Herd-level economic losses associated with Johne's disease on US dairy operations
Introduction
Johne's disease (paratuberculosis) is a chronic infectious disease of domestic and exotic ruminants, including dairy and beef cattle, sheep, goats, cervids, and camelids. The disease is caused by Mycobacterium paratuberculosis and occurs worldwide. M. paratuberculosis is a slow-growing bacterium that causes thickening of the intestinal wall of cattle; the thickening reduces absorptive capability. Johne's disease in cattle and other species is characterized by chronic, granulomatous degenerative enteritis that causes intermittent but persistent diarrhoea, progressive weight loss, and eventual death. The disease is untreatable and slowly progressive (Stehman, 1990).
On dairy farms, economic losses occur through premature culling, reduced milk production, and body-weight losses in slaughter cattle. In a recent summary of production studies by Nordlund et al. (1996), Johne's-infected cows produced from 2 to 19% less milk then their herdmates. These losses associated with Johne's disease led the dairy industry to request that economic analysis of Johne's disease be an objective for US Department of Agriculture (USDA) National Animal Health Monitoring Systems' (NAHMS) 1996 national dairy survey known as Dairy '96.
Section snippets
Dairy survey
In January 1996, the first phase of Dairy '96 began with an interview of a stratified random sample of 2542 dairy producers in 20 selected states (Fig. 1.). This survey represented 83% of US dairy cows and questionnaires were administered by USDA's National Agricultural Statistics Service enumerators to collect herd health and management information. Participating producers with at least 30 milk cows were asked to continue in the second phase of the study. During the second phase, USDA or state
Model results
Our results showed that Johne's disease can be costly to dairy producers (Table 1). In Model I, Johne's-positive herds when compared to Johne's-negative herds generated US$ 97 (US$ 1916 vs. US$ 2013, p < 0.01) per cow less in annual adjusted value of production (AAVP). In Model II, Johne's-positive herds with <10% cull cows reported showing clinical signs consistent with Johne's disease (low-clinical Johne's-positive herds) generated US$ 61 (US$ 1996 vs. US$ 2027, p = 0.08) per cow less in AAVP
Discussion
Cost of Johne's disease reported in six studies varies widely (Buergelt and Duncan, 1978; Whitlock et al., 1985; Chiodini and Van Kruiningen, 1986; Benedictus et al., 1987; Abbas et al., 1993; Meyer and Hall, 1994). To reduce the variation among the studies, costs were standardized to a common milk price and (when possible) to a common loss of reduced cull value for clinical cases. Using a milk price of US$ 286.60 per metric tonne (US$ 13 per cwt), estimated economic losses associated with
Acknowledgements
The authors would like to thank USDA National Agricultural Statistics Service for survey design and data collection; USDA Veterinary Services field staff for data collection; USDA Center for Animal Health Monitoring for survey design, questionnaire development, and data entry; and USDA National Veterinary Services Laboratories for testing sera for M. paratuberculosis.
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