Objective—To develop and validate an ex vivo model
for study of adherence of Mannheimia haemolytica
(formerly Pasteurella haemolytica) to respiratory tract
mucosa of cattle and to use this model to confirm
adherence of M haemolytica serovar 1 (Mh1) to several
relevant respiratory mucosal surfaces.
Sample Population—Excised nasal, nasopharyngeal,
turbinate, and tonsillar mucosal tissue from the
bovine upper respiratory tract.
Procedure—Mh1 was radiolabeled by use of tritiated
leucine. Various concentrations of labeled bacteria
were incubated with bovine upper respiratory tract
tissues for various times. Tissue was washed to
remove nonadherent bacteria, and percentage of bacteria
adhered (percentage of adherence) was estimated
using radioactivity. Using an optimal inoculum
concentration and incubation time, percentage of
Mh1 adherence was compared on nasal, nasopharyngeal,
turbinate, and tonsillar mucosal tissue, and
adherence to nasopharyngeal tissue was confirmed
by scanning and transmission electron microscopy.
Results—The optimal Mh1 inoculum concentration
was 1 × 107 colony forming units/ml and incubation
time was 3 hours. Percentage of adherence of Mh1
to nasopharyngeal tissue was greater than adherence
to other tissue types.
Conclusions and Clinical Relevance—The ex vivo
model maintained the functional and structural integrity
of bovine upper respiratory tract mucosa, as confirmed
by light and electron microscopy. Electron
microscopy revealed participation of epithelial cell cilia
and surface mucus in adherence of Mh1 to nasopharyngeal
tissue. Adherence of Mh1 was confirmed in
repeated assays, indicating that this organism
adheres to upper respiratory tract mucosa of cattle.
(Am J Vet Res 2001;62:805–811)
Objective—To evaluate economic effects and health and performance of the general cattle population after exposure to cattle persistently infected (PI) with bovine viral diarrhea virus (BVDV) in a feedlot.
Animals—21,743 high-risk calves from the southeastern United States.
Procedures—PI status was determined by use of an antigen-capture ELISA (ACE) and confirmed by use of a second ACE, reverse transcriptase–PCR assay of sera, immunohistochemical analysis, and virus isolation from sera. Groups with various amounts of exposure to BVDV PI cattle were used. After being placed in the feedlot, identified PI cattle were removed from 1 section, but PI cattle remained in another section of the feedlot. Exposure groups for cattle lots arriving without PI animals were determined by spatial association to cattle lots, with PI animals remaining or removed from the lot.
Results—15,348 cattle maintained their exposure group. Performance outcomes improved slightly among the 5 exposure groups as the risk for exposure to BVDV PI cattle decreased. Health outcomes had an association with exposure risk that depended on the exposure group. Comparing cattle lots with direct exposure with those without direct exposure revealed significant improvements in all performance outcomes and in first relapse percentage and mortality percentage in the health outcomes. Economic analysis revealed that fatalities accounted for losses of $5.26/animal and performance losses were $88.26/animal.
Conclusions and Clinical Relevance—This study provided evidence that exposure of the general population of feedlot cattle to BVDV PI animals resulted in substantial costs attributable to negative effects on performance and increased fatalities.
Objective—To evaluate serum haptoglobin concentration at feedlot arrival and subsequent performance and morbidity and mortality rates of calves that developed bovine respiratory disease.
Animals—360 heifer calves and 416 steer and bull calves.
Procedures—Serum samples were obtained from cattle at the time of arrival to a feedlot (day −1) and analyzed for haptoglobin concentration. In experiment 1, calves were classified into groups with a low (< 1.0 μg/mL), medium (1.0 to 3.0 μg/mL), or high (> 3.0 μg/mL) serum haptoglobin concentration and allotted into pens on the basis of group. In experiment 2, calves were classified as having or not having detectable serum haptoglobin concentrations.
Results—In experiment 1, average daily gain from days 1 to 7 decreased as haptoglobin concentration increased. Dry-matter intake (DMI) from days 1 to 21 decreased with increasing haptoglobin concentration, and DMI typically decreased from days 1 to 63. Total bovine respiratory disease morbidity rate typically increased with increasing haptoglobin concentration. At harvest, no differences in carcass characteristics were observed on the basis of haptoglobin concentration. In experiment 2, cattle with measureable serum haptoglobin concentrations at arrival weighed less throughout the experiment, gained less from days 1 to 7, and had lower DMI from days 1 to 42. Overall morbidity rate was not different between groups, but cattle with detectable serum haptoglobin concentrations had higher odds of being treated 3 times.
Conclusions and Clinical Relevance—Serum haptoglobin concentration in cattle at the time of feedlot arrival was not associated with overall performance but may have limited merit for making decisions regarding targeted prophylactic treatment.
Objective—To evaluate diagnostic tests used for detection of bovine viral diarrhea virus (BVDV) and determine the prevalence of BVDV subtypes 1a, 1b, and 2a in persistently infected (PI) cattle entering a feedlot.
Procedures—Samples were obtained from calves initially testing positive via antigen capture ELISA (ACE) performed on fresh skin (ear notch) specimens, and ACE was repeated. Additionally, immunohistochemistry (IHC) was performed on skin specimens fixed in neutral-buffered 10% formalin, and reverse transcriptase PCR (RT-PCR) assay and virus isolation were performed on serum samples. Virus was subtyped via sequencing of the 5′ untranslated region of the viral genome.
Results—Initial ACE results were positive for BVDV in 88 calves. After subsequent testing, results of ACE, IHC, RT-PCR assay, and viral isolation were positive in 86 of 88 calves; results of all subsequent tests were negative in 2 calves. Those 2 calves had false-positive test results. On the basis of IHC results, 86 of 21,743 calves were PI with BVDV, resulting in a prevalence of 0.4%. Distribution of BVDV subtypes was BVDV1b (77.9%), BVDV1a (11.6%), and BVDV2a (10.5%).
Conclusions and Clinical Relevance—Rapid tests such as ACE permit identification and segregation of PI cattle pending results of further tests, thus reducing their contact with the rest of the feedlot population. Although vaccines with BVDV1a and 2a components are given to cattle entering feedlots, these vaccines may not provide adequate protection against BVDV1b.
Objective—To detect bovine adenovirus serotype 7
(BAV-7) infections in calves by use of viral isolation
and serologic testing.
Animals—205 postweaning calves.
Procedure—121 calves were assembled by an order
buyer through auction markets in eastern Tennessee
and transported to New Mexico where they were
commingled with 84 healthy ranch-reared calves.
Tests included viral isolation in cell culture from
peripheral blood leukocytes (PBL) and detection of
serum BAV-7 antibodies by use of microtitration viral
Results —BAV-7 was isolated from PBL of 8 calves
and seroconversion to BAV-7 was detected for 38 of
199 (19.1%) calves. Concurrent bovine viral diarrhea
virus infections were detected in most calves from
which BAV-7 was isolated.
Conclusions and Clinical Relevance —Results of our
study indicate that BAV-7 infections can be found in
postweaning commingled calves and may develop
more commonly in calves with concurrent infections
with viruses such as bovine viral diarrhea virus
(BVDV). (Am J Vet Res 2002;63:976–978).
Objective—To compare effects of administration of a modified-live respiratory virus vaccine once with administration of the same vaccine twice on the health and performance of cattle.
Design—Randomized, controlled trial.
Animals—612 mixed-breed male cattle with unknown health histories.
Procedures—Cattle were randomly assigned to 1 of 2 treatment groups (single vaccination treatment group [SVAC group] vs revaccination treatment group [REVAC group]) during the preconditioning phase of production. All cattle were given a modified-live respiratory virus vaccine. Eleven days later, REVAC group cattle received a second injection of the same vaccine. During the finishing phase of production, cattle from each treatment group were either vaccinated a third time with the modified-live respiratory virus vaccine or given no vaccine. Health observations were performed daily. Blood and performance variables were measured throughout the experiment.
Results—During preconditioning, no significant differences were observed in performance or antibody production between groups. Morbidity rate from bovine respiratory disease was lower for SVAC group cattle; however, days to first treatment for bovine respiratory disease were not different between groups. No significant differences in body weights, daily gains, or dry-matter intake between groups were observed during the finishing phase. Revaccination treatment group cattle had improved feed efficiency regardless of vaccination protocol in the finishing phase.
Conclusions and Clinical Relevance—Vaccination once with a modified-live respiratory virus vaccine was as efficacious as vaccination twice in the prevention of bovine respiratory disease of high-risk cattle, although feed efficiency was improved in REVAC group cattle during the finishing period.
Objective—To identify any adverse effects on health or performance in young dairy calves fed clinoptilolite mixed with milk replacer.
Animals—26 male Holstein calves (1 to 7 days old).
Procedures—Twice daily for 28 days, calves were fed milk replacer with no clinoptilolite (control group; n = 8), 0.5% clinoptilolite (low-dosage group; 9), or 2% clinoptilolite (high-dosage group; 9); each calf consumed approximately 12% of its body weight (based on the replacer solids in the milk replacer mixture)/d. For each calf, subjective health assessments, weight and rectal temperature measurements, and CBC and serum biochemical analyses were performed at intervals. All calves underwent necropsy.
Results—2 calves were euthanized during the experiment because of bronchopneumonia or enteritis. Body weight and average daily gain did not differ among treatment groups. The percentage of monocytes and serum total protein concentration in the low-dosage group were higher than values in the control and high-dosage groups. Compared with values for either clinoptilolite-treated group, BUN concentration was greater in the control group. Serum globulin concentration differed significantly among groups (2.77, 2.50, and 2.36 g/dL in the low-dosage, control, and high-dosage groups, respectively). At necropsy, gross lesions associated with clinoptilolite treatment were not detected in any of the calves.
Conclusions and Clinical Relevance—Even under stressful conditions, clinoptilolite fed at low or high dosages did not affect the performance of dairy calves and had no negative effect on WBC count and blood metabolite concentrations and enzyme activities. Clinoptilolite ingestion was not associated with treatment-specific gross changes.
Objective—To determine efficacy of a modified-live virus (MLV) vaccine containing bovine viral diarrhea virus (BVDV) 1a and 2a against fetal infection in heifers exposed to cattle persistently infected (PI) with BVDV subtype 1 b.
Animals—50 heifers and their fetuses.
Procedures—Susceptible heifers received a placebo vaccine administered IM or a vaccine containing MLV strains of BVDV1a and BVDV2a administered IM or SC. On day 124 (64 to 89 days of gestation), 50 pregnant heifers (20 vaccinated SC, 20 vaccinated IM, and 10 control heifers) were challenge exposed to 8 PI cattle. On days 207 to 209, fetuses were recovered from heifers and used for testing.
Results—2 control heifers aborted following challenge exposure; both fetuses were unavailable for testing. Eleven fetuses (8 control heifers and 1 IM and 2 SC vaccinates) were positive for BVDV via virus isolation (VI) and for BVDV antigen via immunohistochemical analysis in multiple tissues. Two additional fetuses from IM vaccinates were considered exposed to BVDV (one was seropositive for BVDV and the second was positive via VI in fetal tissues). A third fetus in the SC vaccinates was positive for BVDV via VI from serum alone. Vaccination against BVDV provided fetal protection in IM vaccinated (17/20) and SC vaccinated (17/20) heifers, but all control heifers (10/10) were considered infected.
Conclusions and Clinical Relevance—1 dose of a BVDV1a and 2a MLV vaccine administered SC or IM prior to breeding helped protect against fetal infection in pregnant heifers exposed to cattle PI with BVDV1b.