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A longitudinal study on the impact of Johne’s disease status on milk production in individual cows

R. L. Smith^*,1, Y. T. Grohn^*, A. K. Pradhan, R. H. Whitlock, J. S. Van Kessel, J. M. Smith^#, D. R. Wolfgang^|| and Y. H. Schukken

^* Section of Epidemiology and
Quality Milk Production Services, Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14850
New Bolton Center, Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Kennett Square 19348
Environmental Microbial Safety Laboratory, ANRI, USDA-ARS, Beltsville, MD 20705
^# Department of Animal Science, University of Vermont, Burlington 05405
^|| Department of Veterinary and Biomedical Science, Penn State University, University Park 16802

¹ Corresponding author: rls57{at}cornell.edu

Longitudinal data from 3 commercial dairy herds in the northeast United States were collected from 2004 to 2007. Johne’s disease status, as indicated by Mycobacterium avium ssp. paratuberculosis infection levels, was determined through quarterly ELISA serum testing, biannual fecal culture, and culture of tissues at slaughter. Milk production data were collected from the Dairy Herd Improvement Association. The effect of Johne’s disease status on milk production was analyzed using a mixed linear model with an autocorrelation random effect structure. Infected animals produced more milk than uninfected cows before they began shedding M. avium ssp. paratuberculosis. Cows infected with M. avium ssp. paratuberculosis had monthly decreases of 0.05 to 1 kg in daily milk production relative to uninfected animals, with greater decreases in progressive disease categories. Animals with fecal culture results of >30 cfu/g produced approximately 4 kg less milk per day compared with uninfected cows. These results will be valuable in calculating the economic effect of Johne’s disease.

Key Words: Johne’s disease • milk production