Seroprevalence of Mycobacterium avium subsp paratuberculosis infection among dairy cows in Colorado and herd-level risk factors for seropositivity.

OBJECTIVE

To estimate seroprevalence of Mycobacterium avium subsp paratuberculosis (MAP) infection among adult dairy cows in Colorado and determine herd-level factors associated with the risk that individual cows would be seropositive.

DESIGN

Cross-sectional observational study.

ANIMALS

10,280 adult (> or = 2 years old) dairy cows in 15 herds in Colorado.

PROCEDURE

Serum samples were tested with a commercial ELISA. A herd was considered to be infected with MAP if results of mycobacterial culture of > or = 1 individual cow fecal sample were positive or if > or = 1 culled cow had histologic evidence of MAP infection.

RESULTS

424 of the 10,280 (4.12%) cows were seropositive. Within-herd prevalence of seropositive cows ranged from 0% to 7.82% (mean, 2.6%). Infection was confirmed in 11 dairies. Cows in herds that had imported > or = 8% of their current herd size annually during the preceding 5 years were 3.28 times as likely to be seropositive as were cows in herds that imported < 8%. Cows in herds with > or = 600 lactating cows were 3.12 times as likely to be seropositive as were cows in herds with < 600 lactating cows. Cows in herds with a history of clinical signs of MAP infection were 2.27 times as likely to be seropositive as were cows in herds without clinical signs.

CONCLUSIONS AND CLINICAL RELEVANCE

Annual importation rate, herd size, and whether cows in the herd had clinical signs typical of MAP infection were associated with the risk that individual cows would be seropositive for MAP infection.