Investigation of the comparative sensitivity of serum, colostrum and whey for the detection of specific antibodies in sheep vaccinated against Johne's disease

Johne's disease is characterised by a long incubation period, and the sensitivity of serological tests against Mycobacterium avium subspecies paratuberculosis (MAP) is low during the subclinical stage of infection. Due to the relatively high concentration of immunoglobulins present in colostrum, testing of this sample might improve diagnostic test sensitivity and detection of infected animals. Blood, colostrum and whey samples were analysed from 26 vaccinated Merino-cross ewes and were tested for antibodies against MAP by indirect enzyme-linked immunosorbent assay (ELISA). At the recommended dilution for serum (1:20), the diagnostic sensitivity (DSe) of colostrum and whey were significantly higher compared to serum, but not significantly different from each other. The significant improvement in DSe when using colostrum compared to serum suggests that it might be possible to detect a greater proportion of infected animals using this sample.