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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Diagnosis and management of bovine respiratory disease

Amrine, David E. January 1900 (has links)
Doctor of Philosophy / Department of Diagnostic Medicine and Pathobiology / Brad J. White and Robert L. Larson / Bovine respiratory disease (BRD) is the most costly disease of cattle in US feedyards and diagnosis based on clinical signs of illness is challenging. Over the course of five independent studies we evaluated the precision of multiple observers assigning clinical illness scores (CIS) to calves with induced Mycoplasma bovis pneumonia. We also evaluated the accuracy of CIS in relation to lung lesions at necropsy. Agreement among observers over all five studies was slight ({kappa]= 0.16; 95% confidence interval, 0.10 to 0.24) and ranged from 0.10 to 0.21 for individual trials. The accuracy of CIS varied based on the pulmonary consolidation score chosen to represent a truly ill animal. Inflammation associated with BRD can lead to significant pulmonary damage and reduced lung function. Treatment for BRD frequently involves antimicrobial administration and occasionally non-steroidal anti-inflammatory drugs. We evaluated how calves experimentally challenged with Mannheimia haemolytica respond to treatment with flunixin meglumine, alone or in combination with the antimicrobial florfenicol. Individual calf response to bacterial pneumonia was highly variable in this study. None of the changes in serum biomarkers, CBC or chemistry parameters provided reliable indicators of the pulmonary inflammation associated with the mild severity of bronchopneumonia in our study. Metaphylaxis is frequently administered to manage the risk of BRD within cohorts of cattle. We evaluated the impact of metaphylactic antimicrobial administration 10 days prior to experimental Mannheimia haemolytica inoculation to mitigate pulmonary lesions. We found that calves receiving tildipirosin had less lung damage and fewer clinical signs of illness compared to calves treated with tulathromycin or saline. Finally, the ability to predict those animals that would not finish the production cycle normally would provide benefits in effectively managing cattle. We evaluated the ability of classification algorithms to accurately predict an individual calf’s outcome based on data available at first identification of and treatment for BRD. We found accuracy of classifiers was dependent on the data recorded by the feedyard and there are sub-groups of calves within feedyard populations where classifiers were highly accurate. These data suggest the importance of pairing the proper classifier with the data available.
2

The Development and Assessment of a Lung Biopsy Technique for Early BRD Detection

Burgess, Brandy Ann 06 August 2009
The objectives of this project were: 1) to determine if live animal lung biopsy could be used to characterize early pathologic changes in the bovine lung associated with bovine respiratory disease (BRD), 2) determine if specific infectious respiratory pathogens can be identified in association with early pathological changes, and 3) determine whether pulmonary pathology characterized by live animal lung biopsy at arrival and at the time of initial BRD diagnosis was associated with health and production outcomes of feedlot steers in a commercial feedlot.<p> A live animal percutaneous lung biopsy technique was developed to obtain a lung sample from the right middle lung lobe in intercostal space (ICS) 4 using a Bard® Magnum® reusable biopsy instrument and a modified 4-mm (8g) biopsy needle. The lung biopsy procedure was limited to 2 attempts per biopsy time. In the technique development, 34 animals chronically affected with BRD were utilized, 20 animals in the preliminary development followed by 14 additional animals in a commercial feedlot setting. The technique resulted in 1 fatality of 34 steers (2.9%) and lung parenchyma was harvested in 19 of 34 steers (55.9%) chronically affected with BRD. In addition, in the commercial feedlot setting this procedure was determined to take about 20 minutes per animal.<p> The final study was performed on one hundred feedlot steers considered at high risk of developing BRD from twenty pens within a commercial feedlot. Study animals were enrolled in three different groups: sick on arrival (ARR-SA) consisting of 27 study animals and 13 matched control animals; pen pulls with no fever (PP-NF) consisting of 14 study animals and matched 7 controls; and pen pulls with an undifferentiated fever (PP-UF) consisting of 26 study animals and 13 matched controls. Live animal percutaneous lung biopsies were collected from the right middle lung lobe at 3 different times within the first 30 days of the feeding period, about 2 weeks apart. All samples were histopathologically evaluated and were assessed for the presence of <i>Mycoplasma bovis</i>, <i>Mannheimia haemolytica</i>, Histophilus somni and bovine viral diarrhea virus with immunohistochemistry.<p> A total of 295 lung biopsies were performed yielding 210 (71.2%) lung samples that were sufficient for histopathological evaluation. A histopathology score was awarded to each biopsy based on certain histopathological lesions being present. Only 20 lung biopsy samples from 19 animals received a histopathology score (ie, pulmonary lesions were present) with the most common score being a 1 (maximum score is 20). There were too few lung biopsy samples with a histopathology score to reveal any association with subsequent health events.<p> Immunohistochemistry (IHC) was performed on all lung biopsies recovered yielding one lung sample to be positive for both <i>Mannheimia haemolytica</i> and <i>Mycoplasma bovis</i> from the PP-UF group. There were too few positive samples to reveal any association between IHC and histopathology score.<p> A post mortem evaluation was performed by a study veterinarian on all study animals who died or were humanely euthanized due to poor treatment response. In this study only 4 steers died or were euthanized due to poor treatment response and 3 control steers were humanely euthanized. There were too few animals to reveal any association between histopathology score and post mortem diagnosis.<p> On entry into the feedlot, weights between ARR-SA and the PP-UF and PP-NF groups were significantly different (p<0.05). This is likely an effect of the different processing groups of cattle. At study allocation, the body weights of ARR-SA and PP-UF, PP-UF and their matched controls, and PP-NF and their matched controls were also significantly different (p<0.05). This is likely due to the PP-UF and PP-NF groups experiencing illness for a longer period of time resulting in greater weight loss than the ARR-SA animals as well as the control animals, who were not clinically sick.<p> The live lung biopsy procedure utilized in this study did not appear to cause any long lasting adverse effects as the BRD case fatality rates from the study animals were comparable to the overall case fatality rates reported by the feedlot for fall placed calves. In fact, the study animals experienced a decreased fatality rate compared to the feedlots overall fatality rate. This may be due to the study animals inadvertently being monitored more closely as the pen checkers were aware of and participating in the study. On post mortem evaluation there was no evidence of adhesions at the biopsy site. This procedure was performed on 134 feedlot steers resulting in only 2 acute deaths as a direct result of the live animal percutaneous lung biopsy procedure.<p> The results of this study indicate that live animal, percutaneous lung biopsy can be performed safely on feedlot steers in a commercial feedlot with few clinical side effects. In this study there were only 2 fatalities in 134 steers (1.5%) due to the biopsy procedure or 2 fatalities per 349 sampling times (0.6%) This technique did not prove useful either as a diagnostic tool for the determination of early lung pathology in BRD or as prognostic indicator for health and production outcomes. However, this lung biopsy technique may be a useful diagnostic tool for chronic pneumonia assessment.
3

The Development and Assessment of a Lung Biopsy Technique for Early BRD Detection

Burgess, Brandy Ann 06 August 2009 (has links)
The objectives of this project were: 1) to determine if live animal lung biopsy could be used to characterize early pathologic changes in the bovine lung associated with bovine respiratory disease (BRD), 2) determine if specific infectious respiratory pathogens can be identified in association with early pathological changes, and 3) determine whether pulmonary pathology characterized by live animal lung biopsy at arrival and at the time of initial BRD diagnosis was associated with health and production outcomes of feedlot steers in a commercial feedlot.<p> A live animal percutaneous lung biopsy technique was developed to obtain a lung sample from the right middle lung lobe in intercostal space (ICS) 4 using a Bard® Magnum® reusable biopsy instrument and a modified 4-mm (8g) biopsy needle. The lung biopsy procedure was limited to 2 attempts per biopsy time. In the technique development, 34 animals chronically affected with BRD were utilized, 20 animals in the preliminary development followed by 14 additional animals in a commercial feedlot setting. The technique resulted in 1 fatality of 34 steers (2.9%) and lung parenchyma was harvested in 19 of 34 steers (55.9%) chronically affected with BRD. In addition, in the commercial feedlot setting this procedure was determined to take about 20 minutes per animal.<p> The final study was performed on one hundred feedlot steers considered at high risk of developing BRD from twenty pens within a commercial feedlot. Study animals were enrolled in three different groups: sick on arrival (ARR-SA) consisting of 27 study animals and 13 matched control animals; pen pulls with no fever (PP-NF) consisting of 14 study animals and matched 7 controls; and pen pulls with an undifferentiated fever (PP-UF) consisting of 26 study animals and 13 matched controls. Live animal percutaneous lung biopsies were collected from the right middle lung lobe at 3 different times within the first 30 days of the feeding period, about 2 weeks apart. All samples were histopathologically evaluated and were assessed for the presence of <i>Mycoplasma bovis</i>, <i>Mannheimia haemolytica</i>, Histophilus somni and bovine viral diarrhea virus with immunohistochemistry.<p> A total of 295 lung biopsies were performed yielding 210 (71.2%) lung samples that were sufficient for histopathological evaluation. A histopathology score was awarded to each biopsy based on certain histopathological lesions being present. Only 20 lung biopsy samples from 19 animals received a histopathology score (ie, pulmonary lesions were present) with the most common score being a 1 (maximum score is 20). There were too few lung biopsy samples with a histopathology score to reveal any association with subsequent health events.<p> Immunohistochemistry (IHC) was performed on all lung biopsies recovered yielding one lung sample to be positive for both <i>Mannheimia haemolytica</i> and <i>Mycoplasma bovis</i> from the PP-UF group. There were too few positive samples to reveal any association between IHC and histopathology score.<p> A post mortem evaluation was performed by a study veterinarian on all study animals who died or were humanely euthanized due to poor treatment response. In this study only 4 steers died or were euthanized due to poor treatment response and 3 control steers were humanely euthanized. There were too few animals to reveal any association between histopathology score and post mortem diagnosis.<p> On entry into the feedlot, weights between ARR-SA and the PP-UF and PP-NF groups were significantly different (p<0.05). This is likely an effect of the different processing groups of cattle. At study allocation, the body weights of ARR-SA and PP-UF, PP-UF and their matched controls, and PP-NF and their matched controls were also significantly different (p<0.05). This is likely due to the PP-UF and PP-NF groups experiencing illness for a longer period of time resulting in greater weight loss than the ARR-SA animals as well as the control animals, who were not clinically sick.<p> The live lung biopsy procedure utilized in this study did not appear to cause any long lasting adverse effects as the BRD case fatality rates from the study animals were comparable to the overall case fatality rates reported by the feedlot for fall placed calves. In fact, the study animals experienced a decreased fatality rate compared to the feedlots overall fatality rate. This may be due to the study animals inadvertently being monitored more closely as the pen checkers were aware of and participating in the study. On post mortem evaluation there was no evidence of adhesions at the biopsy site. This procedure was performed on 134 feedlot steers resulting in only 2 acute deaths as a direct result of the live animal percutaneous lung biopsy procedure.<p> The results of this study indicate that live animal, percutaneous lung biopsy can be performed safely on feedlot steers in a commercial feedlot with few clinical side effects. In this study there were only 2 fatalities in 134 steers (1.5%) due to the biopsy procedure or 2 fatalities per 349 sampling times (0.6%) This technique did not prove useful either as a diagnostic tool for the determination of early lung pathology in BRD or as prognostic indicator for health and production outcomes. However, this lung biopsy technique may be a useful diagnostic tool for chronic pneumonia assessment.
4

Current and future strategies of bovine respiratory disease diagnostics and treatments

Miller, Shelby Lynn January 1900 (has links)
Master of Science / Department of Diagnostic Medicine/Pathobiology / Alison P. Adams / Bovine respiratory disease (BRD) is the most common and costly disease affecting cattle in the world today. The disease was first described in the late 1800s and is one of the most extensively studied diseases of livestock. BRD accounts for 65 - 80% of the morbidity and 45 - 75% of the mortality in some feedlots. Outbreaks typically occur around 10 days after transportation with the majority of deaths occurring within the first 45 days of arrival. Bacterial pathogens, physiologic stressors, and concurrent viral infections are all important factors causing BRD; other factors include seasonality, heritability, and breed tolerance. Diagnostic and treatment measures are continually being critiqued and researched. Even with continued research and the administration of antibiotics, BRD still continues to be a problem for the beef industry. Remote early detection and previous calf history are two resources that can help feedlots diagnose the disease earlier, or prevent it entirely. Feeding behavior and physical exams of the calves can also aid in early detection. New antibiotics and treatment methods have been developed, but the BRD problem still exists. Since the disease is most problematic in feedlot cattle, treatment of a large number of cattle in this setting can be costly, and often, performance and carcass traits are also affected. New preventative measures will be crucial to the industry with the continued problems and consequences of BRD. Improved treatment options and enhanced diagnostic tools will also be imperative for the control and treatment of BRD in the future.
5

Assessment of On-Arrival Vaccination and Deworming on Health and Growth Performance in High Risk Stocker Cattle

Wagner, Richard Tucker 14 December 2018 (has links)
The study objective was to evaluate the effects of vaccination (respiratory and clostridial vaccination or no vaccination) and deworming (fenbendazole and levamisole or no deworming) of high risk stocker calves on-arrival on health and growth performance. Eighty sale barn origin calves were purchased three separate years (n=240) from local order buyer. Steers (n=61) and bulls (n=179) were received over three days (d -3 to -1). On d 0 calves were stratified by arrival BW and FEC into 20 pens of 4 calves each, and treatment was applied to pens in 2 x 2 factorial. Vaccination increased the likelihood of BRD 1.7 times (P=0.07) versus calves not vaccinated. Vaccination did not affect gain, but calves receiving dewormer had greater ADG than those not receiving dewormer. Calves that arrived uncastrated or with high fever (≥40.0°C) gained less and were 1.7 and 4.3 times more likely (P<0.10) to be treated for disease, respectively.
6

Bovine respiratory disease: understanding how stress modulates immune and growth parameters when cattle are challenged with respiratory pathogens (viral and bacterial)

Falkenberg, Shollie 06 August 2011 (has links)
Bovine respiratory disease (BRD) complex is a multiactorial disease syndrome that results from various individual contributions and interactions of pathogen, host, and environmental/management factors. Despite the efforts in research, prevention and treatment, BRD remains a leading cause of economic loss in the cattle industry. While advances in therapeutics and new vaccines have been developed over the past 20 – 25 years, the incidence of respiratory disease does not appear to be on the decline, rather it is appears to be increasing. While bacterial and viral pathogens, and various stressors associated with BRD have been characterized, there are no animal models that can reproduce similar presentation of symptoms observed for BRD in the industry. Based on the etiology of BRD, a series of projects were designed to provide a better understanding of the individual and multiple contributions for the factors associated with the complex. It is believed that the viral pathogens or stressors can suppress immune defenses allowing opportunistic bacteria the ability to colonize and cause an infection. Therefore, trials investigating the individual contribution that varying doses of infectious bovine rhinotracheitis virus and transportation stress have on cattle were conducted. A final project investigating the combination effect of the bacterial pathogen M. haemolytica and activation of the hypothalamic-pituitaryrenal axis to elicit glucocorticoid release was evaluated. Ultimately, the research projects were designed to build upon each other to understand each component in the etiology of this disease.
7

Transmission dynamics, characterization, diagnosis, and control of Bovine Respiratory Disease

Capik, Sarah F. January 1900 (has links)
Doctor of Philosophy / Department of Diagnostic Medicine/Pathobiology / Robert L. Larson / Brad J. White / The diagnosis and prevention of bovine respiratory disease (BRD) is challenging due to the multifactorial nature of the disease. Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni are gram negative bacteria that are commonly considered three of the most important bacterial agents involved in the etiology of BRD; all three are also commensals in the upper respiratory tracts of healthy cattle. However, despite decades of study, questions still remain regarding the transmission dynamics and characterization of these bacteria, the ability of diagnostic sampling methods to accurately portray the causative bacteria, and ways to mitigate the effects of risk factors for BRD such as long-distance transportation. Through our research, we have demonstrated how variable the culture results of a single nasopharyngeal swab can be and the challenges of using an individual culture to truly represent animal M. haemolytica status. Additionally, comparison of the diagnostic performance of two antemortem sampling methods, nasopharyngeal swabs (NPS) and bronchoalveolar lavages (BAL), revealed high agreement, high negative predictive values of NPS for the presence of M. haemolytica, P. multocida, and H. somni in the lungs, and the potential for different susceptibility profiles from paired NPS and BAL samples. As agreement and predictive values can vary with disease prevalence, interpretation of diagnostic test results should be done carefully and with due consideration of the sample population in which the test is being applied. An investigation into cattle behavior following a relatively innocuous handling procedure indicated that some behaviors are altered after handling and restraint in a squeeze chute. Additionally, we demonstrated that cattle with different temperament scores may have different activity levels and spend different amounts of time within 1 m of the hay bunk, grain bunk, waterer, and shed after handling. Consequently, there is also the potential to improve upon disease detection algorithms by incorporating behavioral changes that may occur after handling events and the need for careful trial design when behavioral parameters are a trial outcome. Additionally, this study indicated that some behaviors may vary for calves that react differently when handled, which also has potential implications when behavior is considered a variable of interest. Examination of the potential for 1 mg/kg oral meloxicam administered pre-transport to mitigate the effects of long-distance transportation revealed that meloxicam did not have a statistically significant effect on the maintenance of leukocyte function or the reduction of inflammation during or after long-distance transportation in healthy steers. Finally, a report on two separate experiments regarding the effects of 1 mg/kg oral meloxicam administered pre-transport on the movement, feeding, and drinking behaviors and performance of transported and non-transported calves demonstrated that there was a significant day effect on behaviors in transported calves but meloxicam did not affect behavior or performance. However, meloxicam did modify the effect of day on daily distance traveled in non-transported calves but there were no significant within-day comparisons between non-transported meloxicam and non-transported control calves. These results do not provide evidence for the benefit of administering a single dose of 1 mg/kg oral meloxicam prior to long-distance transportation.
8

AN EVALUATION OF THE IMPACT OF MANAGEMENT PRACTICE ON THE HEALTH AND WELFARE OF DAIRY HEIFER CALVES

Stanton, Amy Leanne 24 August 2011 (has links)
The objectives of this thesis were to investigate 1) the use of behavior and activity monitoring for the identification of heifers at risk of disease, 2) the use of group level management practices to reduce the risk of disease, and 3) the identification of long-term impacts of bovine respiratory disease complex (BRD). For objective 1, lying posture, a decreased willingness to approach an observer and high lethargy scores were associated with diarrhea in calves under 2 weeks of age and a high lethargy score in 4-6 week old calves was associated with decreased average daily gain (ADG) in the first 8 weeks of life (n = 744). In weaned calves (n = 74) increased activity (increase in steps and decrease in lying), standing at the bunk not eating, and lying far from other calves in the first 3 days post-weaning were associated with decreased post-weaning weight gain. For objective 2, separating social mixing from movement to a novel environment, and administering prophylactic antibiotics to calves at high risk of disease, were investigated. Both mixing and movement to a novel environment increased activity levels in newly weaned dairy calves (n = 64). When calves were mixed prior to movement to a novel environment they had a smaller increase in activity compared to calves that were simultaneously mixed and moved. No differences in weight gain or calf starter intake were observed. Administration of a prophylactic antibiotic, tulathromycin, to 3 day old calves upon arrival at a heifer raising facility (n = 788) and 8 week old calves at first movement to group housing (n = 1,392 ) was found to reduce diarrhea and otitis media, and BRD, respectively. Objective 3 was addressed by monitoring calves that received tulathromycin at 8 weeks of age to determine the long-term impacts of BRD. Bovine Respiratory Disease complex was associated with decreased growth to 9 months of age, decreased survival to first calving, increased risk of dystocia and a greater age at first calving. / Natural Sciences and Engineering Research Council of Canada & Pfizer Animal Health
9

Heat stress detection and mitigation in feedlot cattle

Unruh, Ellen M. January 1900 (has links)
Master of Science in Biomedical Sciences / Department of Clinical Sciences / Robert L. Larson / Bradley J. White / Feedlot cattle frequently endure high environmental temperature-humidity index conditions in the summer months within cattle feeding regions of North America. Heat stress develops when the total heat gain (combined effects of environmental and metabolic factors) exceeds an animal’s heat loss capabilities. The objective of my research was evaluating heat mitigation strategies and developing a practical method to identify animals that are of greatest risk of heat stress; thus improving animal welfare and performance. A number of heat abatement strategies have been utilized in US feedlots including shade, sprinklers, nutritional modifications, and misters. A literature review was performed using published journal articles demonstrated significant benefits of providing shade to feedlot cattle. Sprinkling the pen surface may be just as beneficial as sprinkling or misting cattle. Sprinkling the ground not only cooled the ground which increased the thermal gradient between lying cattle and the ground, but also provided increased thermal conductivity and better heat flow down that gradient. A study was performed to develop a noninvasive, remotely applied, practical method to identify animals at risk for heat stress. Infrared thermography images were obtained during the morning hours and pant scores obtained in the afternoon hours. Data mining techniques were employed to evaluate accuracy of potential classification methods to identify heat stress events in the afternoon based on the known morning data. Using infrared technology as a diagnostic test was not accurate for predicting heat stress events in the study presented. Finally a retrospective study of Kansas feedlot performance, medical and weather data was performed. Findings indicate that diagnostic counts of bovine respiratory disease are associated with elevated ambient temperature two days prior. In conclusion, heat stress in beef feedlot animals is an important area of research. Heat mitigation methods such as shade have been proven to be effective at reducing heat stress in beef feeder cattle. Further research is needed to evaluate the use of infrared technology to predict heat stress events in the feedlot setting.
10

Pasteurella multocida biofilm formation, and the interrelationship of P. multocida with Histophilus somni in a polymicrobial biofilm during bovine respiratory disease

Petruzzi, Briana Lynn 08 February 2018 (has links)
Pasteurella multocida is an important multi-host animal and zoonotic pathogen that is capable of causing respiratory and multi-systemic diseases, bacteremia, and infections resulting from bite wounds. The glycosaminoglycan capsule (CPS) of P. multocida is an essential virulence factor, protecting the bacterium from host defenses. However, chronic infections such as bovine respiratory disease (BRD) and avian cholera may be associated with biofilm formation. Biofilm formation was inversely related to capsule production (determined by uronic acid and N-acetylglucosamine assays), and was confirmed with capsule-deficient mutants of mucoid strains. Capsule-deficient mutants formed biofilms with a larger biomass that was much thicker and smoother than encapsulated strains. Gas chromatography-mass spectrometry, nuclear magnetic resonance, and enzymatic digestion demonstrated that the matrix material of the biofilm was composed predominately of a glycogen exopolysaccharide (EPS). Therefore, CPS may interfere with biofilm formation by blocking adherence to a surface or by preventing the EPS matrix to encase large numbers of bacterial cells. Chemical mutagenesis was performed on P. multocida strain P1059, resulting in isolation of an acapsular mutant designated as P1059-R8. A uridyltransferase encoded by gene P1059_01979 was mutated in such a way that a polar amino acid was changed to a non-polar amino acid near the active site. The protein product of P1059_01979 is important for the biosynthesis of the CPS subunit N-acetylglucosamine. CPS quantification revealed that the subunit glucuronic acid was produced in equal concentrations to the parent, but the CPS subunit N-acetylglucosamine was not detected in the chemical mutant. Biofilm formation in the chemical mutant was significantly higher than in WT P1059 and the capsule-deficient mutant. We hypothesize that P1059_01979 is essential for CPS production in P. multocida serogroup A. Histophilus somni and Pasteurella multocida cause bovine respiratory disease (BRD) and systemic infections in cattle. Following respiratory infection of calves with H. somni, P. multocida is also often isolated from the lower respiratory tract. Because H. somni normally forms a biofilm during BRD, we suspected that P. multocida may co-exist with H. somni in a polymicrobial biofilm. Interactions between the two species in the biofilm were characterized and quantified by fluorescence in situ hybridization (FISH), and the biofilm matrix of each species examined by fluorescently-tagged lectins (FTL), confocal scanning laser microscopy of in vitro biofilms and bovine pulmonary tissue following dual H. somni and P. multocida infection. FISH and FTL were used to show that P. multocida and H. somni were evenly distributed in the in vitro biofilm, and both species contributed to the polymicrobial biofilm matrix. COMSTAT z-stack image analysis revealed that the average biomass and biofilm thickness of the individual and polymicrobial biofilms were greatest when both species were present. Encapsulated P. multocida isolates not capable of forming a biofilm still formed a polymicrobial biofilm with H. somni, but only the EPS of H. somni could be detected by FTL staining of bovine tissues from which both species were isolated. Bacteria within a biofilm are more quiescent than during planktonic growth and induce less of an inflammatory response, indicating encapsulated P. multocida may take advantage of the H. somni biofilm to persist in the host during less severe, but more chronic, BRD. These results may have important implications for the management of BRD. Acute avian cholera is associated with encapsulated P. multocida, while chronic and asymptomatic cases of avian cholera are associated with acapsular P. multocida isolates. We hypothesize that biofilm formation is present and an important factor for chronic and asymptomatic avian cholera. Experimental infections of chickens with biofilm deficient P. multocida strain WT X73, proficient biofilm forming P. multocida strain X73ΔhyaD, and proficient biofilm forming clinical isolates 775 and 756 showed that virulence inversely correlated with biofilm formation. Histopathological analysis showed that biofilm forming isolates induced little inflammation in the lungs, heart, and liver, while biofilm deficient isolates induced greater inflammation. Biofilm material was located in pulmonary tissues of chickens diagnosed with chronic avian cholera using FTL staining.. Quantitative real-time PCR for expression of cytokine genes in the spleens of infected chickens indicated that P. multocida induced Th1 and Th17 immune responses during acute and chronic avian cholera. Chickens that succumbed to acute avian cholera after experimental challenge with WT X73 had high levels of INF-ƴ, IL-1β, IL-6, IL-12A, IL-22, IL-17A, and IL-17RA expression in the spleen compared to all other experimental groups. Antibody titers were low, indicating that antibodies may be less important in managing and clearing P. multocida infections. / Ph. D.

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