Comparison of protection of experimentally challenged cattle vaccinated once or twice with a Pasteurella haemolytica bacterial extract vaccine.

Three groups of calves (15-18 per group) were injected twice at a 3-week interval with 2 doses of phosphate buffered saline (PBS, CONTROL group), 2 doses of PRESPONSE, a Pasteurella haemolytica A1 bacterial extract vaccine (PRESPONSE-2 group) or 1 dose of PBS followed by a 2nd vaccination with 1 dose of PRESPONSE (PRESPONSE-1 group). Three weeks after the 2nd vaccination, the calves were challenged intratracheally with P. haemolytica A1. Calves were evaluated clinically for 3 days prior to challenge and for 5 days after challenge. Six days postchallenge, calves were either euthanized or sent to slaughter and the lungs were evaluated for percent pneumonic tissue. There was a significant effect of single or double application of vaccine on clinical scores (P = 0.0409). Percent pneumonic tissue at necropsy was significantly affected by vaccine group (P = 0.014). Calves in the CONTROL group had significantly higher percent pneumonic tissue after arcsine transformation (45.30%) than calves in any group receiving PRESPONSE, regardless of vaccination frequency (25.18% and 25.78%, for calves receiving 2 doses or 1 dose of PRESPONSE, respectively). Both serum toxin neutralizing and direct agglutinating titers were negatively correlated with percent pneumonic tissue. Most importantly, 1 dose of PRESPONSE was as efficient as 2 doses at eliciting a protective immune response. It is concluded that the presence of P. haemolytica as a natural commensal in the upper respiratory tract of the calf can effectively prime the animal, and allow the animal to respond in an anamnestic nature to only 1 dose of this vaccine.     

Vaccination studies against experimental bovine Pasteurella pneumonia.

Vaccination-challenge experiments were conducted in colostrum-deprived calves to evaluate the efficacy of Pasteurella bacterins and vaccines against experimental pneumonic pasteurellosis. Calves were vaccinated with formalin-killed bacterins and live vaccines, then challenge exposed intratracheally with P. haemolytica or P. multocida. Infectious bovine rhinotracheitis virus was inoculated intranasally three to four days prior to P. haemolytica challenge-exposure. All calves were examined for macroscopic and microscopic lesions after being found dead or following euthanasia four to seven days after challenge exposure with the bacterial pathogen. Clinical, hematological, and pathological responses to challenge exposure in aluminum hydroxide absorbed P. haemolytica and P. multocida bacterin-treated calves were consistent with the pneumonic lesions of pulmonary pasteurellosis in the control calves. An oil-adjuvanted P. haemolytica bacterin limited clinical and pathological responses in the affected calves whereas a P. multocida oil-adjuvanted bacterin did not. Both clinical and pathological responses to challenge exposure in calves vaccinated with live Pasteurella vaccines were less severe than those of the control calves. Vaccine effectiveness appeared to be dose dependent.     

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.     

Proliferation of Pasteurella haemolytica in the calf respiratory tract after an abrupt change in climate

Two groups of four calves were exposed to a poly-disperse aerosol of 1.3 X 10(4) to 16 X 10(4) colony forming units (CFU) of nalidixic acid resistant Pasteurella haemolytica type A1 litre-1 of air with a mass median aerodynamic diameter of 2.6 +/- 0.8 microns. One group of calves was kept at 5 degrees C, 72 per cent relative humidity (RH) and the second was subjected to an abrupt change in climate directly after aerosol exposure from 5 degrees C, 75 per cent RH to 13 degrees C, 84 per cent RH. Clearance of the organism from the respiratory tract of the calves was monitored over the subsequent 23 hours by a method of tracheal and nasopharyngeal swabbing. Clearance measured at the trachea in all calves in both groups was not a continuous, uninterrupted process but exhibited a temporary decline between eight and 14 hours. Calves subjected to an abrupt change in climate after aerosol challenge had raised respiratory rates eight to 14 hours later and P haemolytica proliferated in the nasopharynx over the entire 23 hours. There was no apparent effect of climate on P haemolytica in the trachea. It is suggested that rapid growth of P haemolytica accompanying a change in climate may be an important aetiological factor in pneumonic pasteurellosis of calves.     

Effects of experimentally induced Pasteurella haemolytica pneumonia on the pharmacokinetics of erythromycin in the calf

Pneumonic pasteurellosis was produced experimentally in 3- to 4-month-old Holstein bull calves by bilateral intrapulmonary administration of 5 X 10(7) to 10(9) colony-forming units of Pasteurella haemolytica. Of 8 calves, 4 developed minor pulmonary changes, 1 died of an apparent bacteremia within 24 hours, and 3 developed extensive pneumonic changes. At 1 week before (1 dose) and at 48, 60, and 72 hours (3 doses) after Pasteurella administration, the calves were given erythromycin at a dosage of 15 mg/kg, and the pharmacokinetic values were determined. There were statistically (P less than or equal to 0.05) significant increases in the distribution and elimination rates associated with pneumonia. The elimination half life decreased from 132.7 +/- 9.6 minutes in prepneumonic calves to 111.1 +/- 13.8 minutes and 99.7 +/- 2.6 minutes in calves with minor and with moderate pneumonic changes, respectively. There also was a decrease in apparent volume of distribution with pneumonia. Erythromycin tissue concentrations were determined 2 hours after the last dose was given to the calves with pneumonia. Tissue concentrations in the pneumonic lung areas were as high or higher than those in nonaffected lung tissues in the same animals. Because of the increased rate of elimination from serum in pneumonic calves, it may be advisable to use shorter dosage intervals in calves with severe respiratory tract disease.     

Induction of immunity against pneumonic pasteurellosis following experimental infection in calves.

Immunity against pneumonic pasteurellosis was studied in calves after recovery from experimental respiratory disease with Pasteurella haemolytica. Nine calves were exposed to aerosols of parainfluenza-3 virus and Pasteurella haemolytica A1 six days apart to produce respiratory disease. After recovery from the disease, these nine principal and four control calves were challenged with aerosols of bovine herpesvirus 1 and P. haemolytica A1 four days apart. With this viral-bacterial challenge, the nine principal animals failed to develop clinical responses to this bacterial challenge and their lungs did not show the growth of P. haemolytica on cultures, whereas two of four control calves had elevated temperatures and developed necropurulent pneumonia with the isolation of P. haemolytica from the lungs. The principal calves had developed high levels of cytotoxin neutralizing antibodies in their sera following parainfluenza-3 virus-P. haemolytica infection. This demonstrated that immunity against pneumonic pasteurellosis can be achieved, with a suggestion that further search for an effective vaccine for P. haemolytica is warranted.     

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.     

Experimental induction of pneumonic pasteurellosis in calves by intratracheal infection with Pasteurella multocida biotype A:3

The study aimed to establish an experimental model to investigate the pathogenesis of lung infection by Pasteurella multocida, an important cause of bovine respiratory disease. An experimental model is required to assist the development of an effective vaccine. Sixteen 8-week-old calves were challenged intratracheally with 10(9) or 10(10) colony forming units of P. multocida in either 60 or 300 ml saline in a 2 x 2 factorial experiment. All animals became dull within 2-6h post-infection (p.i.) and two calves were killed humanely because of suspected endotoxic shock. Remaining animals showed increased respiratory rates by 15-20 h p.i. and, at 23 h p.i., calves given the high dose, high volume challenge showed higher (P < 0.05) rectal temperatures. From 24 to 36 h p.i., clinical signs decreased in a majority of animals. Plasma haptoglobin concentrations increased (P < 0.05) in calves given the high volume challenge irrespective of the number of bacteria. At post-mortem examination (4d p.i.), lung lesions, mainly in the apical lobes, were found in all calves. Histopathological examination showed areas of purulent pneumonia with a tendency to abscessation and inflamed interlobular septa characterised by accumulation of neutrophils and oedema. The clinical and pathological responses described were typical of bovine pneumonic pasteurellosis.     

Effects of intravenous Escherichia coli dose on the pathophysiological response of colostrum-fed Jersey calves

Objectives of the present study were to characterize the dose dependency of an intravenous Escherichia coli O111:H8 challenge in colostrum-fed Jersey calves and to identify any biochemical markers indicative of septicemia. Eighteen 3-week old colostrum-fed Jersey calves were completely randomized to 1 of 6 doses of E. coli O111:H8. The challenge doses included 0, 1.5 x 10?, 1.5 x 10?, 1.5 x 10?, 1.5 x 10?, and 1.5 x 10? colony-forming units (CFU) given intravenously as a bolus in 5 mL of sterile isotonic saline. Peripheral blood samples were collected at 0, 2, 4, 8, 12, 24, and 48 h relative to the challenge for biochemical, total leukocyte count, and differential analyses. Rectal temperatures were collected via indwelling rectal temperature probes at 5-min intervals, and hourly averages calculated from 2 d prior to the challenge till 2 d after the challenge. All calves survived the 48 h observation period following the challenge. Calves given 1.5 x 10? and 1.5 x 10? CFU displayed sickness behaviors (P < 0.01) beginning 0.5 h after the challenge and returned to that of the control calves by 6 and 32 h for calves challenged with 1.5 x 10? and 1.5 x 10? CFU, respectively. There were treatment x time interactions (P < 0.01) on total leukocyte counts and plasma glucose and zinc concentrations. Calves administered 1.5 x 10? and 1.5 x 10? CFU had leucopenia beginning 2 h after the challenge and returning to counts similar to the control calves within 24 h. Additionally, those calves were hypoglycemic from 4 to 12h after the challenge with the degree of hypoglycemia inversely related to the dose of the E. coli. All calves challenged with E. coli had decreased plasma zinc concentrations, and the magnitude was inversely proportional to the challenge dose. There were treatment x time interactions (P < 0.001) on rectal temperatures following the challenge. All calves challenged with E. coli developed a febrile response, but the intensity and duration of the response were dependent on the challenge dose. These data indicate that calves intravenously challenged with 1.5 x 10? and 1.5 x 10? CFU of the E. coli O111:H8 showed immediate clinical and biochemical signs indicative of septicemia. However, calves administered 1.5 x 10? or less of the E. coli had febrile responses, but did not develop septicemia. Blood glucose and zinc concentrations may be dose responsive indicators that could potentially differentiate between a septicemic versus non-septicemic calf.     

Longevity of protective immunity to experimental bovine herpesvirus-1 infection following inoculation with a combination modified-live virus vaccine in beef calves

OBJECTIVE: To determine whether a combination viral vaccine containing modified-live bovine herpesvirus-1 (BHV-1) would protect calves from infection with a recent field isolate of BHV-1. DESIGN: Randomized controlled trial. ANIMALS: Sixty 4- to 6-month-old beef calves. PROCEDURE: Calves were inoculated with a placebo 42 and 20 days prior to challenge (group 1; n = 10) or with the combination vaccine 42 and 20 days prior to challenge (group 2; 10), 146 and 126 days prior to challenge (group 3; 10), 117 and 96 days prior to challenge (group 4; 10), 86 and 65 days prior to challenge (group 5; 10), or 126 days prior to challenge (group 6; 10). All calves were challenged with BHV-1 via aerosol. Clinical signs, immune responses, and nasal shedding of virus were monitored for 14 days after challenge. RESULTS: Vaccination elicited increases in BHV-1-specific IgG antibody titers. Challenge with BHV-1 resulted in mild respiratory tract disease in all groups, but vaccinated calves had less severe signs of clinical disease. Extent and duration of nasal BHV-1 shedding following challenge was significantly lower in vaccinated calves than in control calves. In calves that received 2 doses of the vaccine, the degree of protection varied with the interval between the last vaccination and challenge, as evidenced by increases in risk of clinical signs and extent and duration of viral shedding. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that this combination vaccine provided protection from infection with virulent BHV-1 and significantly reduced nasal shedding of the virus for at least 126 days after vaccination.     

Association between changes in eating and drinking behaviors and respiratory tract disease in newly arrived calves at a feedlot

OBJECTIVE: To investigate eating and drinking behaviors and their association with bovine respiratory disease complex (BRDC) and to evaluate methods of diagnosing BRDC. ANIMALS: 170 newly arrived calves at a feedlot. PROCEDURE: Eating and drinking behaviors of calves were recorded at a feedlot. Calves with clinical signs of BRDC were removed from their pen and classified retrospectively as sick or not sick on the basis of results of physical and hematologic examinations. Pulmonary lesions of all calves were assessed at slaughter. RESULTS: Calves that were sick had significantly greater frequency and duration of drinking 4 to 5 days after arrival than calves that were not sick. Sick calves had significantly lower frequency and duration of eating and drinking 11 to 27 days after arrival but had significantly greater frequency of eating 28 to 57 days after arrival than calves that were not sick. Calves at slaughter that had a higher percentage of lung tissue with pneumonic lesions had significantly lower frequency and duration of eating 11 to 27 days after arrival but had significantly higher frequency and duration of eating 28 to 57 days after arrival. Agreement for calves being sick and having severe pulmonary lesions at slaughter was adequate. Agreement for calves being removed and having pulmonary lesions at slaughter was low. CONCLUSIONS AND CLINICAL RELEVANCE: Eating and drinking behaviors were associated with signs of BRDC, but there was not an obvious predictive association between signs of BRDC in calves and eating and drinking behaviors. Fair to poor agreement was observed between antemortem and postmortem disease classification.     

Experimental production of bovine pneumonic pasteurellosis

Pneumonic pasteurellosis has been reproduced in conventional, weaned, Friesian-cross calves using a strain of Pasteurella haemolytica biotype A, serotype 1 (P haemolytica A1) isolated from a pathologically confirmed incident of bovine pneumonic pasteurellosis. The major clinical findings were pyrexia, hyperpnoea, tachypnoea, nasal discharge and reduced appetite. Fibrinous pneumonia was present in the lungs of animals at necropsy on days 2 and 3 after initial infection while by days 9 and 10 after initial infection many of the areas of fibrinous pneumonia were confined by a fibrous capsule forming well defined nodules. During the experiment natural transmission of the infecting strain of P haemolytica A1 occurred in two control calves which developed a condition identical to that in the artificially infected calves. P haemolytica A1 was repeatedly recovered from the nasopharynx of infected calves and at necropsy throughout the upper and lower respiratory tracts. Seroconversion, as measured by indirect haemagglutination, to the organism developed in all infected calves by days 9 and 10 after initial infection. The clinical, microbiological and pathological findings were identical to those seen in field incidents of bovine pneumonic pasteurellosis involving recently housed, weaned, single-suckled calves.     

Characterization of a Pasteurella multocida (serotype B) bovine pneumonic pasteurellosis model and the effect of antimicrobials during peracute infection

A method to produce bovine pneumonic pasteurellosis for experimental purposes was studied and the clinical response of experimentally infected calves to selected antimicrobials was characterized. Male Holstein calves stressed with multiple hot and cold water applications followed by intratracheal inoculation of broth cultures of Pasteurella multocida serotype B developed acute clinical illness consistent with pneumonia. Infected, untreated calves consistently developed classic pneumonic pasteurellosis, infected calves treated with either oxytetracycline or sulfadimethoxine recovered from acute clinical disease, and the uninfected controls remained healthy. This disease model offers potential for use in pharmacokinetic and target tissue drug concentration studies and for dosage titration of drugs intended for treatment of bacterial pneumonias.     

Evidence that blood-borne infection is involved in the pathogenesis of bovine pneumonic pasteurellosis

Five calves were inoculated intravenously with 10(8) colony forming units (cfu) of Pasteurella haemolytica A1; the mean score for pneumonic consolidation 3 days post-inoculation was 28%, and the mean clinical score was 7.8. Five calves inoculated intratracheally with 10(9) cfu of the same strain of P. haemolytica had comparable scores (34% and 8.8). Histological lesions of fibrinous pneumonia were similar in all calves. P. haemolytica was recovered from all but one of the affected lungs. From one calf killed in extremis 3 hours after intravenous inoculation, numbers of bacteria recovered from lung were 1,000-fold greater than from liver and spleen. A similar difference in bacterial numbers was also obtained from a gnotobiotic calf killed in extremis, 12 hours after intravenous inoculation of 10(8) cfu P. haemolytica. Evidence from these experiments supports the hypothesis that the blood-borne route is important in the pathogenesis of bovine pneumonic pasteurellosis.     

Characterization of protection from systemic infection and disease by use of a modified-live noncytopathic bovine viral diarrhea virus type 1 vaccine in experimentally infected calves

OBJECTIVE: To evaluate protection against systemic infection and clinical disease provided by use of a modified-live noncytopathic bovine viral diarrhea virus (BVDV) type 1 vaccine in calves challenged with NY-1 BVDV. ANIMALS: 10 calves, 5 to 7 months of age. PROCEDURES: Calves were allocated (n = 5/group) to be nonvaccinated or vaccinated SC on day 0 with BVDV type 1 (WRL strain). Calves in both groups were challenged intranasally with NY-1 BVDV on day 21. Calves' rectal temperatures and clinical signs of disease were recorded daily, total and differential WBC and platelet counts were performed, and serum neutralizing antibody titers against NY-1 BVDV were determined. Histologic examinations and immunohistochemical analyses to detect gross lesions and distribution of viral antigens, respectively, were performed. RESULTS: After challenge exposure to NY-1 BVDV, nonvaccinated calves developed high rectal temperatures, increased respiratory rates, viremia, leukopenia, lymphopenia, and infection of the thymus. Vaccinated calves did not develop high rectal temperatures or clinical signs of respiratory tract disease. Vaccinated calves appeared to be protected against systemic replication of virus in that they did not develop leukopenia, lymphopenia, viremia, or infection of target organs, and infectious virus was not detected in peripheral blood mononuclear cells or the thymus. CONCLUSIONS AND CLINICAL RELEVANCE: The modified-live BVDV vaccine protected calves against systemic infection and disease after experimental challenge exposure with NY-1 BVDV. The vaccine protected calves against infection and viremia and prevented infection of target lymphoid cells.     

Evaluation of age-dependent susceptibility in calves infected with two doses of Mycobacterium avium subspecies paratuberculosis using pathology and tissue culture

The longstanding assumption that calves of more than 6 months of age are more resistant to Mycobacterium avium subspecies paratuberculosis (MAP) infection has recently been challenged. In order to elucidate this, a challenge experiment was performed to evaluate age- and dose-dependent susceptibility to MAP infection in dairy calves. Fifty-six calves from MAP-negative dams were randomly allocated to 10 MAP challenge groups (5 animals per group) and a negative control group (6 calves). Calves were inoculated orally on 2 consecutive days at 5 ages: 2 weeks and 3, 6, 9 or 12 months. Within each age group 5 calves received either a high – or low – dose of 5 × 10⁹ CFU or 5 × 10⁷ CFU, respectively. All calves were euthanized at 17 months of age. Macroscopic and histological lesions were assessed and bacterial culture was done on numerous tissue samples. Within all 5 age groups, calves were successfully infected with either dose of MAP. Calves inoculated at < 6 months usually had more culture-positive tissue locations and higher histological lesion scores. Furthermore, those infected with a high dose had more severe scores for histologic and macroscopic lesions as well as more culture-positive tissue locations compared to calves infected with a low dose. In conclusion, calves to 1 year of age were susceptible to MAP infection and a high infection dose produced more severe lesions than a low dose.     

Response of calves to challenge exposure with virulent bovine respiratory syncytial virus following intranasal administration of vaccines formulated for parenteral administration

OBJECTIVE: To determine whether single-fraction and combination modified-live bovine respiratory syncytial virus (BRSV) vaccines commercially licensed for parenteral administration could stimulate protective immunity in calves after intranasal administration. DESIGN: Randomized controlled trial. ANIMALS: 39 calves. PROCEDURES: Calves were separated from dams at birth, fed colostrum with a minimal concentration of antibodies against BRSV, and maintained in isolation. In 2 preliminary experiments, 9-week-old calves received 1 (n = 3) or 2 (3) doses of a single-component, modified-live BRSV vaccine or no vaccine (8 control calves in each experiment), and were challenged with BRSV 21 days after vaccination. In a third experiment, 2-week-old calves received combination modified-live virus (MLV) vaccines with or without BRSV and calves were challenged with BRSV 8 days later. Calves were euthanized, and lung lesions were measured. Immune responses, including serum and nasal antibody and nasal interferon-alpha concentrations, were assessed. RESULTS: BRSV challenge induced signs of severe clinical respiratory tract disease, including death and pulmonary lesions in unvaccinated calves and in calves that received a combination viral vaccine without BRSV. Pulmonary lesions were significantly less severe in BRSV-challenged calves that received single or combination BRSV vaccines. The proportion of calves that shed virus and the peak virus titer was decreased, compared with control calves. Protection was associated with mucosal IgA antibody responses after challenge. CONCLUSIONS AND CLINICAL RELEVANCE: Single and combination BRSV vaccines administered intranasally provided clinical protection and sparing of pulmonary tissue similar to that detected in response to parenteral delivery of combination MLV and inactivated BRSV vaccines previously assessed in the same challenge model.     

Characterization of protection against systemic infection and disease from experimental bovine viral diarrhea virus type 2 infection by use of a modified-live noncytopathic type 1 vaccine in calves

OBJECTIVE: To evaluate protection resulting from use of a modified-live noncytopathic bovine viral diarrhea virus (BVDV) type 1 vaccine against systemic infection and clinical disease in calves challenged with type 2 BVDV. ANIMALS: 10 calves, 5 to 7 months of age. PROCEDURES: Calves were allocated (n = 5/group) to be nonvaccinated or vaccinated SC on day 0 with BVDV 1 (WRL strain). Calves in both groups were challenged intranasally with BVDV type 2 isolate 890 on day 21. Rectal temperatures and clinical signs of disease were recorded daily, and total and differential WBC and platelet counts were performed. Histologic examinations and immunohistochemical analyses to detect lesions and distribution of viral antigens, respectively, were performed. RESULTS: After challenge exposure to BVDV type 2, nonvaccinated calves developed high rectal temperatures, increased respiratory rates, viremia, leukopenia, lymphopenia, and infection of the thymus. Vaccinated calves did not develop high rectal temperatures or clinical signs of respiratory tract disease. Vaccinated calves appeared to be protected against systemic replication of virus in that they did not develop leukopenia, lymphopenia, viremia, or infection of target organs, and infectious virus was not detected in peripheral blood mononuclear cells or the thymus. CONCLUSIONS AND CLINICAL RELEVANCE: The modified-live BVDV type 1 vaccine protected against systemic infection and disease after experimental challenge exposure with BVDV type 2. The vaccine protected calves against infection and viremia and prevented infection of target lymphoid cells.     

Experimental bovine respiratory tract disease with Haemophilus somnus

Eight calves were inoculated into the bronchus with H. somnus. Thirteen calves were inoculated with bovine respiratory syncytial virus (BRSV) and 8 days later with H. somnus. All calves developed necrotizing, suppurative, lobular bronchopneumonia and pleuritis. Clinical signs of disease and pneumonic lesions were significantly more severe in calves that were sequentially inoculated with BRSV followed by H. somnus. Pneumonic lesions in the inoculated calves were similar to those described for naturally occurring H. somnus-associated respiratory tract disease. Control calves inoculated with BRSV alone or sham-inoculated with medium did not develop clinical signs of respiratory tract disease. The BRSV-inoculated control calves developed minimal pneumonic lesions.     

Volume-controlled bronchopulmonary lavage of normal and pneumonic calves

Saline bronchopulmonary lavage of the right lung of 16 anesthetized calves was performed using a single-lumen cuffed endotracheal tube. The initial volume of saline introduced was based on the functional residual capacity (FRC) of the right lung lobes as determined from the proportional weights of the right (58% of total FRC) and left (42% of total FRC) lung lobes. Calves were divided into "pneumonic" and "normal" groups based on clinical signs. Five sequential washes were done on each calf. There was no difference in the percentage of total lavage fluid volume recoverable between normal (83.8 +/- 4.2%) and pneumonic (81.1 +/- 8.2%) calves. Cell yield in the initial wash was consistently greater than in subsequent washes for both normal (12.7 +/- 6.6 X 10(6) cells/kg body weight) and pneumonic (58.1 +/- 37.6 X 10(6) cells/kg body weight) calves, and constituted 62.0% (normal) and 75.4% (pneumonic) of the total recoverable cell yield. Total cell yields were higher (P less than 0.05) in pneumonic calves, primarily due to neutrophil leukocytes (PMN). Neutrophils constituted 53.7 +/- 25% of the total cell yield in the pneumonic calves, but only 12.3 +/- 9.5% in the normal calves. The pulmonary alveolar macrophage (PAM) was the major recoverable cell in normal calves (85.7 +/- 8.7% of total lavage cells). Macrophages constituted a smaller (42.9 +/- 23.5) percentage of the total lavage cells in the pneumonic group due to increased PMN numbers. Viability of recovered cells from the pneumonic calves (91.5 +/- 4.8%) was lower than for the normal calves (94.1 +/- 2.5%), but the difference was not significant.(ABSTRACT TRUNCATED AT 250 WORDS)