportunistic bacterial infection. The purpose of the current study was to compare the effects of ascorbic acid (AA) on the stress response and resistance to Escherichia coli challenge of birds selected for increased 16-wk body weight (BW; F-line) with their random-bred parent line (RBC2). Male turkeys were raised in duplicate floor pens in a two line×two AA treatment×two stress challenge (SC) design. At 5 wk of age, AA (1200 ppm) was provided in drinking water for a 24-hr period, during which all birds were weighed. After AA treatment, the SC group was subjected to a transport stress protocol. Six hours after the start of transport, SC birds were also inoculated in the thoracic air sac with 1×10(4) colony-forming units of E. coli. The following morning four birds from each pen were bled, and all birds were weighed and necropsied 2 days later. BW and gain after SC were decreased in the F-line but not the RBC2 line, and there were no AA effects on BW. The weight of the bursa of Fabricius relative to BW was higher in the RBC2 line than in the F-line, was decreased by SC, and was not affected by AA. The heterophil∶lymphocyte ratio was higher in the SC F-line as compared to the SC RBC2 and was decreased by AA only in the SC F-line. Corticosterone (C) levels were increased by SC only in the F-line, and AA decreased C levels only in the RBC2 line. Airsacculitis scores were increased in the F-line SC birds. The challenge strain of E. coli was only detected in the air sac and liver of the AA-treated F-line SC birds and in the liver of the no-AA F-line birds. These results suggest that SC at 5 wk of age had a more deleterious effect on the fast-growing F-line than on its parent line and that AA may have increased susceptibility to colibacillosis in the SC F-line birds.

Effect of dexamethasone on bacteriostatic activity of turkey monocytes and implications for food safety

Stress has been shown to affect the immune system of turkeys making them more susceptible to bacterial infections. Five-week-old male and female turkeys were treated with 3 intra-muscular injections of dexamethasone (Dex) at 0, 0.5 and 2.0mg/kg body weight. Twenty-four hours after the third injection birds were bled and white blood cell (WBC) differentials and bacteriostatic activity of monocytes were measured. Dex at both 0.5 and 2.0mg/kg decreased phagocytic activity in females only. Bacteriostatic activity was decreased at both concentrations of Dex at 8 and 16 h post-infection in both sexes and was lower in males as compared to females. Total WBC counts were increased in females at both concentrations of Dex whereas male total WBC counts were unaffected. Both males and females had an increase in the heterophil to lymphocyte ratio. Within the same study, replicate pens of turkeys were challenged with intra-air sac inoculation of 100 cfu of Escherichia coli. Isolation of E. coli was significantly increased by both Dex and E. coli challenge, but there were no differences between sexes. These results suggest that stress can compromise the bacteriostatic activity of turkey monocytes and increase bacterial colonization of blood and tissues, potentially affecting food safety.

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.

Dexamethasone immunosuppression resulting in turkey clostridial dermatitis: a retrospective analysis of seven studies, 1998-2009

We have studied the etiology of turkey osteomyelitis complex (TOC) for the past 20 yr and have determined that this syndrome is caused by the inability of some fast-growing male turkeys to cope with production stressors. Although immunosuppressive viruses have often been associated with susceptibility to gangrenous dermatitis (cellulitis), we hypothesize that production stressors alone can also undermine resistance to opportunistic pathogens by both increasing bacterial translocation from the intestine and disrupting the skin's antimicrobial barrier, resulting in subcutaneous lesions referred to as cellulitis and recently named turkey clostridial dermatitis (CD). Some common characteristics between TOC and CD are that they are both caused by opportunistic bacterial species that are prevalent in the environment and are both most common in adolescent male birds. In both diseases the affected birds are often large, healthy, and from the best-performing flocks. Our TOC studies using dexamethasone immunosuppression result in a high incidence of cellulitis lesions in dead turkeys that were given either Escherichia coli or Staphylococcus aureus respiratory challenges. The natural presence of Clostridium spp. in the poultry intestine and environment suggests that they may also have been concomitant pathogens. We suggest that a useful and repeatable model for CD can be developed by focusing on the ability of stress to increase diuresis and wet litter conditions and undermine both intestinal and cutaneous bacterial resistance in fast-growing male turkeys.

Response of restraint stress-selected lines of Japanese quail to heat stress and Escherichia coli challenge

Japanese quail selected for divergent corticosterone response to restraint stress were evaluated for their susceptibility to heat stress and challenge with Escherichia coli. These quail lines are designated as high stress (HS), low stress (LS), and the random-bred control (CS) lines. Heat stress (35°C, 8 h/d) began at 24 d until the end of the study at 39 d. Birds were challenged with an aerosol spray containing 2 × 10(9) cfu of E. coli at 25 and 32 d. At 38 d, the surviving birds were necropsied and the intestinal tract was screened for both Salmonella and Campylobacter. Body weights of the CS birds were higher than both HS and LS at 17, 25, and 32 d. At 32 d, there was no difference in mortality between males and females and the CS line had higher mortality compared with the LS line with the HS line being intermediate. At 38 d, females of the CS line that were both heat stressed and challenged had a mortality incidence of 25%, which was significantly higher than male birds of the same line and treatment (5.3%). There was an increased incidence in Salmonella enterica serotype Agona isolation after heat stress, with the LS birds having less isolation than the HS birds. Mean corticosterone levels of male birds were not significantly affected by line, heat stress, or E. coli challenge; however, the LS line subjected to heat stress had one-third the level of the HS line, a difference identical to that seen in the original selection for response to restraint stress.

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.

Bone circulatory disturbances in the development of spontaneous bacterial chondronecrosis with osteomyelitis: a translational model for the pathogenesis of femoral head necrosis

This review provides a comprehensive overview of the vascularization of the avian growth plate and its subsequent role in the pathogenesis of bacterial chondronecrosis with osteomyelitis (BCO, femoral head necrosis). BCO sporadically causes high incidences of lameness in rapidly growing broiler (meat-type) chickens. BCO is believed to be initiated by micro-trauma to poorly mineralized columns of cartilage cells in the proximal growth plates of the leg bones, followed by colonization by hematogenously distributed opportunistic bacteria. Inadequate blood flow to the growth plate, vascular occlusion, and structural limitations of the microvasculature all have been implicated in the pathogenesis of BCO. Treatment strategies have been difficult to investigate because under normal conditions the incidence of BCO typically is low and sporadic. Rearing broilers on wire flooring triggers the spontaneous development of high incidences of lameness attributable to pathognomonic BCO lesions. Wire flooring imposes persistent footing instability and is thought to accelerate the development of BCO by amplifying the torque and shear stress imposed on susceptible leg joints. Wire flooring per se also constitutes a significant chronic stressor that promotes bacterial proliferation attributed to stress-mediated immunosuppression. Indeed, dexamethasone-mediated immunosuppression causes broilers to develop lameness primarily associated with avascular necrosis and BCO. Prophylactic probiotic administration consistently reduces the incidence of lameness in broilers reared on wire flooring, presumably by reducing bacterial translocation from the gastrointestinal tract that likely contributes to hematogenous infection of the leg bones. The pathogenesis of BCO in broilers is directly relevant to osteomyelitis in growing children, as well as to avascular femoral head necrosis in adults. Our new model for reliably triggering spontaneous osteomyelitis in large numbers of animals represents an important opportunity to conduct translational research focused on developing effective prophylactic and therapeutic treatments.

Understanding stress-induced immunosuppression: exploration of cytokine and chemokine gene profiles in chicken peripheral leukocytes

At present, the poultry meat and egg industry has gained a lot of ground, being viewed as a provider of a healthy alternative to red meat and other protein sources. If this trend is to be maintained, solutions must be found to improve resistance of chickens to disease, which often is weakened by stressful conditions. In poultry, stress-induced immunosuppression is manifested by failures in vaccination and increased morbidity and mortality of flocks. Currently, several modern cellular and molecular approaches are being used to explore the status of the immune system during stress and disease. It is likely that these new techniques will lead to the development of new strategies for preventing and controlling immunosuppression in poultry. Using quantitative reverse transcription-PCR assays, a broad spectrum of cytokine, chemokine, and their receptor genes can be quantified in birds and then be used as markers to assess the effects of stress on the immune system. Currently, we are investigating immune and endocrine interactions in the chicken, in particular the cells and molecules that are known to be involved in such interactions in mammals. We have evaluated the effects of corticosterone administration in drinking water on peripheral lymphocyte and heterophil cytokine and chemokine gene profiles. In particular, there seems to be effects on cytokine and chemokine mRNA expression levels in both lymphocytes and heterophils, especially expression of the proinflammatory cytokines interleukin (IL)-1beta, IL-6, and IL-18 and chemokines C-C motif, ligand 1 inflammatory (CCLi1); C-C motif, ligand 2 inflammatory (CCLi2); C-C motif, ligand 5 (CCL5); C-C motif, ligand 16 (CCL16); C-X-C motif ligand 1 inflammatory (CXCLi1); and C-X-C motif ligand 2 inflammatory (CXCLi2), which are initially upregulated and are potentially involved in modulating the adaptive immune response. A chronic treatment with corticosterone downregulates proinflammatory cytokines and chemokines, suggesting that the delayed effects of chronic stress can suppress the immune response. Messenger RNA expression levels of transforming growth factor-beta4 (TGF-beta4) are also upregulated in cortisosterone-treated birds. It appears that the balance between T-helper (Th) 1 and Th2/T regulatory cytokine production is altered in conditions associated with significant changes in plasma corticosterone concentration. Experiments are underway to decipher the cytokine and chemokine responses to vaccination and bacterial challenge on the background of stress-induced immunosuppression.

Organic trace minerals and 25-hydroxycholecalciferol affect performance characteristics, leg abnormalities, and biomechanical properties of leg bones of turkeys

Leg problems and resulting mortality can exceed 1% per week in turkey toms starting at approximately 15 wk of age. Dietary supplementation of organic trace minerals (MIN) and 25-hydroxycholecalciferol (HyD) may improve performance, decrease incidence of leg abnormalities, and increase bone strength. Nicholas 85X700 toms were assigned to 4 treatments consisting of a factorial arrangement of 2 concentrations of MIN (0 and 0.1% of Mintrex P(Se), which adds 40, 40, 20, and 0.3 mg/kg of Zn, Mn, Cu, and Se, respectively) and 2 concentrations of HyD (0 and 92 microg/kg of HyD). Diets were formulated to be equal in nutrient content and fed ad libitum as 8 feed phases. Feed intake and BW were measured at 6, 12, 15, 17, and 20 wk of age. Valgus, varus, and shaky leg defects were determined at 12, 15, 17, and 20 wk of age. Tibia and femur biomechanical properties were evaluated by torsion and bending tests at 17 wk of age. There were no treatment effects on BW. Only MIN significantly improved feed conversion ratio through to 20 wk of age. Cumulative mortality at 3 wk of age was greater among the MIN birds, but it was lower by 20 wk (P = 0.085). The MIN decreased the incidence of varus defects at 17 wk of age; shaky leg at 12, 15, and 17 wk of age; and valgus defects at 15, 17, and 20 wk of age. There were no MIN x HyD interaction effects on individual gait problems. Maximum load and the bending stress required for tibias to break in a 4-point assay were increased with MIN supplementation, especially when HyD was also added. Maximum shear stress at failure of femoral bones in a torsion assay was increased by supplementation with both MIN and HyD together. Dietary supplementation of MIN and HyD may improve biomechanical properties of bones. Dietary MIN supplementation may improve feed conversion of turkeys, likely by decreasing leg problems.

Differential Effects of Sex and Genetics on Behavior and Stress Response of Turkeys

Three lines of turkeys were tested for response in T-maze and open-field tests during the first 8 d after hatch, and behavior was observed after catching, moving, and transport. They were also compared for corticosterone (CORT) levels and heterophil:lymphocyte ratios (H:L) at 15 wk of age in response to an Escherichia coli challenge followed by transport stress. Large commercial-(COMM) line birds were faster and more active in the T-maze at d 2 than egg-line birds. Male COMM-line birds were faster than male egg-line birds when tested in an open field at d 8. Egg-line birds had more sleeping behavior after moving to a new floor pen as compared with both an intermediate-sized line (F line) and the COMM line. Transport stress increased CORT levels in all 3 lines, and the increase was greater in males compared with females. The egg line had higher basal CORT levels (P = 0.03) and higher levels after transport (P < 0.0001). The H:L ratios were affected by both transport stress and line but not by sex. The H:L ratio was lower in the egg line as compared with both the F line and the COMM line (P < 0.0001), with the COMM line having the greatest increase in response to transport. These data, combined with those from previous studies of these lines, suggest that differences in activity of fast-growing turkeys may be used to select birds that are less susceptible to inflammatory bacterial disease and that the H:L ratio may be more useful than serum CORT in evaluating the deleterious effects of stress.