The National Animal Health Monitoring System's Dairy 2002 surveyed dairy operations in 21 states representing 82.8% of U.S. dairy operations and 85.5% of U.S. dairy cows. A subset of operations allowed collection of biological samples for fecal culture and serum- and milk-ELISA testing for Mycobacterium avium subspecies paratuberculosis (MAP) infection, and access to Dairy Herd Improvement Association production records. Mature equivalent (ME) milk production in the lactation in which testing occurred was evaluated using Proc Mixed in SAS. There were 2,832 cows from 23 herds evaluated using fecal culture results, 7,614 cows from 38 herds evaluated with serum ELISA and 11,874 cows from 33 herds using milk ELISA. Cows classified as heavy shedders produced significantly less ME milk compared to all other cows. Heavy MAP shedders produced almost 5,000 lbs less ME milk compared to moderate shedders and 8-9,000 lbs less than low, very low and culture negative cows. Cows that tested strong positive on serum ELISA produced 2,000 lbs less than test-positive cows and more than 2,500 lbs less than test-negative cows. For both ELISA testing methods, ME milk production was almost identical for each testing category. Cows that tested strong positive via serum ELISA produced significantly less ME milk in the current lactation compared to cows that tested positive, inconclusive or negative. The same was true for cows tested via milk ELISA. There were no significant differences in ME milk production between test-negative and test-positive cows for either ELISA. Results of this study suggest that the decline in milk production for cows with MAP infection occur in cattle that are shedding the largest number of bacteria or have developed the greatest immune response.