Comparison of bronchoalveolar lavage fluid obtained from Mannheimia haemolytica-inoculated calves with and without prior treatment with the selectin inhibitor TBC1269

OBJECTIVES: To determine effects of selectin inhibitor TBC1269 on neutrophil infiltration, and neutrophil-associated injury during pneumonia induced by Mannheimia haemolytica and concentration of antimicrobial anionic peptide (AAP) in bronchoalveolar lavage fluid (BALF) as well as antimicrobial activity of BALF from healthy (control) neonatal calves, neonatal calves with M haemolytica-induced pneumonia, neonatal calves with prior treatment with TBC1269, and adult cattle. ANIMALS: Eighteen 1- to 3-day-old calves and 9 adult cattle. PROCEDURE: Calves were inoculated with M haemolytica or pyrogen-free saline (0.14M NaCl) solution into the right cranial lung lobe, and BALF was collected 2 or 6 hours after inoculation. Thirty minutes before and 2 hours after inoculation, 4 calves received TBC1269. The BALF collected from 9 adult cattle was used for comparison of BALF AAP concentration and antimicrobial activity. Protein concentration and neutrophil differential percentage and degeneration in BALF were determined. An ELISA and killing assay were used to determine BALF AAP concentration and antimicrobial activity, respectively. RESULTS: Total protein concentration was significantly decreased in BALF from calves receiving TBC1269. Similar concentrations of AAP were detected in BALF from all calves, which were 3-fold higher than those in BALF from adult cattle. However, BALF from neonates had little or no anti-M haemolytica activity. CONCLUSIONS AND CLINICAL RELEVANCE: These results suggest that TBC1269 decreases pulmonary tissue injury in neonatal calves infected with M haemolytica. Although AAP is detectable in neonatal BALF at 3 times the concentration detected in adult BALF, neonatal BALF lacks antimicrobial activity for M haemolytica.     

A selectin inhibitor decreases neutrophil infiltration during acute Mannheimia haemolytica pneumonia

The degree to which the selectin inhibitor TBC1269 reduces neutrophil infiltration in specific microscopic locations of the lung during acute pneumonia of neonates was determined. Neonatal calves were inoculated intrabronchially with Mannheimia (Pasteurella) haemolytica or saline, and lung tissue was collected at 2 and 6 hours postinoculation (PI). One 6-hour group inoculated with M. haemolytica received TBC1269 intravenously before and after inoculation with M. haemolytica. Infiltrates of neutrophils were significantly higher in the alveolar lumen and septae but lower in the bronchial lumen and epithelium at 6 hours PI than at 2 hours PI. Significantly fewer neutrophils (P < 0.05) were present in the alveolar lumen and septae, and the bronchiolar lumen and lamina propria in the lungs of TBC1269-treated calves compared with untreated calves at 6 hours PI. TBC1269 did not alter the infiltration into bronchi and blood vessels or the expression of the selectin-independent adhesion molecule, ICAM-1. This work suggests that during acute pneumonia of neonates 1) neutrophil infiltrates progressively increase in the alveolar lumens and septae but decrease in the bronchial lumen and epithelium with time, 2) TBC1269 reduces neutrophil infiltration into specific regions of alveoli and bronchioles rather than uniformly throughout the lung, and 3) selectin inhibition does not affect the location and intensity of ICAM-1 expression.     

Efficacy of difloxacin in calves experimentally infected with Mannheimia haemolytica

OBJECTIVE: To determine the efficacy of difloxacin, a novel fluoroquinolone antibiotic, in calves experimentally infected with Mannheimia haemolytica (formerly Pasteurella haemolytica). ANIMALS: Seventy-two 3-month-old Holstein calves. PROCEDURES: Calves were inoculated with M haemolytica intratracheally; after they developed clinical signs of pneumonic pasteurellosis, they were randomly assigned to 1 of 6 groups (n = 12/group). Calves in each group were treated with 10% difloxacin (2.5 or 5 mg/kg of body weight), 5% difloxacin (2.5 or 5 mg/kg), enrofloxacin (5 mg/kg), or saline (0.9% NaCl) solution (control group), once daily for 5 days, and clinical signs were scored daily. On day 15, calves were euthanatized, and the percentage of diseased lung tissue was calculated. Swab specimens of the lungs were submitted for bacterial culture. RESULTS: Mortality rate and percentage of diseased lung tissue were significantly higher and cure rate and average daily gain were significantly lower for control calves, compared with calves in the treatment groups; however, no significant differences were found among treatment groups. Mannheimia haemolytica was isolated from the lungs of 10 control calves and from at least 2 calves in each of the treatment groups. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that difloxacin and enrofloxacin were equally effective for treatment of calves with experimentally induced pneumonic pasteurellosis. However, treatment of infected calves with difloxacin or enrofloxacin may not eliminate the organism.     

Effect of bovine granulocyte colony-stimulating factor on the development of pneumonia caused by Mannheimia haemolytica

The role of recruited neutrophils in Mannheimia haemolytica infection is controversial. We hypothesized that the neutrophilia induced by recombinant bovine granulocyte colony-stimulating factor (GCSF) would lead to rapid bacterial clearance and less severe lesions after infection with M. haemolytica. Two experiments (A and B) were conducted in which four calves per experiment were treated daily with 5 microg/kg GCSF and four calves per experiment were treated with saline. All 16 calves were challenged with 5 x 10(9) colony-forming units (cfu)/ml (experiment A) or 4.5 x 10(8) cfu/ml (experiment B) of M. haemolytica bacteria, into the right bronchus by bronchoscope-placed catheter. The mean maximal blood neutrophil counts in non-GCSF-treated and GCSF-treated calves before bacterial challenge were 5.6 +/- 0.7 x 10(9)/liter and 25.4 +/- 2.7 x 10(9)/liter, respectively. Two untreated calves became neutropenic and were euthanatized 2 days after infection because of severe respiratory distress. GCSF-treated calves had a 37% reduction in lung lesions compared with nontreated calves, and this difference was significant (P=0.04) when the effect of previous antibody titre to leukotoxin was considered. The effect of GCSF treatment on the severity of clinical signs seemed to be influenced by the antibody titre to M. haemolytica leukotoxin, although this effect could not be conclusively addressed. In conclusion, GCSF induced neutrophilia and partially protected calves against experimental infection with M. haemolytica. These results imply that increased numbers of neutrophils may, under some circumstances, protect against severe pneumonia caused by M. haemolytica.     

Adenosine-5'-triphosphate release by Mannheimia haemolytica, lipopolysaccharide, and interleukin-1 stimulated bovine pulmonary epithelial cells

Mannheimia haemolytica, one of the agents associated with bovine respiratory disease complex, can cause severe lung pathology including the leakage of vascular products into the airways and alveoli. Previous work by this laboratory has demonstrated that bovine lung endothelial and epithelial cells undergo dramatic permeability increases when exposed to adenosine-5'-triphosphate (ATP). Therefore, we wanted to determine if ATP levels were elevated in bronchoalveolar lavage (BAL) samples from calves experimentally infected with M. haemolytica. In addition, cultured bovine pulmonary epithelial (BPE) cells were stimulated with heat-killed and live M. haemolytica bacteria, lipopolysaccharide (LPS), lipoteichoic acid (LTA), interleukin-1 (IL-1), and zymosan activated plasma (ZAP) to determine whether they might release extracellular ATP during in vitro infection. Calves experimentally exposed to M. haemolytica had an approximately 2-fold higher level of ATP in their BAL samples compared to control. BPE cells exposed to increasing numbers of heat-killed or live M. haemolytica had significantly increased levels of ATP release as compared to time-matched controls. Finally, BPE cells treated with several concentrations of LPS and IL-1 had increases in ATP release as compared to time-matched controls. This increase appeared to be a result of active ATP secretion by the cells, as cell viability was similar between treated and non-treated cells. Neither ZAP nor LTA induced any ATP release by the cells. In conclusion, ATP levels are elevated in lung secretions from calves infected with M. haemolytica. In addition, lung epithelial cells can actively release ATP when exposed to heat-killed or live M. haemolytica, LPS or IL-1.     

Importance of neutrophils in the pathogenesis of acute pneumonic pasteurellosis in calves

Acute lung injury was induced in 24 calves by intratracheal inoculation with Pasteurella haemolytica. Calves in groups 1 and 2 were neutrophil depleted, using hydroxyurea given IV. Group 1 calves (n = 7) were inoculated intratracheally with saline solution, and group 2 calves (n = 7) were inoculated with P haemolytica. Group 3 calves (n = 7) had normal numbers of neutrophils and were inoculated with P haemolytica. Group 4 calves (n = 3) were treated acutely with hydroxyurea IV, had normal numbers of neutrophils, and were inoculated with P haemolytica. After inoculation, calves with normal numbers of neutrophils (groups 3 and 4) became hypoxemic 2 hours after inoculation, and hypoxemia persisted until necropsy (6 hours after inoculation). These calves also developed tachypnea, bradycardia, neutropenia, and lymphopenia. Lung lesions consisted of necrosis of the alveolar walls, intra-alveolar hemorrhage, and a severe exudative and necrotizing bronchopneumonia, with accumulation of proteinaceous fluid in alveoli and lymphatics. In neutrophil-depleted calves (groups 1 and 2), blood gas values, heart and respiratory rates, and numbers of circulating leukocytes did not change after inoculation with saline solution or with P haemolytica. At necropsy, the lungs of neutrophil-depleted calves were grossly normal. Therefore, neutrophils were required for the acute lung injury induced by P haemolytica. The protective effect of neutrophil depletion was a specific effect of hydroxyurea because calves with high circulating concentrations of hydroxyurea and calves with normal numbers of neutrophils (group 4) developed lung injury.     

Cytokine expression by pulmonary leukocytes from calves challenged with wild-type and leukotoxin-deficient Mannheimia haemolytica

The objective of this study was to assess the role of leukotoxin (LKT) in modulating the pulmonary cytokine response of calves challenged with Mannheimia haemolytica. Thirty-six calves, seronegative to LKT and M. haemolytica whole cell antigen were divided into three groups (I, II and III). Calves in groups I and II were challenged by the intra-bronchial route with 25 mL of phosphate buffered saline (PBS) containing 0.44×10(9) cfu/mL of LKT deficient (lkt(-)) and 25 mL of PBS containing 0.31×10(9) cfu/mL of wild-type (wt) M. haemolytica serotype 1, respectively. Group III calves were challenged intra-bronchially with 25 mL of sterile PBS. Leukocytes were collected from broncho-alveolar lavage fluid (BALF) 4 days before and at 1, 3, and 6 days post-inoculation (p.i.). Expression of the following cytokines in the recovered leukocytes was measured using real-time PCR: interleukin (IL)-1β, -8, -10, -12 (p40) and TNF-α. The amount of TNF-α produced was also quantified by ELISA. Although a statistically significant difference in the expression of these cytokines was not observed between groups challenged with the wt and lkt(-) strains, the wt infected group (II) did exhibit higher mean clinical scores. Overall, there was considerable variation in the composition of the BALF between the groups and by day 7 p.i., both lkt(-)- and wt-challenged calves had seroconverted to M. haemolytica.     

In situ expression of intercellular adhesion molecule-1 (ICAM-1) mRNA in calves with acute Pasteurella haemolytica pneumonia.

The in situ expression of intercellular adhesion molecule-1 (ICAM-1) mRNA in normal and pneumonic lung tissues of Holstein calves with bovine leukocyte adhesion deficiency (BLAD) was compared with that of age-matched non-BLAD Holstein calves by in situ hybridization. Twenty-four Holstein calves (both BLAD and non-BLAD) were randomly assigned to one of two experimental groups and inoculated intrabronchially with Pasteurella haemolytica or pyrogen-free saline. Lung tissues were collected and fixed in 10% neutral formalin at 2 or 4 hours postinoculation (PI). The expression and distribution of ICAM-1 mRNA in the different cell types of the lung tissue was detected by in situ hybridization with a 307-base-pair bovine ICAM-1 riboprobe. In lungs of both non-BLAD and BLAD saline-inoculated calves, ICAM-1 expression was present in epithelial cells but occurred in <30% of cells in bronchi, bronchioles, and alveoli. ICAM-1 expression in vascular endothelial cells was present in <30% of cells in pulmonary arteries and veins. The expression of ICAM-1 was significantly greater (>60% of cells) in bronchiolar and alveolar epithelial cells and pulmonary endothelial cells of arteries and veins in both BLAD and non-BLAD calves inoculated with P. haemolytica. Bronchiolar epithelium had the highest intensity of mRNA expression and highest percentage of cells that were stained, whereas bronchial epithelium had the lowest intensity and percentage of cells stained. Most alveolar macrophages and neutrophils in infected lungs also expressed ICAM-1. ICAM-1 expression was generally increased in infected BLAD calves at 2 hours PI as compared with non-BLAD calves but not at 4 hours PI. The increased expression of ICAM-1 during acute P. haemolytica pneumonia in calves suggests that ICAM-1 is upregulated and may play a role in leukocyte infiltration. The extent of ICAM-1 expression in P. haemolytica-inoculated calves with BLAD was initially enhanced but otherwise similar to that in non-BLAD calves.     

Cellular inflammatory response in the lungs of calves exposed to bovine viral diarrhea virus, Mycoplasma bovis, and Pasteurella haemolytica

Three, 5, or 7 days after inoculation with bovine viral diarrhea (BVD) virus (n = 12) or Mycoplasma bovis (n = 12), groups of calves were exposed to aerosols of Pasteurella haemolytica and were euthanatized 4 hours later. Histologic lesions in the lungs and the ratios of neutrophils to alveolar macrophages, collected by bronchoalveolar lavage, were compared with those of clinically healthy calves (n = 8) and calves inoculated with BVD virus only (n = 4), M bovis only (n = 4), or P haemolytica only (n = 2). Inoculation with BVD virus or M bovis did not have a significant (P greater than 0.05) effect on the neutrophil/macrophage ratio in the bronchoalveolar lavage. Aerosol exposure to P haemolytica induced a marked and significant (P less than 0.01) change in the neutrophil/macrophage ratio (from less than 1:9 to greater than 9:1). The reversed neutrophil/macrophage ratio in calves exposed to P haemolytica correlated well with the histologic changes in which small bronchi and bronchioles were plugged with purulent exudate. Inoculation with BVD virus did not induce gross or microscopic lesions in the lungs. Inoculation with M bovis resulted in a severe peribronchial lymphoid hyperplasia with mild exudation of neutrophils and macrophages into the cranioventral parts of the lungs.     

Comparison of pharmacokinetics of danofloxacin and enrofloxacin in calves challenged with Mannheimia haemolytica

OBJECTIVE: To compare concentrations of danofloxacin, enrofloxacin, and ciprofloxacin in plasma and respiratory tissues of calves treated after challenge with Mannheimia haemolytica. ANIMALS: 75 calves. PROCEDURE: 24 hours after challenge with M. haemolytica, 72 calves with clinical signs of respiratory tract disease were randomly assigned to 1 of 12 equal treatment groups.Three nonchallenged, nontreated calves formed a control group. Challenged calves were treated with danofloxacin (6 and 8 mg/kg, SC) and enrofloxacin (8 mg/kg, SC) once. At 1, 2, 6, and 12 hours after treatment, 6 calves from each treatment group were euthanatized. Antimicrobial drug concentrations were assayed in various specimens. Peak plasma concentration (Cmax)-to-minimum inhibitory concentration (MIC; Cmax-to-MIC) ratios and the area under the concentration versus time curve over a 12-hour period-to-MIC ratios (AUC(12h)-to-MIC) were calculat-ed. RESULTS: Danofloxacin and enrofloxacin had MICs of 0.03 microg/mL for the M. haemolytica challenge isolate. Danofloxacin administered at doses of 6 and 8 mg/kg resulted in numerically higher geometric mean concentrations of danofloxacin in plasma and all respiratory tissues than geometric mean concentrations of enrofloxacin after treatment with enrofloxacin. Geometric mean concentrations of enrofloxacin were numerically higher than geometric mean concentrations of ciprofloxacin metabolite in plasma and almost all respiratory tissues. Danofloxacin and enrofloxacin achieved Cmax-to-MIC ratios >10 and AUC(12h)-to-MIC ratios >125 hours. CONCLUSIONS AND CLINICAL RELEVANCE: When used to treat pneumonic pasteurellosis in calves, danofloxacin and enrofloxacin can be expected to deliver concentration-dependent bactericidal activity against M. haemolytica, the bacteria most commonly associated with bovine respiratory tract disease.     

Health and performance of young dairy calves vaccinated with a modified-live Mannheimia haemolytica and Pasteurella multocida vaccine.

OBJECTIVE: To evaluate the health and performance of young dairy calves vaccinated with a commercial Mannheimia haemolytica and Pasteurella multocida vaccine. DESIGN: Randomized clinical trial. ANIMALS: 358 Holstein dairy calves between 14 and 20 days of age on 8 farms. PROCEDURE: Calves were randomly assigned to a control or vaccinated group. The vaccine used was a commercial modified-live M. haemolytica and P. multocida vaccine that was administered on days 0 and 14. Calf weight was measured on day 0 and monthly for 3 months. Farmers were asked to record any treatment given to the calves and the reason for treatment during the 4 months of the study. Blood was collected from all calves on days 0 and 28, and titers of antibodies to M. haemolytica were determined by means of direct bacterial agglutination. RESULTS: Mean daily gain was not significantly different between vaccinated and control calves. Vaccinated calves had a significantly greater increase in antibody titers (5.3-fold increase), compared with control calves (3.6-fold increase). There was no significant difference between vaccinated and control calves for any of the treatment outcomes (number and duration of treatments and age at first and last treatments). CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the M. haemolytica and P. multocida vaccine, given twice 2 weeks apart, was effective in increasing titers of antibodies against M. haemolytica in young dairy calves but did not improve calf performance or health.     

Effect of intranasal exposure to leukotoxin-deficient Mannheimia haemolytica at the time of arrival at the feedyard on subsequent isolation of M haemolytica from nasal secretions of calves

OBJECTIVE: To determine the effect of intranasal exposure to live leukotoxin (LktA)-deficient Mannheimia haemolytica (MH) at the time of feedyard arrival on nasopharyngeal colonization by wild-type MH in calves. ANIMALS: 200 calves. PROCEDURE: Calves from Arkansas (AR calves; n = 100; mean body weight, 205 kg) were purchased from an order buyer barn. Calves from New Mexico (NM calves; n = 100; mean body weight, 188 kg) were obtained from a single ranch. Calves were transported to a feedyard, where half of each group was exposed intranasally with LktA-deficient MH at the time of arrival. Calves were observed daily for respiratory tract disease (RTD), and nasal swab specimens were collected periodically to determine nasopharyngeal colonization status with MH. Serum samples were assayed for antibodies to MH. RESULTS: 15 AR calves had nasopharyngeal colonization by wild-type MH at the order buyer barn, whereas none of the NM calves had nasopharyngeal colonization. Intranasal exposure to LktA-deficient MH elicited an increase in serum antibody titers against MH in NM calves, but titers were less in NM calves treated for RTD. Exposure of NM calves to LktA-deficient MH offered protection from nasopharyngeal colonization by wild-type MH. CONCLUSIONS AND CLINICAL RELEVANCE: Exposure of calves to LktA-deficient MH elicited an increase in serum antibody titers against MH and decreased colonization of the nasopharynx by wild-type MH. Earlier exposure would likely allow an immune response to develop before transportation and offer protection from nasopharyngeal colonization and pneumonia caused by wild-type MH.     

Maternally and naturally acquired antibodies to Mannheimia haemolytica and Pasteurella multocida in beef calves

The dynamics and duration of maternally derived antibodies as well as the onset of acquired immunity against Mannheimia haemolytica and Pasteurella multocida in range-pastured beef calves were investigated. Two groups of unvaccinated cattle were used in this study. Serum antibody responses were measured by enzyme-linked immunoassay for antibodies of the IgG1, IgG2 and IgM isotypes binding M. haemolytica whole cells (WC) or leukotoxin (LKT) and P. multocida outer membrane proteins (OMPs). Comparisons of mean antibody responses to M. haemolytica LKT and WC and P. multocida OMPs were made within each group. Maternally derived antibodies against M. haemolytica and P. multocida reached lowest levels at 30-90 days after birth. Calves began production of antibodies against M. haemolytica and P. multocida between 60 and 90 days of age in both groups. Based on the results of this study, in beef herds vaccinated against M. haemolytica and/or P. multocida, it may be best to vaccinate calves around 3 months of age. In contrast, beef calves from unvaccinated herds might benefit from vaccination at 4 months of age.     

Role of platelet-activating factor in alveolar septal injury associated with experimentally induced pneumonic pasteurellosis in calves

OBJECTIVE: To determine whether platelet-activating factor (PAF) is involved in acute lung microvascular injury associated with pneumonic pasteurellosis in calves. ANIMALS: 15 healthy 2- to 4-week-old male Holstein calves. PROCEDURE: Calves were anesthetized and inoculated intrabronchially with saline (0.9% NaCl) solution (n = 5) or 1x10(9) Pasteurella haemolytica organisms (n = 10). Of the 10 calves inoculated with P haemolytica, 5 also were treated with WEB 2086, a potent inhibitor of PAF, and 5 were treated with vehicle. Blood and bronchoalveolar lavage samples were collected before and 1, 2, 4, and 6 hours after inoculation of P. haemolytica. Blood samples were analyzed to evaluate total number and differential counts of leukocytes, dilute whole-blood leukocyte deformability, size of neutrophils, and neutrophil CD11b expression. Bronchoalveolar lavage samples were analyzed for total number and differential counts of nucleated cells, total protein concentration, and hemoglobin concentration. Size and gross and histologic appearance of lung lesions also was determined. RESULTS: Treatment of calves with WEB 2086 reduced size of lung lesions, attenuated the increase in microvascular permeability, and reduced neutrophil infiltration in the first 4 hours after inoculation. Treatment with WEB 2086 also attenuated a decrease in leukocyte deformability, increase in size of neutrophils, and CD11b expression by circulating neutrophils. CONCLUSIONS AND CLINICAL RELEVANCE: It appears that PAF is a major mediator for altered lung microvascular permeability and activation of circulating neutrophils in the first 4 hours after onset of pneumonic pasteurellosis in calves.     

In vitro evaluation of the role of platelet-activating factor and interleukin-8 in Mannheimia haemolytica-induced bovine pulmonary endothelial cell injury

OBJECTIVE: To develop an in vitro model of the bovine alveolar-capillary interface and to evaluate the roles of interleukin-8 (IL-8) and platelet-activating factor (PAF) in neutrophil-mediated endothelial injury induced by infection with Mannheimia haemolytica. SAMPLE POPULATION: Cultured bovine pulmonary microvascular endothelial cells, freshly isolated bovine neutrophils, and monocyte-derived bovine macrophages. PROCEDURE: A coculture system was developed in which endothelial cells were grown to confluence in tissue culture inserts, neutrophils were added to the inserts, and macrophages were added to tissue culture wells. Mannheimia haemolytica-derived lipopolysaccharide (LPS) or supernatant was added to activate macrophages, and inhibitors of PAF or IL-8 were added to the insert. Endothelial cell cytotoxicity and permeability (ie, albumin leakage) and neutrophil activation (ie, adhesion, degranulation [lactoferrin expression], and superoxide production) were assessed. RESULTS: The addition of M haemolytica-derived LPS to bovine macrophages in the coculture system resulted in significant increases in endothelial cell cytotoxicity and permeability and neutrophil degranulation and adhesion. Inhibition of IL-8 reduced endothelial cell permeability and neutrophil degranulation induced by exposure to M haemolytica-derived supernatant, whereas inhibition of PAF decreased superoxide release by neutrophils. CONCLUSIONS AND CLINICAL RELEVANCE: In vitro activation of bovine macrophages by M haemolytica-derived LPS resulted in neutrophil activation and neutrophil-mediated endothelial damage. Neutrophil-mediated endothelial injury and neutrophil degranulation were, at least in part, mediated by IL8, whereas PAF promoted superoxide release by neutrophils in this in vitro system designed to mimic the in vivo events that occur during the early stages of bovine pneumonic pasteurellosis.     

Effect of danofloxacin and tilmicosin on body temperatures of beef calves with pneumonia experimentally induced by inoculation with Mannheimia haemolytica

OBJECTIVE: To examine effects of danofloxacin and tilmicosin on continuously recorded body temperature in beef calves with pneumonia experimentally induced by inoculation of Mannheimia haemolytica. ANIMALS: 41 Angus-cross heifers (body weight, 160 to 220 kg) without a recent history of respiratory tract disease or antimicrobial treatment, all from a single ranch. PROCEDURE: Radiotransmitters were implanted intravaginally in each calf. Pneumonia was induced intrabronchially by use of logarithmic-phase cultures of M. haemolytica. At 21 hours after inoculation, calves were treated with saline (0.9% NaCl) solution, danofloxacin, or tilmicosin. Body temperature was monitored from 66 hours before inoculation until 72 hours after treatment. Area under the curve (AUC) of the temperature-time plot and mean temperature were calculated for 3-hour intervals and compared among treatment groups. RESULTS: The AUCs for 3-hour intervals did not differ significantly among treatment groups for any of the time periods. Analysis of the mean temperature for 3-hour intervals revealed significantly higher temperatures at most time periods for saline-treated calves, compared with temperatures for antimicrobial-treated calves; however, we did not detect significant differences between the danofloxacin- and tilmicosin-treated calves. The circadian rhythm of temperatures before exposure was detected again approximately 48 hours after bacterial inoculation. CONCLUSIONS AND CLINICAL RELEVANCE: Danofloxacin and tilmicosin did not differ in their effect on mean body temperature for 3-hour intervals but significantly decreased body temperature, compared with body temperature in saline-treated calves. Normal daily variation in body temperature must be considered in the face of respiratory tract disease during clinical evaluation of feedlot cattle.     

Efficacy of ivermectin against the abomasal nematode mecistocirrus digitatus in naturally infected zebu calves

Anthelmintic efficacy of ivermectin against Mecistocirrus digitatus was evaluated in 10 naturally infected zebu calves. Group 1 (n = 5) was not treated, and group 2 (n = 5) was treated SC with 200 micrograms of ivermectin/kg of body weight. Calves were euthanatized 14 or 15 days after treatment. There was 100% overall reduction of M digitatus in treated calves, which was significant (P = 0.0079) compared with reduction in controls. Cooperia punctata, Haemonchus similis, and Trichostrongylus axei were found in controls. Efficacy against these parasites in treated calves was 100%.     

Comparison of pathophysiologic changes in the lungs of calves challenge exposed with Escherichia coli-derived endotoxin and Pasteurella haemolytica, alone or in combination

Pulmonary responses to intratracheal challenge exposure with Pasteurella haemolytica, with or without Escherichia coli-derived endotoxin, E coli endotoxin alone, or saline solution were compared in anesthetized, mechanically ventilated neonatal calves. Baseline values for dynamic compliance, total pulmonary resistance, functional residual capacity, arterial blood gas tensions, hemogram, leukogram, and systemic and pulmonary arterial pressures were recorded for each calf. After baseline data were obtained, calves were challenge exposed with logarithmic-growth phase P haemolytica organisms with or without E coli endotoxin, E coli endotoxin alone, or saline solution (0.9% NaCl). Physiologic data were obtained immediately after challenge exposure and at various intervals over the next 6 hours. Calves challenge exposed with P haemolytica alone developed sever hypoxemia, had increased alveolar-arterial oxygen difference and threefold increases in total pulmonary resistance, became hypercarbic, had decreased functional residual capacity, and developed systemic hypotension without change in pulmonary arterial pressure. At necropsy, these calves had extensive multifocal areas of necrohemorrhagic and purulent pneumonia. Ratio of extravascular lung water to lung dry weight was not significantly increased in lung specimens obtained from calves challenge exposed with P haemolytica, but ratio of lung wet weight to dry weight was increased, indicating that increased lung wet weight was attributable largely to increased solids and not to fluid alone. (Extravascular lung water measurement excludes fluid from the vascular compartment.) Intratracheal challenge exposure with endotoxin failed to alter lung function and caused minor changes in lung structure consisting of focal areas of hemorrhage and edema.(ABSTRACT TRUNCATED AT 250 WORDS)     

Serum antibodies to Pasteurella haemolytica lipopolysaccharide: relationship to experimental bovine pneumonic pasteurellosis

An enzyme-linked immunosorbent assay was used to determine the serum antibody response to Pasteurella haemolytica lipopolysaccharide (LPS) for calves vaccinated with saline solution, a formalin-killed P haemolytica bacterin, or live P haemolytica. Bacterin-vaccinated calves had a lower antibody response to LPS than did calves vaccinated with live P haemolytica. Calves vaccinated with either saline solution or the bacterin were more susceptible to intrapulmonic challenge exposure with P haemolytica than were calves vaccinated with liver organisms. Serum antibody responses to P haemolytica LPS did not seem important for resistance to challenge exposure, because there was no significant correlation (P greater than 0.05) between the lung lesion score and antibody response to P haemolytica LPS. There was a highly significant correlation (P less than 0.001) between antibody detected against P haemolytica LPS and that against formalin-killed P haemolytica. Competitive binding studies indicated that P haemolytica LPS is a major antigenic determinant on the surface of P haemolytica. There did not seem to be substantial cross-reaction between LPS from P haemolytica and that from Escherichia coli (serotype O26:B6).