Associations between Mycobacterium avium subsp. paratuberculosis antibodies in bulk tank milk, season of sampling and protocols for managing infected cows

Abstract

BackgroundThe objective of this study was to identify associations between the concentration of Mycobacterium avium subsp. paratuberculosis (MAP) antibodies in bulk milk and potential risk factors in herd management and herd characteristics, explaining high MAP antibody titers in milk. An extensive questionnaire was administered to 292 organic and conventional dairy farms from New York, Wisconsin and Oregon. Bulk milk samples were taken from each farm for MAP enzyme-linked immunosorbent assay (ELISA). A general linear model was constructed with MAP ELISA value as the outcome variable and the management factors and herd characteristics as independent variables, while at the same time controlling for the study design variables of state, herd size, and production system (organic or conventional). High bulk tank MAP ELISA value may be due to either a high prevalence of MAP in a herd with many cows contributing to the antibody titer or due to a few infected cows that produce large quantities of antibodies.ResultsResults of the regression models indicated that bulk milk ELISA value was associated with season of sampling and the presence or absence of protocols for managing MAP-positive cows. The concentration of MAP antibodies in bulk milk varied seasonally with a peak in the summer and low concentrations in the winter months. When compared to farms that had never observed clinical Johne’s disease, keeping MAP-positive cows or only culling them after a period of delay was associated with an increase in optical density.ConclusionsThe seasonal variation in MAP antibody titers, with a peak in the summer, may be due to a seasonal increase in MAP-bacterial load. Additionally, seasonal calving practices may contribute to seasonal fluctuations in MAP antibody titers in bulk tank milk. Keeping MAP-positive cows increases the antibody titer in bulk milk, likely due to direct antibody production in the infected cow and indirect triggering of antibody production in herdmates.

Identification of Mycobacterium avium subsp. paratuberculosis (MAP) in Sheep Milk, a Zoonotic Problem

“…This finding is in accordance with the results of another study about the association of season of sampling with change of MAP antibody titers in BTM. This study also confirmed that the MAP antibody titer follows a seasonal pattern in milk samples: peaking in the summer and drastically dropping in the winter [ 23 ].…”

“…On the other hand, the enzyme-linked immunosorbent assay (ELISA) is commonly used to assess the presence of sera antibodies directed against MAP in infected animal serum [ 10 ]. Although some studies have demonstrated that MAP-infected animals develop titers of antibodies against MAP in milk as well as sera [ 23 , 24 ], some studies believe that milk and serum ELISA act imprecisely before the clinical stage of JD [ 11 , 14 ].…”

A screening sampling plan to detect Mycobacterium avium subspecies paratuberculosis-positive dairy herds

“…The positivity to BTM ELISA examination was previously correlated with a ≥5% within-herd AP (Arrigoni et al, 2007;Lavers et al, 2014); recently, a correlation between results of repeated tests of bulk tank milk by ELISA and within-herd antibody prevalence was shown by Nielsen and Toft (2014) and, in our study, the correlation between within-herd AP and S/P value was confirmed. This finding is reasonable given that the ELISA tests performed on BTM and individual milk samples have the same target, and that, in herds with a high MAP prevalence of infection, several cows contribute to the antibody titer of BTM (Cazer et al, 2013). This finding may have significant application because it could allow a predictive estimation of the within-herd AP and consequently define priorities for control programs designed to reduce the prevalence of MAP-positive animals.…”

“…The correlation between BTM ELISA results and within-herd AP detected by individual milk sample analysis by ELISA must be interpreted with caution given that, in our study, the within-herd AP was estimated by a single sampling of all lactating cows and thus does not consider the variability due to the lactation stage of individual milk samples (Nielsen and Toft, 2012). Moreover, seasonal variation of MAP antibodies titers in BTM has been reported and related to a higher bacterial load or to seasonal calving practices (Cazer et al, 2013). Considering that the synchronization of calving is not a common practice in Italy and that the 2 BTM samplings were performed 6 mo apart, the misidentification of SSP MAP-positive herds by BTM examination, due to seasonal variations, was less likely to occur.…”

Longitudinal Study of Mycobacterium avium Subsp. paratuberculosis Antibody Kinetics in Dairy Cattle Using Sera and Milk throughout the Lactation Period

“…Strong agreement was observed between serum and milk when the antibody titer was high (>200). A high antibody titer is produced during the terminal stage of Johne’s disease, resulting in depression of the immune function and cows are being unable to control the disease [ 31 ]. Whereas in animals with a low (<100) MAP antibody titer, a weak agreement was observed in this study ( Figure 3 ) because this condition typically occurs only during the initial stages of the disease, when the immune system of the cow is able to control the bacterial infection.…”