Open Access Research article

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

Casey L Cazer1*, Rebecca M Mitchell2, Kellie M Cicconi-Hogan2, Michael Gamroth3, Roxann M Richert4, Pamela L Ruegg4 and Ynte H Schukken2

Author Affiliations

1 College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA

2 Department of Population Medicine and Diagnostic Sciences, Cornell University College of Veterinary Medicine, Animal Health Diagnostic Center, Ithaca, NY 14853, USA

3 Department of Animal and Range Sciences, Oregon State University, Corvallis, OR 97331, USA

4 Department of Dairy Science, University of WI, Madison, WI 53706, USA

For all author emails, please log on.

BMC Veterinary Research 2013, 9:234  doi:10.1186/1746-6148-9-234

Published: 27 November 2013

Abstract

Background

The 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.

Results

Results 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.

Conclusions

The 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.

Keywords:
Cattle; Mycobacteirum avium subsp. paratuberculosis; Antibodies; Bulk-tank milk; ELISA