Reduction in milk yield associated with Mycobacterium avium subspecies paratuberculosis (Map) infection in dairy cowsFrançois Beaudeaua, Maud Belliarda, Alain Jolyb and Henri Seegersa
a Unit of Animal Health Management, Veterinary School-INRA, BP 40706, 44307 Nantes Cedex 03, France
b UBGDS, BP110, 56000 Vannes Cedex, France
(Received 3 April 2006; accepted 9 March 2007 ; published online 13 June 2007)
Abstract - To assess the profitability of control schemes for Mycobacterium avium subspecies paratuberculosis (Map)-infection implemented in dairy herds, accurate estimates of its production effects are needed. This study aimed at quantifying the variation in milk yield of dairy cows according to their Map-infection status. The cow-status was determined by combining (i) its testing(s)-result(s) (serum ELISA, faecal culture (FC), PCR, Ziehl staining), (ii) the Map-status of its herd, and (iii) its possible vaccination against Map. A total of 15 490 cows in 569 herds located in western France was considered. The effect on test-day milk yield (TDMY) of the cow-status to Map was assessed separately in parity 1, 2 and 3 or more, using mixed linear models, after adjustment for herd-season (random), days in milk and breed. Average TDMY was significantly lower in cows from herds with at least one Map-infected cow (defined as positive herds). Individual TDMY showed a reduction ranging from 1.58 to 3.30, 2.03 to 2.51, 5.36 to 7.20 kg/day (P < 0.001) depending on parity for unvaccinated cows and testing ELISA-positive, PCR- or FC-positive, and Ziehl-positive, respectively, compared to cows in Map-free herds. The loss in milk yield increased with increased parity in ELISA-positive and Ziehl-positive cows. Cows that were both tested ELISA-positive and vaccinated had a smaller loss in TDMY than those that were unvaccinated. The estimates from this study can be used to further assess the economic impact associated with Map-infection in dairy herds or to help in the culling decisions regarding infected cows.
Key words: dairy cow / milk yield / Mycobacterium avium subsp. paratuberculosis
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© INRA, EDP Sciences 2007