Although colostrum has been used to detect specific immunoglobulin (Ig) G to Mycobacterium avium subsp. paratuberculosis (MAP) in cattle, confounding, non-specific reactions can be a problem. The objectives of this study were to determine the proportion of non-specific ELISA reactions in samples of colostrum taken between 0 and 4days-in-milk (DIM), and to assess the probability of an animal testing positive for MAP specific IgG over this time-period. Non-specific reactions were found in 3/365 (0.8%) of samples. The odds of an animal testing positive on day of calving were 130 times higher than at 4 DIM. The findings suggest colostral samples may have enhanced diagnostic potential over milk samples in determining if cattle have been exposed to or infected with MAP.