Master of Science / Department of Clinical Sciences / Michael W. Sanderson / Escherichia coli O157:H7 has emerged as a significant human food-borne pathogen over the past two decades. While cattle have been identified as the major reservoir of the pathogen, the dynamics of shedding are still largely unknown. The role immunosuppression may play on fecal shedding in cattle is explored. The first study determined whether immunosuppression induced by dexamethasone injections affects the level and duration of fecal shedding of E. coli O157. Six one week old Holstein bull calves were injected intramuscularly with dexamethasone and orally inoculated with 109 CFU of a mixture of three nalidixic-acid resistant strains of E. coli O157. Another five one week old Holstein bull calves, only inoculated with the E. coli O157, served as controls. All calves were necropsied and samples from the gastrointestinal tract were cultured. Dexamethasone treated calves shed at higher levels on days four and seven post-inoculation, but not thereafter. The data from this study suggest that there may be a time dependent correlation between dexamethasone immunosuppression and the concentration of E. coli O157 an animal will shed in the feces and that transient immunosuppression does not result in prolonged shedding of E. coli O157. The goal of the second study was to determine whether calves immunosuppressed by persistent infection with bovine viral diarrhea virus (BVDV) will shed E. coli O157 at a higher level and for a longer duration than a normal animal. Nine six to eight week old calves persistently infected with non-cytopathic BVDV and eight normal calves obtained from separate cow-calf operations were orally inoculated with 109 CFU of a mixture five nalidixic-acid resistant strains of E. coli O157. All calves were necropsied and samples from the gastrointestinal tract cultured. There was no statistical difference in the concentration of E. coli O157 shed or the duration of shedding between the persistently infected BVDV calves and the control calves throughout the length of the study. The data suggest that immunosuppression caused by persistent infection with non-cytopathic BVDV infection does not play a role in the level or duration of shedding of E. coli O157:H7 in calves.

Master of Science / Department of Clinical Sciences / Walter C. Renberg / Objective: To measure strain in vivo in the calcanean tendon during trotting in canines, and to compare to strain present after tibiotarsal immobilization. Animals: 6 canines Procedures: A Differential Variable Reluctance Transducer[superscript]TM (DVRT®) strain gauge was surgically implanted on the common gastrocnemius tendon. Surface EMG, % strain, and ground reaction forces were measured prior to intervention and after immobilization. Peak vertical force (Fz), vertical impulse, initial, maximum and final strain, and peak-to-peak EMG amplitude were recorded. Data was analyzed using repeated measures analysis of variance and paired t-tests (p[equal to or less than]0.05). Results: Timing of strain data correlated closely to the hind limb footstrike and EMG activity in all dogs. Maximum tendon strain occurred simultaneous with peak Fz. Continued muscle contraction was evident after immobilization. There was no statistical difference in maximum strain after immobilization compared to normal motion. Minimum strain, both at the beginning and end of the strain curve, was significantly decreased with the immobilized state compared to non-immobilized joints. Conclusions and Clinical Relevance: Tibiotarsal immobilization did not eliminate calcaneal tendon strain during weight bearing. Decreased isometric muscle contraction during swing phase of the gait would account for smaller minimum strain in immobilized joints. Immobilization is frequently applied after Achilles tendon rupture to alleviate strain and force on the sutured repair, with possible complications due to the immobilization method. Direct correlation of strain with tendon force was not made in this study. This would be an important factor before adjusting current treatment recommendations.

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Doctor of Philosophy / Department of Diagnostic Medicine/Pathobiology / Daniel U. Thomson / Escherichia coli O157:H7 is responsible for over 70,000 cases of human illness every year in the United States. Most cases occur in children under the age of five, the elderly, or other immune-compromised people. A small percentage of these cases will develop a life threatening complication, hemolytic uremic syndrome. Cattle are the reservoir host for E. coli O157:H7 and serve as the main source of contamination of meat products and other food sources. The beef cattle industry is diverse with producers caring for as few as one to as many as thousands of cattle. The first objective of this research was to examine three major production systems (conventional, organic, and natural) in the U.S. and the published performance effects of the various technologies used in each system. The second objective was to determine if a newly licensed E. coli O157:H7 SRP® (SRP) vaccine administered to cows pre-partum could achieve successful passive transfer in their offspring. The third objective was to determine if colostrum obtained from SRP vaccinated heifers could protect against an oral challenge with an E. coli K99+ strain. The fourth objective was to examine the shedding characteristics, health, and performance effects of calves born to SRP-vaccinated cows that also receive SRP vaccination themselves. The technologies used in conventional beef cattle production resulted in significant improvements in health and performance of beef cattle. Vaccinating cows pre-partum with SRP resulted in passive transfer in calves consuming their colostrum. Calves that achieved successful passive transfer shed less E. coli K99+ and had improved fecal consistency compared to placebo. When calves were vaccinated with SRP at branding, weaning, and arrival to the feedyard there was no difference in fecal E. coli O157:H7 shedding on arrival to the feedyard or at harvest. Vaccinating calves with SRP had no effects on performance or health outcomes. Vaccinating cattle with SRP may provide protection against other pathogenic E. coli strains and warrants further investigation. The timing of vaccination appears to be an important consideration in order to ensure maximum vaccine efficacy.

Doctor of Philosophy / Department of Diagnostic Medicine/Pathobiology / Derek A. Mosier / The bovine respiratory disease complex (BRDC) is a major concern for cattle producers in the United States and worldwide. One of the most costly and deadly components of BRDC is bovine pneumonic pasteurellosis (BPP) caused by Mannheimia haemolytica. The initial pulmonary inflammation associated with BPP is a characteristic serofibrinous exudation into the lung, which is believed to be induced by M. haemolytica virulence factors such as lipopolysaccharide (LPS) and leukotoxin (LKT) and host cytokines and chemokines such as tumor necrosis factor – α, interleukin – 1β, and interleukin – 8. However, these pulmonary changes often occur before virulence factors or cytokines are substantial components of the pulmonary microenvironment. Other proinflammatory molecules such as substance P (SP) may be involved in the pathogenesis of the peracute serofibrinous exudation of BPP. SP is an 11 amino acid long neuropeptide that is a neurotransmitter of pain that can be released from sensory nerves into tissues to cause neurogenic inflammation. Neurogenic inflammation is characterized by serofibrinous exudation and leukocyte activation. SP-like immunoreactivity was present in the airways, alveolar septa, macrophages, endothelium, and peribronchial nerves in both pneumonic and normal bovine lung; however, SP-like immunoreactivity was increased in pneumonic compared to normal bovine lung due to increased immunoreactivity in macrophages. SP and the combination of SP with histamine and LPS increased the permeability of a calf pulmonary arterial endothelial cell line to Evans blue dye labeled albumin by 12.34%, 13.57%, and 22.03%, respectively compared to a cell control. Similarly, SP and the combination of SP and histamine increased the monolayer permeability of a bovine adrenal gland capillary endothelium by 8.27% and 16.69% compared to a cell control. The increase in permeability was due to endothelial cell shape change and the formation of intercellular gaps rather than cell death. However, SP does not increase the surface expression of the β2 integrin CD18 (the M. haemolytica LKT receptor) on bovine neutrophils nor does it increase LKT-induced leukocytotoxicity of bovine peripheral blood leukocytes. These findings indicate that SP may be a contributor to BPP in association with other cytokines.

Doctor of Philosophy / Department of Diagnostic Medicine/Pathobiology / David G. Renter / Bradley J. White / The objective of my research was to generate novel information concerning the epidemiology, diagnosis and prevention of bovine respiratory disease complex (BRDC), a common pre-weaning and post-weaning beef calf disease. To reach my objective, I conducted three prospective field trials within post-weaned calf populations, and one retrospective study of pre-weaned calves utilizing survey data. I evaluated differences in behavior, health and performance in calves receiving multiple component health programs. Calves in a minimally invasive program, which included primarily non-injectable products, displayed less aversion to initial product administration but experienced higher BRDC morbidity (P = 0.02) and poorer performance (P = 0.04) compared to calves in a more invasive (all injectable products) program. Secondly, in a study of Mannheimia haemolytica inoculated calves, I found that no parameter included in physical examinations, or common blood component evaluations could discern health from disease. However, disease recognition was aided by the measurement of the number of steps taken by a calf in a 24 hour period. None of the parameters that were evaluated predicted the severity of lung pathology. Thirdly, I conducted a study in post-weaned feeder calves that determined prevalence estimates for Mollicutes in general, and Mycoplasma bovis specifically, and their respective associations with health and performance. Nasal Mollicutes prevalence was high on arrival, and differences in calf performance were associated with (P < 0.01) nasal prevalence. More than half of the calves seroconverted to M. bovis; calves not seroconverting gained more weight (0.49 kg/head/day) during the study than those calves that did seroconvert (0.35 kg/head/day). Finally, I conducted a retrospective analysis of national U. S. cow-calf survey data to identify herd level management practices associated with pre-weaned calf BRDC. I found feeding antibiotics to pre-weaned calves, importing cattle, the number of outside visitors, economic purpose of the cow-calf operation, and breeding management of the herd were associated with herd-level pre-weaning BRDC rates. My research projects generated unique information concerning the epidemiology of important pathogens, differences among preventive health programs, objective BRDC diagnostic parameters, and pre-weaning BRDC risk factors. These research studies reinforce the complexity of BRDC and demonstrate the pathogen, animal and management factors affecting BRDC risk in pre- and post-weaned beef calves.

Master of Science / Department of Clinical Sciences / James K. Roush / Objective – To evaluate the value of thermography in a clinical setting for dogs with thoracolumbar disease. Animal Population – Thirteen client-owned short-haired Dachshunds presented to Kansas State University Veterinary Medical Teaching Hospital for paraparesis/paraplegia and diagnosed with thoracolumbar disease via myelogram/CT and confirmed during surgical decompression. Procedures - Thermal images were obtained with a hand-held infrared camera with a focal plane array uncooled microbolometer. Images were obtained after physical exam and client consultation and prior to any pre-anesthetic medications, approximately 30+ minutes after entering the hospital. Additional images were obtained in the same manner at 24 hour intervals following surgery until discharge. Six regions of interest (ROI) were identified and recorded. The ROIs identified were right and left thoracic, lumbar and pelvic regions. From each of these regions average temperatures were taken. Results - Temperatures in the pelvic region were significantly cooler (p< 0.001) over all days as compared to the thoracic and lumbar regions and to the overall mean temperature. The lumbar region temperature was significantly greater on day 0 as compared to thoracic and pelvic regions but was not significantly different on any of the following days. The thoracic temperatures were significantly greater than the lumbar and pelvic regions on day 2 but there was no significant difference on any of the preceding or following days. There was no significant difference between left and right on any of the days. There was a correlation of the pelvic region temperatures on day 3 in relation to the presenting neurological grade. Conclusion - Although there were varied heat patterns detected in dachshunds with IVDD, these patterns did not correlate with neurological grade, lesion site or lateralization of the lesion. Although there was a correlation between neurological grades and the pelvic region temperatures on day 3, this time period is unlikely to provide clinical utility. Clinical Relevance - The results of this study suggest that thermography is not a useful tool for the diagnosis or prognosis of thoracolumbar disease in dogs in a clinical setting.