Associations between paratuberculosis status and milk production traits in Holstein cattle under consideration of interaction effects between test result and farm and lactation number

One of the most important factors for economic losses as result of infection with Mycobacterium avium ssp. paratuberculosis (MAP) is the decrease in milk yield. Different phenotyping methods for MAP lead to an inconsistent impact of MAP infection on milk parameters. It was the aim of the study to analyse the effect of the MAP status on milk yield, milk fat and milk protein (in kilograms), as well as on the calving interval and milk kilograms per day of life in German Holstein cattle. A dataset of 9 367 faecal culture tested animals from 14 farms in Thuringia (Germany) were available. The MAP status of the animals affected milk yield and the milk parameters. Beside the effects of farm, lactation number and MAP status, the interaction between MAP status and farm on the milk parameters was significant. The latter result is a possible explanation for the inconsistent results from recent studies. For milk kg per day of life, the interaction between lactation number and MAP status also showed significance.