The Effect of Subclinical Mycobacterium paratuberculosis Infection on Milk Production in Michigan Dairy Cows

Abstract

The objective of this study was to determine the effect of subclinical Mycobacterium paratuberculosis infection on mature equivalent milk, protein, and fat production in a sample of Michigan dairy herds with a history of cows positive for M. paratuberculosis diagnosed by fecal culture. A prospective two-group cohort study was conducted. Participating herds were tested, and productivity and reproduction records were monitored for 18 mo. All cows aged 24 mo and greater were tested for M. paratuberculosis infection using the ELISA and radiometric fecal culture (RFC) techniques. Using both tests in parallel, the overall sample apparent prevalence for M. paratuberculosis infection was 41.8%. Adjusting for diagnostic sensitivity and specificity resulted in a calculated sample true prevalence of 59.9%. Subclinical paratuberculosis test-positive status had no statistically significant effect on mature equivalent milk, fat, or protein production. The results of this study concur with the findings of other studies, reporting that the magnitude and direction of the association between subclinical paratuberculosis infection and milk production depends upon the parity of the animal, stage of disease, and the stage in lactation being monitored. Assessment of the impact of subclinical paratuberculosis on milk production must consider the average parity of the sample population. In herds that have an average parity of 2 or less, subclinical paratuberculosis infection may have little impact on milk production.

Economic impact of paratuberculosis in dairy cattle herds: a review

“…On the other hand, Johnson et al (2001) assumed that the key to the inconsistent results presented in the literature regarding subclinical MAP-infection and milk production might not be in the method of diagnosis but in the parity of the cows in the study.…”

“…The studies of Johnson et al (2001) and Lombard et al (2005) did not show significant differences in milk fat and protein content between MAP-positive cows and their negative herdmates. In contrast Sweeney et al (1994) published that daily milk fat and milk protein production were significantly less for the infected cows.…”

“…The loss of genetic value of animals through premature culling (Johnson et al, 2001) and through trading restrictions is one of less evident losses. Opportunities to sell animals with a high genetic value from infected herds are limited (Kennedy and Benedictus, 2001).…”

“…Increasing the herd prevalence of PTB positive animals may result in greater longterm economic losses (Hutchinson, 1996;Johnson et al, 2001). …”

Use of Age and Milk Production Data to Improve the Ability of Enzyme-Linked Immunosorbent Assay Test Results to PredictMycobacterium Aviumssp.ParatuberculosisFecal Culture Status

“…Some studies have found that milk production is significantly decreased in subclinically infected animals as identified by fecal culture or serum ELISA testing, 1,18 whereas others have failed to find a significant difference between test-positive and -negative cattle with either type of test. 12 In the current study, cows that had a low 305 ME relative to other cows in the same herd had Figure 2. ROC curves based on predicted probabilities from the final (full) multivariable logistic regression model (with herd, quarter of the study year, age, herd-standardized 305-day ME milk production, and ELISA S/P ratio as predictors of fecal culture status) and a reduced model that did not include age and milk production as predictors.…”