Parenteral antimicrobial
treatment results in the excretion of antimicrobial-resistant bacteria. Dairy
cows are commonly housed side by side in tie-stalls and often receive
antimicrobial treatment. However, studies investigating treated cows as source
of colonization of neighboring cows with resistant bacteria are scarce.
Antimicrobial resistance (AMR) in cows (treated and untreated) in tie-stalls was
investigated to assess their respective risks of carrying resistant bacteria.
Furthermore, we analyzed associations of farm management with AMR. Case-control
study: For isolation of indicator Escherichia (E.) coli, rectal swab
samples were taken. Cows were sampled depending on treatment history and proximity to one another (cow A: recently treated
parenterally; cow B: untreated, next to cow A; cow C: untreated, at
considerable distance from all treated cows). Antimicrobial susceptibility was
tested by microdilution. Associations of AMR with exposure to cow A, treatments,
and management were analyzed using generalized mixed-effects logistic models. Susceptibility
data on 571 isolates from 131 dairy farms were obtained. Almost no difference
in proportions of resistant E. coli was observed between cows B and C (B:
53.4%; C: 57.2%; P=0.52). Untreated cows had lower odds of carrying
resistant E. coli than treated cows (B: OR 0.44, P<0.001; C:
OR 0.54, P=0.007). Non-pansusceptibility of isolates was associated with
antimicrobial treatment (1 treatment: OR 2.11, P=0.001; ≥2: OR 1.76, P=0.043).
Using manure on forage crops was associated with higher
odds of pansusceptibility (OR 2.01, P=0.004). For daily practice, with
regard to the risk of AMR transmission, results of this study do not provide
evidence for the need to separate treated cows from others during treatment in
tie-stalls.