Culture of Mycobacterium avium subspecies paratuberculosis (Map) from fecal samples is a key element in many paratuberculosis control programs. Contamination of fecal cultures by other bacteria and fungi at different stages of incubation is a major problem and results in the need to collect and culture new samples from the animals concerned. However, re-testing animals following contamination of fecal samples at a late stage of incubation may be rather inefficient. The likelihood that these animals are fecal shedders is reduced, because Map colonies were not detected at an earlier stage. Therefore, the results of re-sampling and culturing of feces of 2532 cattle after contamination of a previous individual culture were analyzed in a retrospective study over the period April 1997 - June 1999. Re-sampling was done within 12 months after the initial sampling. The employed fecal culture technique has been described previously. Of the 2532 contaminated initial samples, 16% were found contaminated at four weeks of incubation, 53% at 8 weeks, 14% at 12 weeks and 17% at 16 weeks. Re-testing of animals following contamination at 4, 8, 12 and 16 weeks of incubation resulted in detection of 2.5%, 5.8%, 0.84% and 1.8% culture positive animals respectively. The obtained results were applied to our rates of positive and contaminated individual fecal cultures in the period 1998 - 2000. Not re-testing animals following contamination after more than 8 weeks of incubation would have resulted in an estimated reduction of the rate of re-testing of 25%, while the estimated relative sensitivity of the individual fecal culture was still 98.5% in comparison to re-testing all animals following contamination. It is concluded that re-testing cattle following contamination of a fecal culture is not cost efficient if contamination occurs after more than 8 weeks of incubation.