4d.Progress report.
This report serves to document research conducted under a Specific Cooperative Agreement (SCA: 58-1265-3-0155) between ARS and the University of Pennsylvania. Additional details of research can be found in the report for the parent project 1265-32000-074-00D titled "Dairy Management Practices and the Transmission of Zoonotic Pathogens".

This cooperative agreement is part of a larger project involving 4 universities, the University of Pennsylvania, The Pennsylvania State University, University of Vermont, and Cornell University, and formulated in consultation with the Northeastern Regional Dairy Quality Alliance (RDQMA) and the National Milk Producers Federation. Currently, this project provides longitudinal access to three dairy herds totaling 575 milk cows (NY herd-340 milk cows; PA herd-110 milk cows and VT herd-125 cows). The feces of each adult cow is culture tested twice a year for the presence of Mycobacterium avium Paratuberculosis (the causative agent of Johne’s disease) and blood serum is tested quarterly with an ELISA for the presence of antibodies to the Johne’s Disease (JD) organism. Frequency of fecal sampling is increased to quarterly for any cow previously identified as culture positive or ELISA positive. As adult milk cows are culled from the herd, attempts are made to retrieve fecal samples and tissues at slaughter for culture to provide further evidence of JD. After two fecal sampling cycles there is sufficient information to determine the current JD prevalence in each herd. The prevalence in each herd are as follows. Herd A: 2.6 to 2.8%; Herd B: 1.8% to 6.8%; and Herd C: 13.6%, for a total number of 41 culture positive out of 575 or 5.9% apparent prevalence across the study. All herds have been sampled up to four times for blood serum using an ELISA test. Four cows were identified as likely ‘super-shedders’ and one cow progressed from a low-moderate shedder to a ‘super-shedder’ over an 8 month time period. Based on the numerical assessment of Johne’s bacteria in colony forming units per gram of manure, a single ‘super-shedder’ could contaminate the environment with more bacteria than 160 heavy shedders, more than 6,000 moderate shedders and more than 60,000 low shedders. Preliminary investigations reveal that each of the three herds in the study have a super-shedder cow at their farm. Not only do these super-shedders contribute to environmental contamination and risk of disease transmission on the farm, they may also cause false-positive fecal culture results in uninfected cows because of gastrointestinal “pass through” of Johne’s bacteria. In the next year, the importance of ‘super-shedders’ for the transmission of JD in these dairy herds will be studied. Based on these results, management practices can be devised to further reduce the prevalence of JD in these and other dairy herds.