|Van kessel, Jo ann|
Submitted to: Journal of Dairy Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/21/2009
Publication Date: 5/15/2009
Publication URL: hdl.handle.net/10113/31769
Citation: Smith, R.L., Grohn, Y.T., Pradhan, A.K., Whitlock, R.H., Van Kessel, J.S., Smith, J.M., Wolfgang, D.R., Schukken, Y.H. 2009. A longitudinal study for the impact of Johne's Disease status on milk production in individual cows. Journal of Dairy Science. 92:2653-2661. Interpretive Summary: Johne’s disease is a chronic, progressive, infectious intestinal disease of cattle and is caused by infection with the bacterium, Mycobacterium avium subsp. paratuberculosis (MAP). A large number of U.S. dairy herds are infected with MAP and the dairy industry incurs large economic losses as a result of Johne’s Disease. MAP infection is characterized by a very long incubation period and identification of animals that are infected is very difficult. Data from a 4-year study of milk production and infection with Mycobacterium avium subsp. paratuberculosis (MAP) on three U.S. dairy herds were analyzed. Results showed that animals later diagnosed with Johne’s Disease produced more milk than uninfected animals, but the difference in milk production decreased over time and was lower in infected animals than in uninfected animals after diagnosis of Johne’s Disease. Infection with MAP, therefore, impacts dairy herds via decreased milk production. These results can be used to help the dairy industry establish an economically efficient MAP control program to decrease the prevalence of Johne’s Disease.
Technical Abstract: Longitudinal data from three commercial dairy herds in the Northeast United States were collected from 2004 to 2007. Johne’s Disease status, as indicated by Mycobacterium avium subsp. 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 Mycobacterium avium subsp. paratuberculosis. Cows infected with Mycobacterium avium subsp. 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 more than 30 cfu/gram produced approximately 4 kg less milk per day compared to uninfected cows. These results will be valuable in calculating the economic effect of Johne’s Disease.