Paratuberculosis is endemic in the dairy cattle population of Germany. However, the actual prevalence on the individual animal as well as on the herd level is not known. A national paratuberculosis guideline came into force in February 2005 giving recommendations for paratuberculosis control on a voluntary basis. In Germany; because of the intensive cattle husbandry, paratuberculosis control in dairy cattle can only be successful combining strict hygienic measures in the herds with immediate removal of faecal shedders. Up to now, faecal culture is still the most sensitive method for the identification of faecal shedders, although it is expensive and time consuming. Improvement of the effectiveness of the identification of shedders is urgently needed.

It was the objective of the present study to clarify, whether the detection rate of faecal MAP shedders can be increased by optimising the time point of faecal sampling. Therefore, the influence of individual host factors on faecal shedding was investigated.

In two paratuberculosis positive dairy herds with an average of 245 (herd A) and 390 (herd B) lactating cattle, respectively, faecal samples were collected four times every 5 to 7 months from all lactating cows and heifers of more than 18 months of age. Bacteriological culture was performed for the detection of MAP. In herd A MAP positive animals were not removed systematically while in herd B, culling of shedders was performed regularly. Individual data of each animal included in the study were obtained from the herd records, i.e. age, lactation state, milk yield and others. For all animals with a culture positive faecal sample, individual factors at the respective time point were analysed for their contribution to the risk of faecal shedding.

In herd A, a higher proportion of faecal shedders were detected in older animals and in animals in the third trimester of lactation. In herd B, however, the influence of age and lactation state on faecal shedding was not obvious. In both herds, there was no clear relation between milk yield and the risk of faecal shedding. Analysing repeated sampling every 5 to 7 months, about 13.8 % of the shedders which underwent at least three faecal examinations would have been detected by one sampling, additional 16.6 % by two samplings and further 49.0 % by three samplings. 20.7 % of the shedders would not have been detected by three subsequent samplings.

In conclusion, individual factors that influence faecal shedding of MAP seem to be herd specific. In the present study, no general, preferential time point for sample collection could be identified. Although older animals may have a higher risk of MAP excretion, faecal culture is also successful in young dairy cattle and these animals should be examined too. One way to increase the detection rate of faecal shedders is repeated sampling.