A prospective, two group, cohort study was conducted to test the hypotheses that cows that are subclinically infected with M. paratuberculosis will have an increased number of days to first service and an increased number of days to conception, than their negative herd-mates. Blood and fecal samples were collected from all cows in their first lactation or 24 months of age and older. The IDEXX Enzyme Linked Immunosorbent Assay (ELISA) test and radiometric fecal culture were used to determine the Johne's status of each subject. Those cows that test positive on either the ELISA or radiometric fecal culture were identified as cases. For each case, three controls were selected from the same herd, matched on lactation number and phase of reproductive cycle. Analysis of the preliminary data (using the Kruskal-Wallis Chi-Square Approximation) has revealed that those cows that tested positive for Johne's disease had a mean of 141.5 days to conception, those cows that were negative had a mean 104.5 days to conception (p<0.05).