Associations between subclinical Mycobacterium paratuberculosis infection and milk production, milk components, and somatic cell counts were studied in 23 Wisconsin dairy herds with a history of paratuberculosis infection and above-average production. All adult cows in the herds were tested for paratuberculosis by use of an absorbed ELISA, yielding 147 ELISA-positive and 1506 ELISA-negative cows. Milk yield, fat, protein, and somatic cell count data were retrieved electronically from DHI records. Regression analysis showed that ELISA-positive cows had a mature equivalent (ME) milk production of 376 kg (829 pounds) per lactation less than ELISA-negative herdmates based on least squares means (P=0.002). There was no significant difference in lactation average percent fat, protein, or somatic ell count linear score. When comparing ELISA-positive and negative cow's current ME milk with all previous lactations, there was a significant difference only from the previous lactation (P=0.001). When this difference was examined by parity group, significant difference was confined to cows in the second lactation (P=0.0003). The study showed that subclinical paratuberculosis infections, as determined by ELISA, are associated with a 4% reduction in milk yield.