Relationships between clinical and pathological signs of disease in calves infected with Mannheimia (Pasteurella) haemolytica type A1

Implementing Precision Antimicrobial Therapy for the Treatment of Bovine Respiratory Disease: Current Limitations and Perspectives

The therapeutic efficacy of an early treatment protocol with an infection-stage adjusted fluoroquinolone regimen was evaluated in a field study on young bulls (YBs) presenting signs of bovine respiratory disease (BRD). A total of 195 YB (Charolais, Limousin, and Rouge-des-Prés breeds) from 6 farms implementing or not prophylactic antimicrobial treatments (PROPHY or absence) were randomly assigned to 1 of 2 experiment groups based on time of detection of BRD and first-line marbofloxacin regimen, early adjusted dose [Early 2 (E2)] or late standard dose [Late 10 (L10)]. Each YB was administered orally a reticulo-rumen bolus, allowing continuous monitoring of ruminal temperature. In the E2 group, YB presenting early signs of BRD, i.e., an increase in ruminal temperature over 40.2°C and persisting more than 12 h, confirmed by a clinical examination showing no or mild signs of BRD, were given 2 mg/kg of marbofloxacin. In the L10 group, YBs presenting moderate or severe signs of BRD at visual inspection, confirmed at clinical examination, were given 10 mg/kg of marbofloxacin. If needed, YBs were given a relapse treatment. The YBs were followed for 30 days. The proportions of first and relapse treatments were calculated, as well as the therapeutic efficacy at day 10. In the E2 group, the first-line treatments’ proportion was significantly higher (P < 0.05), while the relapse treatments’ proportion tended to be higher (P = 0.08), than in the L10 group. Evolution of clinical scores (CSs) of diseased YB was followed for 10 days. In both groups, CS and rectal temperature decreased significantly 24 h after treatment (P < 0.05). Treatment incidences (TI) representing antimicrobial consumption assessed on used daily doses (UDD) were calculated. Antimicrobial consumption of marbofloxacin and relapse treatments were not significantly different between the groups. These values were strongly influenced by the recourse to a prophylactic antimicrobial treatment, accounting for more than 90% of the antimicrobial amount in the herds implementing prophylaxis. The higher number of treatments in the groups treated on the basis of ruminal temperature monitoring, the accuracy of the detection method, and the necessary conditions to implement precision antimicrobial therapy in the field are discussed in this article.

Use of three-dimensional accelerometers to evaluate behavioral changes in cattle experimentally infected with bovine viral diarrhea virus

OBJECTIVE To assess the use of 3-D accelerometers to evaluate behavioral changes in cattle experimentally infected with a low-virulent strain of bovine viral diarrhea virus (BVDV). ANIMALS 20 beef steers (mean weight, 238 kg). PROCEDURES Calves were allocated to a BVDV (n = 10) or control (10) group. On day 0, calves in the BVDV group were inoculated with a low-virulent strain of BVDV (4 × 10(6) TCID50, intranasally), and calves in the control group were sham inoculated with BVDV-free medium (4 mL; intranasally). An accelerometer was affixed to the right hind limb of each calf on day -7 to record activity (lying, walking, and standing) continuously until 35 days after inoculation. Baseline was defined as days -7 to -1. Blood samples were collected at predetermined times for CBC, serum biochemical analysis, virus isolation, and determination of anti-BVDV antibody titers. RESULTS All calves in the BVDV group developed viremia and anti-BVDV antibodies but developed only subclinical or mild disease. Calves in the control group did not develop viremia or anti-BVDV antibodies. Mean time allocated to each activity did not differ significantly between the BVDV and control groups on any day except day 8, when calves in the BVDV group spent less time standing than the calves in the control group. Following inoculation, calves in both groups tended to spend more time lying and less time walking and standing than they did during baseline. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that behavioral data obtained by accelerometers could not distinguish calves subclinically infected with BVDV from healthy control calves. However, subtle changes in the behavior of the BVDV-infected calves were detected and warrant further investigation.

Determination of the duration of antibacterial efficacy following administration of gamithromycin using a bovine Mannheimia haemolytica challenge model

The antibacterial efficacy of gamithromycin administered once 1, 5, or 10 days prior to a challenge infection with Mannheimia haemolytica serotype A1 was evaluated. Forty calves were randomly allocated on day -11, restricted by body weight, to one of three treatment groups given gamithromycin at 6 mg/kg of body weight 10, 5, or 1 days before challenge or to an untreated control group. M. haemolytica A1 challenge infections were induced on day 0 by depositing 7.4 × 10(7) CFU at the bifurcation of the main bronchus using a bronchoscope. Clinical observations were made daily from the day of allocation to day 10, when necropsy was scheduled; three calves died or were euthanized in extremis on welfare grounds prior to scheduled necropsy. At necropsy the lungs were removed, pneumonic lesions were scored, and samples of lung tissue were cultured for M. haemolytica. The three groups of animals treated with gamithromycin before challenge had significantly lower lung M. haemolytica counts and fewer clinical signs of respiratory disease than did the saline-treated group. For most of the clinical parameters, the pattern of responses differed significantly (P < 0.05) between the gamithromycin-treated groups and the control group. There were no statistically significant differences between groups in the mean lung lesion scores, partly as a result of high individual variability, particularly within the control group. The administration of gamithromycin 1, 5, and 10 days prior to M. haemolytica A1 challenge resulted in a reduction in bacterial isolation from the lungs and a reduction in the severity of clinical disease.

Safety and efficacy testing of a novel multivalent bovine bacterial respiratory vaccine composed of five bacterins and two immunogens

Bovine bacterial respiratory diseases have been one of the most serious problems due to their high mortality and economic loss in calves. The vaccinations of bovine bacterial respiratory vaccines have been complex because of no multivalent vaccine. In this study, novel multivalent bovine bacterial respiratory vaccine (BRV) was developed and tested for its safety and efficacy. BRV was composed of two immunogens and five bacterins. These were leukotoxoid and bacterin of Mannheimia haemolytica type A, outer membrane protein and bacterin of Pasteurella multocida type A, and bacterins of Haemophilus somnus, Mycoplasma bovis, and Arcanobacterium pyogenes. ELISA antibody titers to five bacterial antigens in vaccinated guinea pigs increased, compared with those in unvaccinated ones. BRV was safe for calves and pregnant cattle in this study. In calves challenged with M. haemolytica and P. multocida, the average daily weight gain and antibody titers of vaccinated calves increased, and respiratory symptoms (P<0.05) and treatment frequency (P<0.01) of vaccinated calves significantly decreased, compared with those of unvaccinated calves. Interestingly, the antibody titers of M. haemolytica leukotoxoid and Mycoplasma bovis were closely related with the reduction of respiratory symptoms. BRV would be an ecomonical measure for the protection against bovine bacterial respiratory diseases.

Gelatinolytic matrix metalloproteinases-2 and -9 in tracheobronchial lavage fluid obtained from calves with concurrent infections of Pasteurella multocida and Mycoplasma bovirhinis

OBJECTIVE

To study gelatinolytic matrix metalloproteinases (MMPs) in tracheobronchial lavage fluid (TBLF) obtained from clinically normal calves and calves with Pasteurella multocida infection.

SAMPLE POPULATION

Samples of TBLF obtained from 11 calves with clinical signs of respiratory tract disease and growth of P multocida and Mycoplasma spp during culture of TBLF and samples of TBLF from 6 clinically normal calves with no bacterial growth during culture of TBLF.

PROCEDURE

MMPs in TBLF were analyzed by use of gelatin zymography. Gelatinases were identified on the basis of molecular weights and inhibition by EDTA.

RESULTS

The main gelatinolytic MMPs detected were the proform (90 to 110 kd) and active form (75 to 85 kd) of MMP-9 (gelatinase B) and the proform (67 to 75 kd) and active form (< 65 kd) of MMP-2 (gelatinase A). Increased amounts of active MMP-2 and MMP-9 were detected in TBLF of calves with respiratory tract disease, compared with amounts of active MMP-2 and MMP-9 in TBLF of clinically normal calves. Concurrent infection with Mycoplasma bovirhinis in calves with pneumonia attributable to P multocida was associated with higher concentrations of MMP-9.

CONCLUSIONS AND CLINICAL RELEVANCE

The host response to P multocida includes increases in MMP-2 and MMP-9 concentrations in TBLF. Greater amounts of MMPs detected in calves with concurrent M bovirhinis and P multocida infection indicates synergism between these organisms.