Background

It is widely accepted that most infections caused by Mycobacterium avium subsp. paratuberculosis (MAP) occur in utero or in the neonatal animal. The challenge, however, has been to demonstrate and detect the infection in the young animal, as the onset of clinical signs often takes several years. Earlier detection may allow for more prudent animal management decisions.

Objectives

The objectives of this study are to determine whether: 1) fecal shedding of MAP can be detected in naturally infected young animals, 2) there is a association between culture results and ELISA test scores, 3) there is a relationship between MAP shedding cows and fecal shedding in their offspring, and 4) pooled fecal sample testing is sensitive enough to detect MAP in calves.

Study Design

Longitudinal, prospective study of two years duration with more than 1,600 samples.

Materials and Methods

This study looks at dairy calves of four age groups from seven herds scattered throughout Lower Michigan with varied MAP prevalence and management styles.Fecal, and blood samples, are obtained. Calves from positive dams (fecal or ELISA) are targeted; calves from test negative dams fill out group and the test interval is three months. Serial testing "high risk" calves (from positive dam) is a priority. The TREK ® liquid culture system is used for fecal culture and the Biocor Paracheck ELISA for blood. Positive fecal cultures are confirmed with acid fast staining and IS900 PCR.

Preliminary Results

Results are in the early stages (240 samples), but we have detected shedding in eight calves representing all four age groups from 5 of the 7 farms. Also, five of the positive fecal results were seen in calves with a test-positive dam. A pool of ten containing one of the eight positives also tested positive. Seven positive ELISA samples have been reported.