Adaptation of a commercial ELISA for the detection of antibodies against Neospora caninum in bovine milk

The aim of the present study was to determine whether a commercially available ELISA could be used to examine bovine milk for antibodies against Neospora caninum. In an initial titration experiment, a milk dilution of 1:2 was found optimal to obtain milk results that were linearly correlated to those obtained with corresponding sera. This dilution was then used to examine 791 milk samples from N. caninum infected herds in the commercial ELISA. Milk results of individual animals were compared with those obtained by the same ELISA for the corresponding serum samples. The linear correlation between milk and serum antibody results of individual animals was characterized by R2=0.702. Multiple linear regression indicated that the later the stage of lactation at which an animal was sampled, the higher the milk ELISA result was as compared to the serum ELISA result. The examination of the two-graph receiver operating characteristics revealed an optimal cut-off of 0.261 to obtain similar results in the examination of milk and serum. With this cut-off, the test had a sensitivity and specificity relative to the serum results of 90%. The milk-based commercial ELISA classified more aborting dams as positive than the serum-based ELISA with this cut-off. The milk ELISA may be a valuable tool to assess the herd status with regard to abortion caused by N. caninum.