Comparison of calf weaning weight and associated economic variables between beef cows with and without serum antibodies against or isolation from feces of Mycobacterium avium subsp paratuberculosis.

OBJECTIVE: To compare calf weaning weight and associated economic variables for beef cows with serum antibodies against Mycobacterium avium subsp paratuberculosis (MAP) or from which MAP was isolated from feces with those for cows that were seronegative for antibodies against or culture negative for MAP. DESIGN: Retrospective study. ANIMALS: 4,842 beef cows from 3 herds enrolled in the USDA National Johne's Disease Demonstration Herd Project. PROCEDURES: Individual cow ELISA and culture results were obtained from the project database. During each parity evaluated for each cow, the 205-day adjusted weaning weight (AWW) of its calf was calculated. The AWW was compared between test-positive and test-negative cows by use of multilevel mixed-effect models. The median value for feeder calves from 2007 to 2011 was used to estimate the economic losses associated with MAP test-positive cows. RESULTS: The AWW of calves from cows with strongly positive ELISA results was 21.48 kg (47.26 lb) less than that of calves from cows with negative ELISA results. The AWW of calves from cows classified as heavy or moderate MAP shedders was 58.51 kg (128.72 lb) and 40.81 kg (89.78 lb) less, respectively, than that of calves from MAP culture-negative cows. Associated economic losses were estimated as $57.49/calf for cows with strongly positive ELISA results and $156.60/calf and $109.23/calf for cows classified as heavy and moderate MAP shedders, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Calves from cows with MAP-positive test results had significantly lower AWWs than did calves from cows with MAP-negative test results, which translated into economic losses for MAP-infected beef herds.