Buffers between grazing sheep and leafy crops augment food safety

Abstract

The presence of livestock in or near fresh-market vegetable fields has raised concerns about the potential for contaminating produce with pathogenic bacteria. To develop buffer zones for grazing near production of leafy greens, we assessed the prevalence of Escherichia coli O157:H7 and Salmonella species in sheep that were grazed on alfalfa fields during the winter in California's Imperial Valley. We found E. coli O157:H7 in 1.8% of fecal samples and 0.4% of soil samples, and Salmonella in 0.8% of fecal samples and 0.4% of soil samples. Our results indicate that sheep grazing on alfalfa in the Imperial Valley have a low prevalence of these pathogens in their feces and that these bacteria are rarely found in soil from fields with grazing sheep. The California Leafy Green Products Handler Marketing Agreement guideline of 30 feet between grazing lands or domestic animals and the crop edge is adequate to minimize potential contamination of nearby crops.

Persistence of Escherichia coli in the soil of an organic mixed crop‐livestock farm that integrates sheep grazing within vegetable fields

“…Mixed crop‐livestock farms (MCLF) integrate livestock and crop production using their animals to graze crop residues and/or cover crops before replanting fields to vegetable or fruit crops (Hilimire, ; Martin et al, ). These MCLF operations, that are generally small to medium sized, are considered sustainable because grazing and the manure deposited by livestock, enhances soil fertility, recycles farm nutrients and the livestock provide another source of revenue through meat or fibre production (Hilimire, ; Hoar et al, ; Martin et al, ; Salaheen, Chowdhury, Hanning, & Biswas, ). However, the United States Department of Agriculture (USDA), Food and Drug Administration (FDA) Food Safety Modernization Act (FSMA) Produce Safety Rule and third‐party food safety auditors have directed attention towards these mixed crop‐livestock farms, due to the possible risk of produce becoming contaminated by foodborne pathogens contained in livestock faeces (Park et al, ; United States Department of Agriculture Food and Drug Administration (FDA), ).…”

“…Mixed crop-livestock farms (MCLF) integrate livestock and crop production using their animals to graze crop residues and/or cover crops before replanting fields to vegetable or fruit crops (Hilimire, 2011;Martin et al, 2016). These MCLF operations, that are generally small to medium sized, are considered sustainable because grazing and the manure deposited by livestock, enhances soil fertility, recycles farm nutrients and the livestock provide another source of revenue through meat or fibre production (Hilimire, 2011;Hoar et al, 2013;Martin et al, 2016;Salaheen, Chowdhury, Hanning, & Biswas, 2015).…”

“…Sheep are asymptomatic reservoirs of STEC and faecal shedding from ruminants may increase during periods of stress (Cooley et al, 2013;Edrington et al, 2009;Moynihan, Richards, Ritz, Tyrrel, & Brennan, 2013;Ongeng et al, 2014;Schilling et al, 2012). Raw manure deposited in production fields by grazing animals may introduce enteric foodborne pathogens into the growing environment and lead to increased contamination of produce, especially those high-risk crops that grow in contact with the soil, which then may become vehicles for these pathogens in the food supply (Gorski et al, 2011;Hoar et al, 2013;Niemira & Zhang, 2014;Salaheen et al, 2015;Strawn, Fortes, et al, 2013). Mixed crop-livestock farmers, including smallto medium-sized growers, face increasing economic challenges.…”

Shiga toxin (stx) encoding genes in sheep and goats reared in Trinidad and Tobago

“…The absence or low prevalence of O157 serogroups and eae -positive isolates in stx positive small ruminant samples was also confirmed by Cortes et al (2005) who screened 105 different STEC serotypes recovered from goat feces, and reported the serogroups neither belonged to the O157 serogroup nor were they eae -positive [ 11 ]. Studies which have successfully identified O157 serogroup in sheep or goat feces report a prevalence of between 1.8–11.7% [ 25 , 52 – 55 ]. Pavez-Munoz et al (2021) also failed to recover any O157 isolates from sheep samples collected as part of a backyard production system surveillance [ 49 ].…”

Risk factors of Shiga toxin-producing Escherichia coli in livestock raised on diversified small-scale farms in California

“…integrated crop–livestock farms) by using their animals to graze crop residues or cover crops before planting a field with fresh produce [ 1 , 7 ]. Grazing improves soil fertility and provides farm owners with another source of revenue through fibre or meat products [ 1 , 8 ]. Additionally, many countries promote diversified farming systems as an alternative to intensive agriculture, displaying a willingness to transition to agroecology, in line with the UN Sustainable Development Goal number 12: ‘Ensure sustainable consumption and production patterns’ [ 9 ].…”