Background

Map can be shed in milk and thus infect calves fed milk containing Map.

Objective

To evaluate the ability to detect cows shedding Map in milk based on a test scheme with ELISA and faecal culture.

Materials and Methods

Milk and faecal samples from 668 cows from six dairy herds were assessed in a test scheme with four annual herd screenings of milk and one annual herd screening of faecal samples. Milk samples were analysed for antibodies with ELISA and faecal samples were cultured for presence of Map. The cows were classified into three risk-groups defined as follows: 0) Low risk (never test-positive (ELISA or faecal culture)); 1) Medium risk: test-negative, but only tested once; 2) High risk: Test positive on at least one sampling. Presence of Map in milk samples was estimated by use of a peptide-mediated capture PCR (ISMav2-based).

Results

The cows were distributed in the risk groups as follows: 0) 386 cows; 1) 138 cows; 2) 144 cows. The PCR test was positive on milk samples from nine cows. None of these cows had diarrhoea or low body condition scores. Four were from risk group 0, one was from risk group 1, and four were from risk group 2.

Discussion

Four cows classified as low risk apparently had Map in their milk, and farmers would use their milk for feeding. Given the test-positive responses in the PCR were caused by Map-infection of the animals, these animals may pose a serious risk of further transmission of Map and the approach selected for classification of cows is insufficient. A major problem of this study is the unknown accuracy of the PCR. Contamination may have occurred during sampling, and the sensitivity is unknown.