Cristobal Verdugo, Maria Francisca Valdes, and Miguel Salgado from the Instituto de Medicina Preventiva Veterinaria, Facultad de Ciencias Veterinarias, Universidad Austral de Chile, Valdivia, Chile described herd level risk factors for Mycobacterium avium subsp. paratuberculosis (MAP) infection and clinical incidence in dairy herds in Chile. Their publication will appear in Preventive Veterinary Medicine, volume 176, March 2020 and is available online now (6 pages with 56 references). Unfortunately, it is not Open Access.
Holstein with clinical Johne’s disease photographed in Chile by M.T. Collins.
The study objective was to identify risk factors associated to: i) the infection by Mycobacterium avium subsp. paratuberculosis (MAP), and ii) paratuberculosis clinical incidence in Chilean dairy herds. A random sample of forty herds with previous history of MAP infection was selected. At herd level, all lactating cows were tested using a commercial ELISA kit. On the sampling date, a questionnaire gathering information on herd demographics, husbandry practices, and biosecurity measures was applied. Additionally, the farm manager/owner was surveyed regarding the number of paratuberculosis compatible clinical cases (CCC) in the last 12 months. Two Bayesian generalized linear mixed effect models were used to evaluate the association between the questionnaire data, and the proportion of truly infected animals (model 1) or the number of CCC (model 2).
A total of 4963 animals were sampled with an average apparent prevalence of 6.3 % (95 % confidence interval (4.0–8.0%). All sampled herds presented seropositive animals. Forty eight percent of the herds did not observe any CCC in the last year. Although, among those herd that did report CCC, a median of two cases per year was estimated. Model outputs showed that the proportion of truly infected animals and CCC reporting rates are associated to management practices. Specifically, positive associations were observed for feeding of calves exclusively with milk replacer, and the distance between the milking parlor and the calves’ barn. Additionally, CCC reporting rates were higher in farms that recently purchased animals, and where the distance between the milking parlor and the calves’ barn was less than 30 m.
Author’s Conclusions : “…the present research was able to find herd level factors associated to an increase in the risk of infection and the chances of reporting CCC. The reported factors put an emphasis on the need of introducing or improving basic biosecurity measures, especially in relation to the hygiene of calves, limiting the contact of young animals with manure from adult cows. The investment in such measures would not only be beneficial for MAP control but would improve the general health of the herd, possibly reducing the use of veterinary drugs.
Comment: The association of MAP infections with feeding calves milk replacer should be interpreted with caution. While milk replacer has been shown to harbor viable MAP (Grant 2017), it is also possible that preparation of the milk replacer on farms allowed fecal contamination which carried MAP into the re-hydrated product before feeding.