How long does antimicrobial resistance persist in calves
exposed to antimicrobials in either milk or systemic therapy?
Seventy-five calves recruited from 15 MN dairy farms. Part of the calves were exposed to antimicrobials either through their milk diet or systemic treatment. Other calves received no exposure. Estimates of antimicrobial resistance of fecal E. coli for all calves were made at weeks 1, 3, 5 and 16 weeks of age.
When comparing calves exposed and not exposed to antimicrobials they found highest resistance levels among 1 and 3 week old calves with somewhat lower resistance levels by week 5.
By week 16 the levels of antimicrobial resistance was virtually zero among all calves.
The authors conclude,
"These findings suggest that exposure to antimicrobials through milk diet or systemic therapy may result in a transient increase in resistance in fecal E. coli, but once the antimicrobial pressure is removed, suseptible E. coli are able to flourish again, resulting in an overall decrease in resistance." (p10,126)
Reference: Foutz, C.A. and Others, "Exposure to antimicrobials through the milk diet or systemic therapy is associated with a transient increase in antimicrobial resistance in fecl Escherichia coli of dairy calves." Journal of Dairy Science 101:10126-10141 November 2018