Association Between Mycobacterium avium subsp paratuberculosis Fecal Shedding or Clinical Johne's Disease and Lactation Performance on Two Minnesota, USA Dairy Farms

Abstract

The scientific literature provides little information about the impact of Mycobacterium paratuberculosis shedding in dairy cattle on lactation performance, including the attributable reduction of milk production and productive longevity in the herd due to clinical and sub-clinical Johne's disease (JD). It is clear from the literature that JD infected cows are removed from the herd earlier in life than their non-infected herdmates. Many cattle with JD clinical signs are culled due to poor production even before a diagnosis of JD is confirmed, especially common in freestall housing where an individual cow's manure consistency is less obvious than in tiestall housing. Although several studies have considered the effect of JD on culling rate, none have addressed the impact of subclinical JD or fecal shedding level on the survival of the cow in the herd.
 Because of its economic importance, the impact of JD on milk production has been the most commonly evaluated effect of JD. Most studies have shown that JD-positive cows produce between 2-17% less milk than their negative herdmates, though the diagnostic test and the definition of positive cows varied between the studies. None of these studies have addressed the potential confounding impact of other factors, such as other clinical diseases, on this relationship.
 Few studies have estimated the impact of JD on reproductive performance. These studies have used different diagnostic testing methods, with some defining positive cows based on fecal culture or histology, and others using ELISA results. The lack of consistent associations in these studies may be explained by the variation of results from use of different diagnostic methods.