Abstract
Stressful conditions in animal production facilities may exacerbate the fecal shedding and foodborne transmission of non-typhoidal Salmonella enterica subsp. enterica. Dairy cows are reservoirs of this zoonotic microorganism, and its prevalence has roughly doubled in the past decade on dairy farms in United States. Dairy cows are commonly overstocked at the feed bunk, and stressors placed on the animal prior to parturition may exacerbate Salmonella shedding. However, no studies have evaluated the impact of overstocking and metabolic stress on fecal concentrations of the pathogen. Therefore, we conducted a field trial with 120 multiparous dairy cows randomized into one of four treatment groups with different stocking densities at the feed bunk during the periparturient period as follows: US, understocked from −60 to −1 DRC; OS, overstocked from −60 to −1 DRC; USOS, understocked from −60 to −26 DRC/overstocked from −25 to −1 DRC; and OSUS, overstocked from −60 to −26 DRC/ understocked from −25 to −1 DRC. Fecal and blood samples were collected at four time points relative to calving. qPCR assays were used to quantify Salmonella invA gene and total bacterial community from fecal samples, and a subset of isolates recovered from fecal bacterial culture were characterized using pulsed field gel electrophoresis and serotyping. Serum non-esterified fatty acids (NEFA) were measured as a metabolic stress indicator using an immunoassay. Multivariable analyses were performed to test if changes in Salmonella concentrations were associated with stocking density, energy balance, or days relative to calving. From fecal isolates, three Salmonella serovars were identified, S. Cerro; Kentucky; Meleagridis. Concentrations of Salmonella increased as cows approached calving. Higher stocking densities at the feed bunk did not impact total bacterial community or NEFA; however, cows in the overstocked groups had higher Salmonella fecal concentrations. Further, cows with higher NEFA concentrations after calving had a higher likelihood of detection of Salmonella. Future farm interventions should aim to reduce environmental and metabolic stress during the periparturient period to decrease the dissemination of Salmonella to cattle, the environment, and humans.
Highlights
Non-typhoidal Salmonella enterica subsp. enterica is the most frequent cause of foodborne related-deaths and hospitalizations in the United States, and in the last few decades, most human outbreaks have been associated with antimicrobial resistant strains [1,2,3]
Taurine has been identified as an important regulator for the intestinal microbiota and short chain fatty acids (SCFAs) production [46], providing gut health by inhibiting pathogen growth. This is interesting and could be paradoxical since beneficial metabolites such as butyric, acetic, and lactic acid that could justify the increased microbial quantification at −15 Days relative to calving (DRC) could have an inhibitory effect on Salmonella proliferation [44], suggesting that others factors besides diet were involved on the observed microbial dynamics.A variety of serotypes have been described across a diverse compendium of sample types from cattle [47], many recovered from fecal samples of seemingly healthy animals and lymphatic tissues at abattoirs [31]
The longitudinal approach used in this study allowed for detection of changes in fecal concentrations of Salmonella during the periparturient period
Summary
Non-typhoidal Salmonella enterica subsp. enterica (from here referred as Salmonella) is the most frequent cause of foodborne related-deaths and hospitalizations in the United States, and in the last few decades, most human outbreaks have been associated with antimicrobial resistant strains [1,2,3]. Dairy cattle are reservoirs of Salmonella, and there have been strategies to decrease the prevalence of foodborne pathogens on-farm, the prevalence of Salmonella has roughly doubled in the past decades on dairy farms in United States [11, 12] This presents a threat to food safety, since cull dairy cows contribute significantly to the U.S beef supply, and environmental dissemination of Salmonella can result in contamination of other foods. This increase in prevalence may be attributed to pathogen-associated factors, such as the emergence of cattle-adapted strains Understanding the epidemiology of Salmonella in dairy cows is necessary to design interventions to decrease shedding at the farm level to protect human and animal health
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