Effect of Mycobacterium avium subsp. paratuberculosis infection status on culling and calving difficulty in dairy cattle

The present paper was designed to assess the effect of Mycobacterium avium subsp. paratuberculosis (MAP) infection status (antibody positive vs antibody negative, as measured by ELISA) on time to culling and calving difficulty in dairy cows. The study was carried out in 8 dairy farms in Galicia (north-west Spain). All of them were taking part in an ongoing paratuberculosis control program, as well as in a dairy herd improvement program. In order to estimate the relation between time to culling and MAP serological status of dairy cows, the present study followed the Andersen-Gill model for survival analysis. Similarly, in order to evaluate the influence on calving difficulty an ordinal logistic regression model was applied. The results indicated that seropositive cows were more likely to be culled due to death/urgent slaughter (hazard ratio=1.88), low productivity (hazard ratio=2.55), infertility (hazard ratio=4.64) and other causes (hazard ratio=1.67). Additionally, the probability of difficulties at calving time was 2.74 times higher for seropositive cows. The estimated effects could determine the economic benefits of a paratuberculosis control program.