Abstract
In June 2018 an industry led initiative restricted the use of the highest priority,critically important antibacterials for human health (HP-CIAs): 3rd and 4th generation
cephalosporins (3GCs/4GCs) and fluoroquinolones (FQs) in dairy farms.
We collected faecal samples from pre-weaned and adult cows in 20 dairy farms in
England in 2020/21. Additionally, we collected samples from 21 Welsh dairy farms
from in 2022. We evaluated the prevalence of 3GC resistant (3GC-R) and FQ
resistant (FQ-R) positive samples and the associated molecular mechanisms in
Escherichia coli. Additionally, we held data collected from a previous study in
2017/18 for the same 20 dairy farms in England.
We studied the effect of the 2018 initiative on the prevalence of 3GC resistant (3GCR) and FQ resistant (FQ-R) positive samples and the associated molecular
mechanisms comparing the data collected in England in 2017/18 and in 2020/21
using a mixed effect logistic regression. We observed a significant reduction in
sample-level positivity rates for 3GC-R E. coli in the pre-weaned calves (p< 0.002).
This was driven by a significant reduction in sample-level positivity for E. coli carrying
CTX-M mechanisms of 3GC resistance (p<0.003) in this age group.
We also compared the data collected from the 2020/21 (English farms) and the 2022
study (Welsh farms) and observed that 3GC-R and FQ-R E. coli sample-level
positivity was similar. However, the prevalence of CTX-M mechanisms of 3GC-R in
the pre-weaned calves in Wales was significantly higher (p=0.02) than in England.
In the subgroup of 5 English farms we also studied management practices around
the birth and perinatal life of calves. We observed differences in cleanliness and biosecurity ranging from excellent to poor that had an impact on HP-CIA resistance with variations between farms and sites on each farm.
| Date of Award | 30 Sept 2025 |
|---|---|
| Original language | English |
| Awarding Institution |
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| Supervisor | Matthew B Avison (Supervisor) & Kristen K Reyher (Supervisor) |