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

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.

Salmonella and other Enterobacteriaceae in dairy-cow feed ingredients: antimicrobial resistance in western Oregon.

Several studies have suggested an association between the use of antimicrobial agents in animal feeds and an increased risk that humans will contract resistant strains of bacteria such as Salmonella species, Escherichia coli, and other enteric isolates. The authors of this study evaluated whether animal feeds might serve as sources of antimicrobial-resistant bacteria, especially bacteria that are pathogenic to humans. From July through August 1998, samples of feed ingredients were collected from a total of 50 feed piles located on 12 dairy farms in western Oregon. From a subset of 10 piles, repeated samples were collected over time until each pile was depleted. Analysis of the samples indicated that 42.0 percent of all 50 piles and 60.0 percent of the piles from which there was repeated sampling were presumptive positive for Salmonella. Sixty-two percent of 50 Enterobacteriaceae isolates showed ampicillin resistance, and 10.0 percent displayed tetracycline resistance. Other bacteria displayed varying degrees of resistance to ampicillin, streptomycin, tetracycline, or a combination of these antimicrobials. The extent of antimicrobial-resistant Enterobacteriaceae in feed ingredients observed in this study raises significant concerns about the potential for human health risks from food-producing animals such as dairy cows.