The aim of the study was to evaluate, under large-scale farm conditions, the prophylactic effect of various inactivated E. coli vaccines in the control of pig colibacillosis. The investigations were carried out with 2472 pregnant sows, immunized with 8 different vaccines containing E. coli fimbrial adhesins and adjuvants. Efficacy of the biologicals used was tested by evaluation of the health state of the newborn piglets, i.e. number of born and weaned piglets, percentage of piglets with diarrhea and dead piglets, and mean body weight gain of weaned piglets. It was also intended to check the influence of immunization on the number of pathogenic E. coli strains in the faeces of piglets originating from the vaccinated sows. The vaccines used in the study differed in their protective effect but all of them had a positive influence on the health status of the newborn piglets as well as on the reduction in the faeces of the number of pathogenic E. coli isolates. The best results were obtained when pregnant sows were immunized with a vaccine containing purified K88, K99, and 987P fimbriae and B subunit of LT enterotoxin. It seems that the determination of the number of pathogenic E. coli strains in the faeces of piglets originated from dams vaccinated against colibacillosis can be helpful in the evaluation of the vaccine efficacy.