Progress 01/27/16 to 09/30/16
Outputs
Target Audience:This study targeted farms using rotational grazing (i.e., sheep) to improve the soil fertility. One commerical farm that represent mixed crop-livestock farms in Northern California was enrolled during the spring-summer 2016 harvest season. Changes/Problems:Based on findings from 2015-2016 a pilot study conducted in a bio-diverse farm in the Central Valley that practice rotational grazing in fields that planted with covered crops (e.g., leafy greens, tomatoes, melons) a high variability of generic E. coli during monthly sampling was observed. Therefore, the number of farms was reduced (one commercial farm and one experimental-research farm) and the following changes were made to the initial study design: 1) increased of total soil samples, 2) increased of sampling frequency; 3) extended sampling period per farm. Moreover we will conduct a field trial to determine the baseline prevalence of STEC in a sheep flock using for rotational grazing and longitudinally test soil samples for generic E. coli concentration and presence/absence of pathogens (STEC and Listeria monocytogenes) from the time the animals are removed through harvest. The field trial will be conducted in an experimental -research farm at UC Davis, using the same sheep stocking density, management and planting practices as the farm in our observational study (commercial farm). What opportunities for training and professional development has the project provided?This project supoorted the training and academic development of an Undergraduate student and of a PhD student (partially). How have the results been disseminated to communities of interest?The results were reported to the participanting farm. What do you plan to do during the next reporting period to accomplish the goals?The association between possible predictor variables, including: grazing density, total grazing days, temperature, moisture level (data collected) and E. coli persistence and STEC will be evaluate by using generalized linear models.
Impacts
What was accomplished under these goals?
A time-series cross-sectional study (April 2016 to September 2016) was conducted in a small to medium-sized farm in Central California. The objectives 1 and 2 were completed in this farm. The persistence of microbial indicators (e.g., generic E. coli, and total coliforms) in the soil, produce, water and compost was evaluated. The prevalence of Shiga toxin-producing Escherichia coli (STEC) in the sheep and persistence in the soil was estimated. Composite soil samples were collected during 12 sampling visits (weekly in the first month and montly after). A total of 513 samples (432 soil, 22 fecal samples, 52 tomatoes, 4 water, 2 fertilizer and 1 compost sample) were collected and analized for generic E. coli and total coliforms (except fecal samples) and STEC. Fourteen percent (76/513) of the samples were STEC positive, none tested positive for E. coli O157:H7.
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Progress 01/27/16 to 09/30/16
Outputs
Target Audience:The target audience includes various farmers and extension educators (farm advisors) using rotational grazing (i.e., sheep) to improve the soil fertility. They were reached as part of the participation in the study, attending workshops and field-trips. This study is also important in defining research-based waiting periods between grazing and to harvest, which could inform FDA guidance for growers under the Produce Safety Rule related to Domesticated Animals and Wildlife. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?The project provided support for graduate research, thus helping to build capacity for future professionals in epidemiology and food safety. Drs. Jay-Russell and Pires mentored Laura Patterson, PhD student in Epidemiology Graduate Group at UC Davis. Patterson conducted the field work, sample collection, managed the data, conducted statistical analysis and will prepare the manuscript. How have the results been disseminated to communities of interest?The results have been disseminated through outreach activities involving farmers, extension specialists and farm advisor, working in diversified farms. They were reached as part of the workshops, field days and informal education activities (one to one meetings). What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Mixed crop-livestock farms (i.e., diversified farms) are those that raise a combination of livestock and vegetables and use these animals to graze crop residues or cover crops. These systems are considered sustainable because they utilize grazing to enhance soil fertility, recycle farm nutrients and provide another source of revenue through meat and fiber production. Potential food safety risks that may be associated with these bio-diversified farms, related to the interface of animals and crops, are unknown. Organic farmers report using the National Organic Program (NOP) standards for raw animal manure as a wait period following grazing, which require a 90 or 120 day interval between incorporating raw manure into the soil and harvest. To evaluate potential food safety risks from this practice, we conducted a repeated cross-sectional study of the persistence of generic E. coli and STEC in the soil and potential transfer to tomatoes. During the 2016 growing season, soil samples were collected from a certified organic farm following grazing of sheep on cover crop. In each visit, 36 soil samples were collected (432 total soil samples) from 3 fields (2 grazed fields and one non-grazed). Fecal samples were collected while the sheep were grazing in 2 fields. Tomato samples were collected at maturity. All samples (feces, soil, tomatoes) were processed within 24 hours by the Western Center for Food Safety (Jay-Russell Lab). Generic E. colifrom soil and tomatoes was enumerated by Most Probable Number (MPN). Also, each sample (soil, tomato, feces) was analyzed for the presence of O157 and non-O157 Shiga-toxin producingE. coli(STEC). In soil samples, genericE. coliwas present in 389 (n=432) with a concentration range of 0.09-4.2×105MPN/g. Non-O157 STEC was isolated from 13.2% (57/432) of the soil samples.In fecal samples, non-O157 STEC was isolated from 87.5% (14/16) of the samples. In tomato samples (harvested after day 90 until day 146), genericE. coliwas isolated from 3.8% (2/52) of samples and no pathogenicE. coliwas isolated from the samples. This study is important in defining research-based waiting periods between grazing and harvest inform best practices for both farmers and food safety regulators. This project will provide farmers with information about on-farm food safety, which will protect the economic viability and livelihood of diversified farms integrating crops and livestock.
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