The effect of Mycobacterium avium ssp. paratuberculosis (MAP) on dairy reproduction and culling is among the least documented cost attributed to this infection. Research published in the August 2010 Journal of Dairy Science offers some insight to this influence.
To better understand the implications of MAP infections and Johne's disease in a dairy herd, the rates of calving and culling were calculated for cows in each stage of MAP infection relative to uninfected cows. Data from six commercial dairy herds, consisting of 2,818 cows with 2,754 calvings and 1,483 cullings, were used for analysis.
Every cow in each study herd was tested regularly for MAP, and herds were followed for between four and seven years. Johne's disease status, test-negative, low-positive (low-shedding or ELISA-positive only) or high-shedding, was defined as a time-dependent variable for all cows with at least one positive test result or two negative test results.
Not surprisingly, non-shedding animals were significantly less likely to be culled in comparison with animals in the low-shedding or ELISA-positive category.
The researchers also observed an increased calving interval in animals shedding high levels of MAP compared with low-positive animals.