Temporal Repeatability of Positive Test Results of Mycobacterium avium subspecies paratuberculosis-antibody Milk ELISA-positive Cows

Johne’s disease (JD) of dairy cows is caused by Mycobacterium avium subspecies paratuberculosis (MAP). Although the majority of infected cows are subclinical, the infection causes production losses which lead to economic losses for the farm. Available tests do not identify all subclinically infected cows, and anecdotal reports from producers indicate that some cows can test positive for Johne’s disease or MAP antibodies at one test, and the same cow can test negative at a following test. These contradictory results often lead to frustration and uncertainty among producers about the interpretation of test results and their implication for JD control on their farm. Therefore, the objective of this study was to identify characteristics of the cow and her Dairy Herd Improvement (DHI) milk test at the time of a positive MAP-antibody milk ELISA (MAP milk ELISA) result that is followed by a different milk ELISA result, i.e. negative or suspect, compared to a cow’s milk test where cows tested positive at both the initial and subsequent MAP milk ELISA.