Decision trees for pathogen identification
Bovine respiratory disease (BRD) continues to be a leading cause of economic loss, hampered animal welfare and antimicrobial use in cattle operations, worldwide. To improve disease control and prevention and better target antimicrobial therapy, there is a growing interest in microbiological tests on respiratory samples. However, these tests are time consuming, cost money and sampling might compromise animal welfare. Therefore, the objective of this study by Lowie et al (2021) (Preventive Veterinary Medicine https://doi.org/10.1016/j.prevetmed.2021.105469) was to develop immediately applicable decision trees for pathogen identification in outbreaks of BRD based on circumstantial factors. Data from a cross sectional study, involving 201 outbreaks of BRD in dairy and beef farms in the northern part of Belgium between 2016 and 2019, were used. Pathogens were identified by a semiquantitative polymerase chain reaction (PCR) on a pooled non-endoscopic broncho-alveolar lavage sample from clinically affected animals. Potential risk factors of involved animals, environment, management and housing were obtained by enquiry. Classification and regression tree analysis was used for decision tree development with cross-validation. Different trees were constructed, involving a general three-group classification tree (viruses, Mycoplasma bovis or Pasteurellaceae family) and a tree for each single pathogen. The general three-group classification tree was 52.7 % accurate and had a sensitivity of 81.5% and a specificity of 52.2% for viruses, respectively 51.7% and 84.4% for M. bovis and 28.9% and 93.6% for Pasteurellaceae. The single-pathogen trees were more specific than sensitive: Histophilus somni (Se 25.8%; Sp 94.5%), Mannheimia haemolytica (Se 69.2%; Sp 70.6%), bovine coronavirus (Se 42.2%; Sp 89.6%) and bovine respiratory syncytial virus (Se 34.0%; Sp 96.6%). For Pasteurella multocida, M. bovis and parainfluenza virus type 3 no meaningful tree was obtained. The concept and trees are promising, but currently lack sensitivity and specificity to be a reliable tool for practice.
Meloxicam use in Caesarean section
Postoperative pain and inflammation are normal physiological reactions to Caesarean section. Their management in cattle have rarely been investigated. This surgical procedure negatively affects reproductive function with, for example, a reduction in fertility resulting in an increase in calving interval. In this multicentre clinical trial published by Mauffré et al (2021) (Theriogenology https://doi.org/10.1016/j.the-riogenology.2021.09.005) the objective was to evaluate the impact on reproductive performance of meloxicam injected before Caesarean section to manage postoperative pain and inflammation. One hundred and twenty-seven Charolais heifers were recruited from 47 farms in six French veterinary practices in the Burgundy region. The heifers underwent a non-elective standardised Caesarean section operation. Heifers were randomly assigned to one of two groups: meloxicam (n=66), intravenous meloxicam injection before surgery, or control (n=61). Reproductive performance and health information were recorded from the time of the Caesarean section to the next calving or to culling. Meloxicam administration before Caesarean section had no effect on the incidence of retained placenta (18.2% of treated vs 25.0% of control p=0.35). The pregnancy rate was higher in treated than in control cows (83.1% vs 67.8%, p=0.04 after multivariate analysis) and a survival analysis showed that the median calving interval was 35 days shorter in the meloxicam compared with the control group. A trend was also observed for culling rate to be lower in treated (4.7%) compared with control cows (13.3%, p=0.09). In conclusion, this study suggests that there is a beneficial effect of meloxicam administration before Caesarean section on reproductive performance in Charolais heifers.
Cattle-associated fluoroquinolone-resistance
The primary aim of an open access study published by Mounsey et al (2021) (Journal of Anti-microbial Chemotherapy https://doi.org/10.1093/jac/dkab310) was to test whether cattle-associated fluoroquinolone-resistant (FQ-R) Escherichia coli found on dairy farms are closely phylogenetically related to those causing bacteriuria in humans living in the same 50 x 50 km geographical region suggestive of farm–human sharing. Another aim was to identify risk factors for the presence of FQ-R E. coli on dairy farms. FQ-R E. coli were isolated during 2017–2018 from 42 dairy farms and from community urine samples. Forty-two cattle and 489 human urinary isolates were subjected to whole genome sequencing, allowing phylogenetic comparisons. Risk factors were identified using a Bayesian regularization approach. Of 489 FQ-R human isolates, 255 were also third-generation-cephalosporin-resistant, with strong genetic linkage between aac(6’)Ib-cr and blaCTX-M-15. Possible farm–human sharing for pairs of ST744 and ST162 isolates were identified, but minimal core genome single nucleotide polymorphism (SNP) distances were larger between farm–human pairs of ST744 and ST162 isolates (71 and 63 SNPs, respectively) than between pairs of isolates from different farms (7 and 3 SNPs, respectively). Total farm fluoroquinolone use showed a positive association with the odds of isolating FQ-R E. coli, while total dry cow therapy use showed a negative association. In conclusion, this work suggests that FQ-R E. coli found on dairy farms have a limited impact on community bacteriuria within the local human population. However, reducing fluoroquinolone use may reduce the on-farm prevalence of FQ-R E. coli and this reduction may be greater when dry cow therapy is targeted to the ecology of resistant E. coli on the farm.