Comparison of Individual, Pooled, and Composite Fecal Sampling Methods for Detection of Salmonella on U.S. Dairy Operations

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 serovar(s). During the U.S. Department of Agriculture National Animal Health Monitoring System Dairy 2007 study, data and samples were collected from dairy operations in 17 major dairy states. As part of the study, composite fecal samples (six per operation) were collected from cow areas, such as holding pens, alleyways, and lagoons, where manure accumulates. Fecal samples also were collected from individual cows (35 per operation), and fecal sample pools were created by combining samples from 5 cows (7 per 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 for which all three sample types were obtained, 41.4% (48 operations) were Salmonella culture positive based on individual samples, 39.7% (46 operations) were positive based on pooled samples, and 49.1% (57 operations) were positive based on 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 of 116), Salmonella was cultured from all three fecal sample types (individual, pooled, and composite), and 20 (51.3%) of these operations had exactly the same serovar in all three sample types. Use of composite fecal samples is less costly and time-consuming than use of individual or pooled samples and provides similar results for detecting the presence and identifying serovars of Salmonella in dairy herds. Therefore, composite sampling may be an appropriate alternative to culture of individual samples when assessing Salmonella status in dairy herds.

Epidemiology ofSalmonellasp. in California cull dairy cattle: prevalence of fecal shedding and diagnostic accuracy of pooled enriched broth culture of fecal samples

“…A higher prevalence in summer months may be related to heat stress, although such an association may be confounded by cow and management related factors such as increased water/moisture in environment due to feed bunk sprinkler use to mitigate heat stress (Edrington et al, 2009). Nevertheless, the higher prevalence of Salmonella shedding in the summer is in agreement with the previous studies that showed an increased prevalence in the summer months (Wells et al, 2001; Blau et al, 2005; Lombard et al, 2012). However, none of these three studies sampled cows throughout the entire year as was done in the current study.…”

“…The additional sampling of large dairies during the summer months may have biased the results to show a higher prevalence among the larger herds. Using a similar sampling scheme and data from the NAHMS 2007 study conducted between February and August 2007, Lombard et al (2012) reported an overall fecal Salmonella prevalence in individual cows of 14% in dairies across the U.S., with a prevalence of 3.9% in the West region of the U.S. While this prevalence in the West region is similar to that reported in the current study, the lack of random sampling in the Lombard et al (2012) study may have biased their results.…”

“…Using a similar sampling scheme and data from the NAHMS 2007 study conducted between February and August 2007, Lombard et al (2012) reported an overall fecal Salmonella prevalence in individual cows of 14% in dairies across the U.S., with a prevalence of 3.9% in the West region of the U.S. While this prevalence in the West region is similar to that reported in the current study, the lack of random sampling in the Lombard et al (2012) study may have biased their results. Blau et al (2005) used data from the NAHMS 2002 study, which included samples from milk cows over two years of age between March and September 2002, and reported a fecal Salmonella prevalence of 7.3% in dairies across the U.S. Possible reasons for the decreased prevalence of Salmonella in the current study, compared to previous reports, include use of a convenience sample of herds, differences in geographic regions and weather patterns at the time of sampling, differences in management practices between the study herds and differences in culturing methods used between the studies.…”

Salmonella in Dairy Cattle

“…In a study comparing individual, pooled, and composite fecal samples, it was found that composite fecal sampling was more sensitive at the sample level than the other 2 methods, primarily because of the increased number of cattle sampled indirectly through this method. 29 Hence, if one is merely trying to obtain a yes or no answer or identify and track specific serovars, or antimicrobial susceptibility patterns over time, composite fecal samples are typically collected from areas on dairy operations where manure accumulates from a majority of adult animals, such as holding pens, alleyways, and lagoons. 29 Newer techniques for diagnosing Salmonella are based on detection of genetic material from the bacteria, that is, polymerase chain reaction (PCR) techniques.…”

Herd- and individual-level prevalences of and risk factors for Salmonella spp. fecal shedding in dairy farms in Al-Dhulail Valley, Jordan

“…The prevalence of Salmonella infections associated with calf diarrhea could reach 18.7-43.5 % and that in calves showing no diarrhea could reach 27.7 % (Moussa et al 2010;Youssef and El-Haig 2012). Salmonella infections in cattle have been reported worldwide (Carrique-Mas et al 2010;Lombard et al 2012;Cho and Yoon 2014). The most frequently isolated serotypes from cattle are Salmonella montevideo, Salmonella typhimurium, Salmonella dublin, Salmonella enteritidis, Salmonella anatum, Salmonella newport, Salmonella cerro, Salmonella kentucky, and Salmonella orion (Alam et al 2009;Brichta-Harhay et al 2011;Strawn et al 2014).…”