Risk of removal and effects on milk production associated with paratuberculosis status in dairy cows.

Objective: To determine effects on production and risk of removal related to Mycobacterium avium subsp paratuberculosis (MAP) infection at the individual animal level in dairy cattle.
Design: Longitudinal study.
Animals: 7,879 dairy cows from 38 herds in 16 states.
Procedure: A subset of dairy cattle operations that participated in the National Animal Health Monitoring System Dairy 2002 study was evaluated via a serum ELISA for antibodies against MAP and categorized according to ELISA score. Dairy Herd Improvement Association records were obtained to collect current and historical lactation data and removal (ie, culling) information. Production variables were evaluated on the basis of serum ELISA category.
Results: Cows with strong positive results had mature equivalent (ME) 305-day milk production, ME 305-day maximum milk production, and total lifetime milk production that were significantly lower than cows in other categories. No differences were observed for ME 305-day fat and protein percentages, age, lactation, and lactation mean linear somatic cell count score between cows with strong positive results and those with negative results. After accounting for lactation number and relative herd-level milk production, cows with strong positive results were significantly more likely to have been removed by 1 year after testing.
Conclusions and Clinical Relevance: Without management changes designed to reduce the farm-level prevalence of MAP infection, paratuberculosis will continue to reduce farm income by decreasing milk production and potentially increasing premature removal from the herd.