Event Abstract

A preliminary spatial study to understand the distribution of feral pigs and outdoor-raised pigs in California

  • 1 University of California, Davis, United States
  • 2 Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, United States
  • 3 Center for Animal Disease Modeling and Surveillance, School of Veterinary Medicine, University of California, Davis, United States

Background and Objective Although most of America’s domestic swine production occurs inside confinement systems, the United States (U.S.) is currently experiencing a return to raising pigs outdoors, due to growing consumer demand for sustainably-produced local foods, including meat.1,2 However, raising swine outdoors creates an opportunity for disease transmission at the wildlife-livestock-human interface.3-7 Outdoor-raised pig operations are numerous and broadly distributed within most counties in California and California also has one of the largest and widest distributions of feral pigs. 8-10 Both domestic and feral pigs are reservoirs for zoonotic pathogens (e.g., Brucella suis, Salmonella spp. and Shiga toxin-producing Escherichia coli (STEC)).11-14 Expanding feral pig populations and increasing outdoor-raised swine operations, create a potential risk for increased disease exposure and transmission of emerging or reemerging zoonotic diseases, which could negatively impact public and swine health and the economic sustainability of California agriculture. 3,15,16 The objective of this preliminary spatial study is to understand the distribution and interface of feral pigs and outdoor-raised pigs, by identifying areas in California where domestic pig operations are within the average home range (i.e., habitat) of feral pigs. Brief Methods A list of outdoor-raised pig operations (OPO) in California was compiled between 2014-2019. Locations were identified through web-based searches and an IRB-approved online ArcGIS survey, which was announced to swine organizations through social media, newsletters, etc. and included questions regarding biosecurity practices, swine health, and feral pig presence. From the final compiled list of identified OPO, GPS coordinates were recorded using Google Earth Pro v7.3.2 and then added to a map of California using QGIS v3.6.17,18 Feral pig hunting tag coordinates were acquired from the California Department of Fish and Wildlife (CDFW) and used as a proxy for feral pig locations. Feral pig points were added to the California map of OPO. Then the Distance to Nearest Hub tool within QGIS was used to measure the distance between an outdoor-raised pig operation and the nearest feral pig tag location. Feral pig average home range is 3-5 miles2, depending upon various factors.19,20 Results A total of 47 ArcGIS surveys were completed between September 2, 2018 and November 12, 2018. Results indicated that 86.05% of the survey participants were swine owners and another 9.30% were pig managers. Excluding all non-answers in the following results, the total average outdoor-raised pig herd size was 24 with a range of 1-350 animals. The number of acres per operation ranged from 1-2,000 with a mean of 77.71 acres. Seventeen percent (7/41) of the responding participants had seen evidence of feral pigs on their operations, and a total of 37.5% (15/40) had seen feral pigs within 2-3 miles of their location, or within average feral home range. Of the 43 answers to the question regarding which county they raised pigs, the counties most represented in the survey were Sonoma (n=8), Lake (n=4) and San Luis Obispo and Yolo (n=3). CDFW provided 29,552 feral pig hunting tag GPS coordinates recorded between 1993-2010 from 53 counties. The map of identified California outdoor-raised pig operations contained 298 locations, found within 46 of California’s 58 counties. There was a final total of 45 counties with both outdoor-raised pig operations and feral pig hunting tags to analyze in this preliminary spatial study. Using the CDFW hunting tags as a proxy for feral pig habitat and the Distance to Nearest Hub tool in QGIS, approximately 46.98% (140/298) of the outdoor-raised pig operations were located within 3 miles2 of feral pig habitat and 55.70% (166/298) were within 5 miles2. Seven counties (Contra Costa, Monterey, San Benito, Santa Barbara, Santa Clara, Santa Cruz and Tehama) had 100% of outdoor-raised pig operations located within 3 miles2 of feral pig habitat. An additional three counties (Madera, Mariposa and San Mateo) had 100% of OPO located within 5 miles2 of feral pig habitat. Nine counties had 0% of outdoor-raised pig operations within 5 miles2 of feral pig habitat. The remaining 26 counties had a range of 9% to 91.67% of outdoor-based pig operations located within 5 miles2 of feral pig habitat. Limitations of this study include the source of swine locations. Outdoor-raised pig operations were skewed toward those located in the Bay Area and surrounding counties or that have an online presence. Hunting tags underestimate the actual distribution of feral pigs, because locations were only from areas accessible to hunters, like public land. Conclusion Since more than 45% of outdoor-raised pig operations identified in this preliminary spatial study were within the average home range of feral pigs, further study is warranted to investigate interactions of these two swine groups for disease transmission in the wildlife-livestock-human interface. The results of this project are significant because they will provide a foundation to design targeted, cost-effective disease surveillance programs for those counties at highest risk for disease transmission between feral and domestic pigs.


Thank you to all swine operations, county farm advisors and agency partners at USDA APHIS, USDA WS, CDFA, and CDFW for participating in my research and outreach seminars. This research is funded and supported by: • Agriculture and Food Research Initiative grant no. 2019-67011-29609 / project accession no. 1019249 from the USDA National Institute of Food and Agriculture • WCAHS and NIOSH grant #2U54OH007550


1. Salaheen S, Chowdhury N, Hanning I, Biswas D. Zoonotic bacterial pathogens and mixed crop-livestock farming. 2015 Poult Sci 001–13. 2015;94(1398-1410):peu055. doi:10.3382/ps/peu055 2. Honeyman MS, Pirog RS, Huber GH, Lammers PJ, Hermann JR. The United States pork niche market phenomenon. J Anim Sci. 2006;84(8):2269-2275. doi:10.2527/jas.2005-680 3. Hutton T, DeLiberto T, Owen S, Morrison B. Disease Risks Associated With Increasing Feral Swine Numbers and Distribution in the United States.; 2006. 4. Wyckoff a. C, Henke SE, Campbell T a., Hewitt DG, Vercauteren KC. Movement and habitat use of feral swine near domestic swine facilities. Wildl Soc Bull. 2012;36(1):130-138. doi:10.1002/wsb.96 5. Wyckoff a C, Henke SE, Campbell T a, Hewitt DG, VerCauteren KC. Feral swine contact with domestic swine: a serologic survey and assessment of potential for disease transmission. J Wildl Dis. 2009;45(2):422-429. doi:10.7589/0090-3558-45.2.422 6. Martinez-Lopez B, Alexandrov T, Mur L, Sanchez-Vizcaino F, Sanchez-Vizcaino JM. Evaluation of the spatial patterns and risk factors, including backyard pigs, for classical swine fever occurrence in Bulgaria using a Bayesian model. Geospat Health. 2014;8(2):489-501. doi:10.4081/gh.2014.38 7. Martínez-López B, Perez AM, Feliziani F, Rolesu S, Mur L, Sánchez-Vizcaíno JM. Evaluation of the risk factors contributing to the African Swine Fever occurrence in Sardinia, Italy. Front Microbiol. 2015;6(MAR):1-10. doi:10.3389/fmicb.2015.00314 8. Waithman JD, Sweitzer RA, VanVuren D, Drew JD, Brinkhaus AJ, Gardner IA. Range expansion; population sizes; and management of wild pigs in California. J Wildl Manage. 1999;63(1):298-308. doi:10.2307/3802513 9. Waithman JD. Guide To Hunting Wild Pigs in California. 2001;(August):3-41. 10. USDA-APHIS-VS-CEAH-NAHMS. Swine 2012: Reference of Management Practices on Small-Enterprise Swine Operations in the United States.; 2014. 11. Pires AFA, Funk J, Lim A, Bolin SR. Enumeration of Salmonella in feces of naturally infected pigs. Foodborne Pathog Dis. 2013. doi:10.1089/fpd.2013.1547. 12. Pires a F a, Funk J a, Bolin C. Risk factors associated with persistence of Salmonella shedding in finishing pigs. Prev Vet Med. 2014;116(1-2):120-128. doi:10.1016/j.prevetmed.2014.06.009 13. Tseng M, Fratamico PM, Bagi L, Manzinger D, Funk JA. Shiga toxin-producing E. coli (STEC) in swine: Prevalence over the finishing period and characteristics of the STEC isolates. Epidemiol Infect. 2015;143(3):505-514. doi:10.1017/S0950268814001095 14. Farzan A, Friendship RM, Cook A, Pollari F. Occurrence of Salmonella, Campylobacter, Yersinia enterocolitica, Escherichia coli O157 and Listeria monocytogenes in Swine. 2010;57:388-396. doi:10.1111/j.1863-2378.2009.01248.x 15. Hill DE, Dubey JP, Baroch JA, et al. Surveillance of feral swine for Trichinella spp. and Toxoplasma gondii in the USA and host-related factors associated with infection. Vet Parasitol. 2014;205(3-4):653-665. doi:10.1016/j.vetpar.2014.07.026 16. Glazier N. Swine Brucellosis Outbreak in New York. lancasterfarming.com. http://www.lancasterfarming.com/farming/dairy/swine-brucellosis-outbreak-in-new-york/article_d1b75a7e-a75f-5ab8-933a-b0df686aa82d.html. Published 2017. Accessed September 30, 2017. 17. QGIS Development Team (2019). QGIS Geographic Information System. Open Source Geospatial Foundation Project. http://qgis.osgeo.org 18. Google LLC. Google Earth Pro. 2019. http://www.earth.google.com. 19. Holmstrom L. Identifying and optimizing prevention and control strategies against the spread of viral pathogens within U.S. feral swine populations. 2013. 20. Jack Mayer. Feral Hog Behavior. extension. https://articles.extension.org:443/pages/64381/feral-hog-behavior. Published 2012.

Keywords: zoonotic disease surveillance, outdoor-raised swine, wildlife-livestock-human interface, sustainable agriculture and food safety, Feral pigs (Sus scrofa L.)

Conference: GeoVet 2019. Novel spatio-temporal approaches in the era of Big Data, Davis, United States, 8 Oct - 10 Oct, 2019.

Presentation Type: Student Poster-session

Topic: Spatial methods for environmental & exposure epidemiology and climate change

Citation: Patterson L, Belkhiria JA, Martínez-López B and Pires AF (2019). A preliminary spatial study to understand the distribution of feral pigs and outdoor-raised pigs in California. Front. Vet. Sci. Conference Abstract: GeoVet 2019. Novel spatio-temporal approaches in the era of Big Data. doi: 10.3389/conf.fvets.2019.05.00027

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Received: 20 Jun 2019; Published Online: 27 Sep 2019.

* Correspondence: Mx. Laura Patterson, University of California, Davis, Davis, United States, lpatters@ucdavis.edu