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Title: Comparison of individual, pooled, and composite fecal sampling methods for detection of Salmonella on U.S. dairy operations

Author
item LOMBARD, J - Animal And Plant Health Inspection Service (APHIS)
item BEAM, A - Animal And Plant Health Inspection Service (APHIS)
item NIFONG, E - Animal And Plant Health Inspection Service (APHIS)
item FOSSLER, C - Animal And Plant Health Inspection Service (APHIS)
item KOPRAL, C - Animal And Plant Health Inspection Service (APHIS)
item DARGATZ, D - Animal And Plant Health Inspection Service (APHIS)
item WAGNER, B - Animal And Plant Health Inspection Service (APHIS)
item ERDMAN, M - Animal And Plant Health Inspection Service (APHIS)
item Cray, Paula

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2012
Publication Date: 9/1/2012
Citation: Lombard, J.E., Beam, A.L., Nifong, E.M., Fossler, C.P., Kopral, C.A., Dargatz, D.A., Wagner, B.A., Erdman, M.M., Cray, P.J. 2012. Comparison of individual, pooled, and composite fecal sampling methods for detection of Salmonella on U.S. dairy operations. Journal of Food Protection. 75(9):1562-1571.

Interpretive Summary: Salmonella is an important food borne pathogen which can be transferred from contaminated foods to human resulting in gastroenteritis. It has been received from all food producing animals including dairy cattle. It is important to assess the prevalence of Salmonella in animals on farms in order to better understand how we might control for their presence prior to the bacteria entering the food supply. However, these studies are very expensive both from a manpower and laboratory standpoint. It is important for us to determine if there are more cost effective ways to test for the presence of Salmonella. We conducted a national study on dairy farms in the United States to determine if we could obtain the same information by collecting pooled or composite fecal samples for bacterial culture versus the typical testing of individual fecal samples for the presence of Salmonella. The USDA’s National Animal Health Monitoring System Dairy 2007 study collected data and samples on dairy operations from 17 major dairy states. As part of the study, composite fecal samples (6/operation) were collected from cow areas, such as holding pens, alleyways, and lagoons, on operations where manure accumulates. Fecal samples were also collected from individual cows (35/operation) and fecal sample pools were created by combining samples from 5 cows (7/operation). A total of 1,541 composite fecal samples were collected from 260 operations in 17 states, and 406 (26.3%) of these samples were culture positive for Salmonella. Among the 116 operations that collected all 3 sample types, 41.4% (n = 48) were Salmonella culture positive by individual samples, 39.7% (n = 46) by pooled samples, and 49.1% (n = 57) by composite fecal samples. Relative to individual samples, the sensitivity of composite fecal samples for determining herd infection status was 85.4% and the sensitivity of pooled fecal samples was 91.7%. On 33.6% of operations (39/116), Salmonella was cultured from all 3 sample types (individual, pooled, and composite fecal). Of these, 20 operations (51.3%) had exact Salmonella serotype matches in all 3 sample types. Composite fecal sampling is less costly and time consuming than individual or pooled sampling and provides similar results for detecting the presence and identifying serotypes of Salmonella in dairy herds. Therefore, it may be considered an alternative to culture of individual samples when assessing Salmonella status in dairy herds and results in significant manpower and cost savings. These data are important for the dairy industry and other researchers as they develop and implement prevalence studies.

Technical Abstract: The objectives of this study were to estimate the prevalence of Salmonella for individual, pooled, and composite fecal samples and to compare culture results from each sample type for determining herd Salmonella infection status and identifying Salmonella serotype(s). The USDA’s National Animal Health Monitoring System Dairy 2007 study collected data and samples on dairy operations from 17 major dairy states. As part of the study, composite fecal samples (6/operation) were collected from cow areas, such as holding pens, alleyways, and lagoons, on operations where manure accumulates. Fecal samples were also collected from individual cows (35/operation) and fecal sample pools were created by combining samples from 5 cows (7/operation). A total of 1,541 composite fecal samples were collected from 260 operations in 17 states, and 406 (26.3%) of these samples were culture positive for Salmonella. Among the 116 operations that collected all 3 sample types, 41.4% (n = 48) were Salmonella culture positive by individual samples, 39.7% (n = 46) by pooled samples, and 49.1% (n = 57) by composite fecal samples. Relative to individual samples, the sensitivity of composite fecal samples for determining herd infection status was 85.4% and the sensitivity of pooled fecal samples was 91.7%. On 33.6% of operations (39/116), Salmonella was cultured from all 3 sample types (individual, pooled, and composite fecal). Of these, 20 operations (51.3%) had exact serotype matches in all 3 sample types. Composite fecal sampling is less costly and time consuming than individual or pooled sampling and provides similar results for detecting the presence and identifying serotypes of Salmonella in dairy herds. Therefore, it may be considered an alternative to culture of individual samples when assessing Salmonella status in dairy herds.