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Title: Environmental sampling to predict fecal prevalence of Salmonella in an intensively monitored dairy herd

Author
item Van Kessel, Jo Ann
item Karns, Jeffrey
item WOLFGANG, D - PENN STATE UNIVERSITY
item HOVINGH, E - PENN STATE UNIVERSITY
item JAYARAO, B - PENN STATE UNIVERSITY
item Van Tassell, Curtis - Curt
item SCHUKKEN, Y - CORNELL UNIVERSITY

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2008
Publication Date: 10/1/2008
Citation: Van Kessel, J.S., Karns, J.S., Wolfgang, D.R., Hovingh, E., Jayarao, B.M., Van Tassell, C.P., Schukken, Y.H. 2008. Environmental sampling to predict fecal prevalence of Salmonella in an intensively monitored dairy herd. Journal of Food Protection. 71(10):1967-1973.

Interpretive Summary: Dairy cattle are known reservoirs for salmonellae but often the cattle that are harboring Salmonella don’t show any signs of illness. A dairy herd that was experiencing an outbreak of Salmonella enterica subsp. enterica Cerro was monitored for two years. Fecal samples from the lactating cows were collected every six to eight weeks and tested for the presence of Salmonella. The number of cows infected with Salmonella fluctuated between 8% and 88% throughout the observation period. During this sampling period, manure composites, bulk milk, and milk filters were cultured for the presence of Salmonella on a weekly basis. At least 60% of the manure composites were positive at each sampling. Salmonella was detected in 11% of milk samples and in 66% of the milk filters. Results of weekly bulk milk quality testing that are typically done to detect mastitic organisms and to monitor milk quality were typically well within acceptable ranges and had low relationship with the number of Salmonella-positive cows in the herd. The recovery of Salmonella from the milk filter closely paralleled the number of animals that tested positive for Salmonella. The milk filter is designed to remove any large particles from the milk when it is being pumped into the collection tank. Analysis of in-line milk filters has been used previously as a useful way to detect the presence of zoonotic bacteria in the milk. Based on results of this study, milk filter analysis may also be a convenient method for monitoring how many cows in the herd are harboring Salmonella and is a more sensitive measure of Salmonella, and perhaps other pathogens, in raw milk.

Technical Abstract: Although dairy cattle are known reservoirs for salmonellae, cattle that are shedding this organism are often asymptomatic and difficult to identify. A dairy herd that was experiencing an outbreak of Salmonella enterica subsp. enterica Cerro was monitored for two years. Fecal samples from the lactating cows were collected every six to eight weeks and tested for the presence of Salmonella using traditional culture methods. Fecal shedding of Salmonella fluctuated throughout the observation period and prevalence ranged from 8% to 88%. During this sampling period, manure composites, bulk milk, and milk filters were cultured for the presence of Salmonella on a weekly basis. At least 60% of the manure composites were positive at each sampling. Salmonella was detected in 11% of milk samples and in 66% of the milk filters. Results of weekly bulk milk quality testing (i.e. bulk tank somatic cell score, standard plate count, preliminary incubation count) were typically well within acceptable ranges and had low correlations with herd Salmonella prevalence. When observed over time, the recovery of Salmonella from the milk filter closely paralleled fecal prevalence of Salmonella in the herd. Analysis of in-line milk filters has been used previously as a useful way to detect the presence of zoonotic bacteria entering the bulk tank. Based on results of this study, milk filter analysis may also be a convenient method for monitoring shedding prevalence at the herd level and is a more sensitive measure of Salmonella, and perhaps other pathogens, in raw milk.