UC Davis

The increasing number of diversified small-scale farms (DSSF) and outdoor-raised livestock in California and nationwide, reflects growing consumer interest and demand for organic or sustainably-produced local foods, including humanely-raised animal products such as meat and eggs. However, there is a lack of research evaluating the unique agricultural management practices of DSSF and how these farming systems may involve risk factors that affect the transmission of foodborne pathogens in the food supply.Diversified farms are often small-scale and raise a combination of livestock and produce, or multiple livestock species with the intent of selling specialized animal products directly to consumers. However, livestock are reservoirs for foodborne pathogens like Shiga toxin-producing Escherichia coli (STEC). Additionally, raising pigs outside provides an opportunity for contact with feral pigs, which harbor zoonotic and foodborne pathogens. STEC remains one of the major causes of foodborne outbreaks in the US and STEC outbreaks associated with DSSF are most likely underreported The overall goal of this dissertation focused on evaluating the pre-harvest food safety risks on DSSF in California: Chapter 1 estimated the prevalence of STEC in cattle, goats, sheep and pigs raised on DSSF and evaluated risk factors associated with the prevalence of STEC using a multilevel logistic regression model. Chapter 2 used a species distribution modeling method Maximum Entropy (MaxEnt) to predict suitable habitat for feral pigs in California. Then the MaxEnt prediction map was overlapped with the location of over 300 outdoor-raised pig operations (OPO) in California to create a risk map, identifying areas most at risk for disease transmission between these two growing swine populations. In the past few decades, California has experienced an increase of feral pigs and a resurgence of outdoor-based domestic pigs and this trend has implications for pathogen transmission in the wildlife-livestock interface. The feral pig–outdoor-raised pig risk map built in Chapter 2 identified counties to target for a STEC prevalence study in Chapter 3. Fecal samples from both feral pigs and domestic pigs raised outdoors were collected in counties that had a higher risk for contact between feral pigs and domestic swine raised outdoors. The overall goal of Chapter 3 included assessing the prevalence of STEC in those counties as well as using a multilevel logistic regression model to assess risk factors associated with the presence of STEC in fecal samples. Although consumers perceive small-scale farms or outdoor-raised meat as safer or more natural, these three studies together demonstrated that livestock raised outdoors on small-scale farms are reservoirs for STEC and indicated the need for more studies to ascertain risk factors of foodborne pathogens on DSSF. As the number of DSSF farms continues to grow, evaluating risk factors and management practices that are unique to these small operations will help identify risk mitigation strategies and develop extension outreach materials to keep food safe from farm to fork and protect California’s agricultural economy.