Age-related decline in carriage of ampicillin-resistant Escherichia coli in young calves

Comparison of the carriage of ampicillin-resistant Escherichia coli with age and time in multiple cohorts of calves sampled monthly from birth on four farms is done. The presence of ampicillin-resistant E.coli in older cattle on all farms suggests that in some calves the decline is transient, with cattle reacquiring resistant bacteria at a later point due to environmental changes or management events on the farm.