Milk production in 1,706 cows from 14 dairy herds with M. paratuberculosis infection was monitored using Dairy Herd Improvement Association (DHIA) records. All cows in each herd were tested on an annual or semiannual basis using the fecal culture test. Milk production and infection status were monitored from July 1, 1987 to January 1, 1992. Lifetime, last lactation, and second-to-last lactation milk production parameters of culture-positive animals were compared with those of culture-negative cows. The majority of infected cows (n=253) were not exhibiting clinical signs of Johne's disease. Mean total lifetime production in the culture negative cows was 41,231 lb (18,741 kg) compared to 36,442 lb (16,564 kg) for the infected cows, but the difference was not statistically significant. Average daily milk production for the infected cows (48.2 lb, 21.9 kg) was significantly less (P less than 0.02) than that of uninfected cows (50.8 lb, 23.1 kg). Daily milk fat and milk protein production were also significantly less for the infected cows. Projected or actual 305 day production (mature equivalent) for the last lactation of infected cows (17,098 lb, 7,772 kg) was significantly (P less than 0.01) less than uninfected cows (18,502 lb, 8,410 kg). In the second to last lactation, the infected cows produced 400 lb (180 kg) less milk than the uninfected cows, but the difference was not significant (P greater than 0.09). These findings demonstrate that cows with M. paratuberculosis infection produce significantly less milk than uninfected cows, but the majority of the milk production loss is suffered in the final lactation.