Selection of resistant coliform bacteria in the intestine of pigs following flock versus individual treatment with neomycin against post-weaning diarrhoae or amoxicillin against umbilical infection

The aim of this study was to investigate the effect of avoiding flock treatment on resistance levels in the intestine of pigs. To investigate this, studies, each in two pig herds, quantified resistant coliforms by culture method in pigs treated as flock or as individual animal treatments orally with neomycin against post-weaning diarrhea (PWD) or intramuscularly with amoxicillin to prevent umbilical infection. Individual oral treatment against PWD did not lead to a lower number or proportion of resistant coliforms compared to flock treated pigs in any of the two herds under study, despite reduction of treatment incidences to 32% and 35% of pigs. After intramuscular treatment against umbilical infection, fewer resistant bacteria were seen in individually treated piglets in a herd with low treatment incidence (33%), while no reduction of resistant coliform bacteria compared to flock treatment was observed in the other herd with higher treatment incidence (86%). Thus, individual animal treatment reduced the amount of antimicrobial used, but concurrent reduction in resistant coliform bacteria was not always observed.