Associations between subclinical paratuberculosis and milk production, milk components, and somatic cell counts in dairy herds

Objective-To determine associations between subclinical Mycobacterium paratuberculosis infection and milk production, milk components, and somatic cell counts oi dairy cattle. Design-Cross-sectional epidemiologic survey. Animals-23 dairy herds in Wisconsin containing 1,653 adult cows were studied. The herds had above average milk production and a history of bovine paratuberculosis in the herd within the previous 12 months. Procedure-All adult cows in the herds were tested for paratuberculosis by use of an absorbed ELISA. Milk yield, fat, protein, and somatic cell count data were retrieved electronically from Dairy Herd improvement Association records. Results-147 ELISA-positive and 1,506 ELISA-negative cows were identified. ELISA-positive cows had a mature-equivalent milk production of 376 kg (829 lb)/lactation less than that for ELISA-negative herdmates. Significant difference was not found in lactation average percentages; of fat and protein, or somatic cell count linear score. When comparing ELISA-positive and -negative cow's current mature equivalent milk with ail previous lactations, significant difference was found only from the immediate-preceding lactation. When this difference was examined by parity group, significant difference was confined to cows in the second lactation. Clinical Implications-Subclinical paratuberculosis infections, as determined by ELISA, are associated with a 4% reduction in milk yield and add to the already substantial costs of clinical M paratuberculosis infection in the dairy industry.