Aims

To investigate whether on-farm antibacterial usage (ABU), environmental antibacterial-resistant (ABR) Escherichia coli prevalence, sampling and sample handling methodologies are associated with ABR E. coli positivity in individual faecal samples from dairy heifers.

Methods and Results

Three hundred and sixty-four heifers from 37 farms were sampled via rectal or faecal pat sampling. Samples were stored at -80°C for variable periods before microbiological analysis. Data analysis was through a multilevel, multivariable logistic regression approach.

Individual rectal samples had increased odds of positivity for amoxicillin-, cefalexin- and tetracycline-resistant E. coli. Sample storage for 6-12 months was associated with decreased odds of finding amoxicillin- and tetracycline-resistant E. coli. On-farm ABU had little influence, and environmental ABR E. coli prevalence had no significant influence on the odds of sample-level positivity for ABR E. coli.

Conclusions

Sampling methodology and sample handling have a greater association than on-farm factors with the detection of ABR E. coli in individual faecal samples from dairy heifers.

Significance and Impact of the Study

Sampling and storage methodologies should be considered carefully at the point of designing ABR surveillance studies in livestock and their environments and, where possible, these methodologies should be standardised between and within future studies.