Interpretation of repeated testing for Mycobacterium avium subsp paratuberculosis on Ontario dairy herds

Abstract

The Ontario Johne's Education and Management Assistance Program (OJEMAP) is a dairy industry-funded Johne's disease (JD) control program launched in January 2010. The program offers dairy producers a one-time opportunity to test their adult cow herd for antibodies against Mycobacterium avium subspecies paratuberculosis (MAP) by use of a milk or blood ELISA test. As herds completed their milking herd test, a common question from herd owners and veterinarians was "When should I test next .... how often should I test my herd?" A review of aggressive JD control programs around the world suggests that there are no standard recommendations regarding testing frequency. The Danish program, in existence for 7 years, is based on quarterly testing of the entire milking herd using a milk ELISA. Dr. Soren Nielsen, who developed the Danish Program and serves as its director, argues that given the relatively poor sensitivity of all JD tests, quarterly testing allows each cow to have at least 3 test results per year, the results of which can then be used to classify cows as at high-, moderate-, or low-risk for transmitting MAP to herd mates. Implementation of this strategy has led to a decrease in JD test-positive prevalence from 10% to 6% of cows in herds participating in the program. Unfortunately, this aggressive herd test program carries a high cost and the benefits of quarterly testing over a single annual test are difficult to quantify. The objective of this project was to evaluate and gain experience in the interpretation of repeated testing for MAP with currently available tests in Ontario dairy herds.