In 1995 the objective was formulated to stop the spread of paratuberculosis in dairy herds in the three northern provinces of The Netherlands. This objective was striven after by formation of a group of dairy herds unsuspected from paratuberculosis, thus providing safe replacement animals to others. Selection of the herds was based on two criteria: (1) absence of clinical paratuberculosis in the last five years, declared by both herdsman and veterinarian and (2) closed herd management since three years. Strategic pooled faecal culture of all adult cows (>24 months) was performed at six months intervals. Hundred and thirteen herds were selected. Herd size varied from 20 to 280 adult dairy cows. The first examination was a check of the laboratory records of the Dutch Animal Health Service. Thirteen herds were suspected of paratuberculosis because of registered positive test results from individual blood or faecal samples in the preceding 5 years. This was in contradiction with the farmer- and veterinarian declaration. The hundred remaining herds entered the culture program. From these 100 herds respectively 13, 8, 10 and 9 herds were removed from the program because of culture of Mycobacterium paratuberculosis (Mptb) in the pooled faecal samples in the four subsequent herd cultures. The results of these 40 herds are presented in the table.



Besides the 13 herds that were excluded from the program after checking the registered laboratory records from the past, and the 40 herds that were positive at pooled faecal herd culture, another three herds had to be removed from the program because of closing down the herd or introducing animals of herds with a unknown paratuberculosis status. This means that from 113 participants after a two year program only 57 herds remained. Contamination of faecal cultures was responsible for a lower reliability of the negative culture results in three of these herds. Conclusions were: (1) Absence of clinical signs, as declared by the herdsman and confirmed by the practicing veterinarian, is no guarantee about the absence of Mptb infections in the herd. (2) Culture of pooled faecal samples was able to detect Mptb infections in a large proportion of herds unsuspected of paratuberculosis. (3) Repeated cultures of strategic pooled faecal samples in combination with closed herd management were needed to exclude Mptb infections in unsuspected dairy herds. The question how often cultures had to be repeated before herds could be declared free from paratuberculosis could not be answered from these results.