|Van Kessel, Jo Ann|
|Van Tassell, Curtis - Curt|
Submitted to: Joint Meeting of the ADSA, AMSA, ASAS and PSA
Publication Type: Abstract Only
Publication Acceptance Date: 2/15/2008
Publication Date: 7/8/2008
Citation: Zanella, R., Settles, M., Fyock, T., Whitlock, R., Schukken, Y., Van Kessel, J.S., Karns, J.S., Hovingh, E., Smith, J., Van Tassell, C.P., Gaskins, C., Neibergs, H. 2008. Heritability of Genetic Tolerance to Johne’s Disease. Joint ADSA-ASAS Meeting, July 7th-11th, 2008, Indianapolis, Indiana. p.4. Interpretive Summary:
Technical Abstract: Johne’s disease, also known as paratuberculosis, is a prevalent and economically important disease in cattle caused by bacterial infection of Mycobacterium avium subsp. paratuberculosis(MAP). Johne’s disease often results in weight loss, lowered milk production, and death. MAP is excreted in feces and milk of infected animals which helps propagate the disease. Infection generally occurs in neo-natal calves, but clinical disease and detection are often delayed for 2 to up to 6 years, prolonging the exposure of the herd to MAP. Disease prevalence is estimated to be present in 75% of US dairy herds and is increasing. Current vaccination and treatments are ineffective and diagnostic methods detect less than 25% of infected animals, at one time. Cattle exposed to MAP may have three distinct responses: failure to develop disease (resistant animals), disease with little fecal shedding of MAP (tolerant), or disease with significant fecal shedding (intolerant-susceptible animals). The objective of this study was to determine the heritability of genetic tolerance to Johne’s disease in 4 Holstein dairy herds. Genetic tolerance was determined by sequential diagnostic testing of 260 animals every 3-6 months followed by post mortem tissue examination. This testing regime represents the gold standard for Johne’s diagnosis. MAP testing was conducted on a minimum of 4 tissue samples per animal. Comparison of fecal and tissue testing results was used to determine if cows were classified as resistant, tolerant or intolerant-susceptible. Heritability was calculated using an animal method. Selection of animals with genetic tolerance to Johne’s would be advantageous by lowering infection pressure and extending the period between infection and clinical symptoms.