No abstract

The paper was designed to assess the influence of Mycobacterium avium subsp. paratuberculosis (MAP) infection status of cows at culling (antibody positive vs negative) on carcass traits: weight and conformation and fat cover scores. A generalized least squares linear model was used to assess the influence of MAP on weight. Subsequently, a random effects logistic regression was completed in order to model the relation between MAP and conformation score (fair vs poor carcasses). A random effects ordered logistic model was used to estimate the influence on fat cover. The results indicated that seropositives had carcass weights 58. 45 (34.65-83.35) kg lower than seronegatives. Regarding conformation score, the odds of having poor conformation instead of fair was 3.85 (1.35-11.85) times higher in seropositives. The odds of seropositives achieving a higher fat cover was approximately 5 (1.41-9.09) times lower than the odds for seronegatives. The estimated effects could be useful when assessing the economic benefits of a paratuberculosis control program.Additional key words: Johne´s disease, carcass traits, serology, ELISA, economic losses.Correspondence should be addressed to Francisco J. Dieguez: franciscojavier.dieguez@usc.es

The objective of this study was to determine the correlation between the results obtained with the ELISA technique for antibodies to Mycobacterium avium ssp. paratuberculosis in serum and bulk tank milk at the herd level. For this purpose, 203 samples of bulk tank milk were analyzed with 2 commercial ELISA from dairy herds with a prevalence of seropositive animals that was also determined. In regard to the reference test (results in blood serum), the sensitivity of the bulk tank milk test to detect high-positive herds (≥10% seroprevalence) ranged from 85.7 to 71.4%. The specificity to detect herds with no seropositive animals ranged from 70.5 to 53%. In a quantitative approach, Pearson correlation coefficients, reported as a measure of the linear association between herd seroprevalences and transformed optical density values recorded in bulk tank milk, were 0.39 and 0.54 for the studied ELISA. Although the test results were relatively fairly correlated with the within-herd prevalence, the practical utility of bulk tank milk testing for Mycobacterium avium ssp. paratuberculosis seems limited, especially regarding specificity.