Salmonella Contamination and Antibiotic Resistance on Pastured Poultry and Conventional Poultry Farms

Project Overview

Project Type: On-Farm Research
Funds awarded in 2005: $9,542.00
Projected End Date: 12/31/2005
Region: Southern
State: North Carolina
Principal Investigator:
Cedarose Siemon
Independent Research Scientist


  • Animals: poultry


  • Animal Production: feed/forage, parasite control, grazing - continuous, free-range, manure management, pasture fertility, preventive practices, grazing - rotational
  • Education and Training: extension
  • Pest Management: biological control, cultural control, genetic resistance, prevention
  • Sustainable Communities: new business opportunities

    Proposal abstract:


    Consumers are concerned about Salmonella contamination on poultry farms. Poultry has been implicated as an important reservoir of Salmonella. There have been claims that the pasture-raised poultry have an increased probability of being contaminated with Salmonella, due to the birds being raised outdoors (Phelps 1991). However, many proponents of pasture poultry claim that pasture-raised poultry is nearly Salmonella-free. There is little relevant data showing whether pasture poultry farms have high or low levels of Salmonella contamination. The main goal in this research is to provide data concerning Salmonella contamination on pasture poultry farms in comparison to contamination levels found on conventional farms.
    The southeastern region of the United States is home to many conventional poultry farms, supplying much of the country with poultry. Conventional poultry farms use low-dose antibiotics in the feed, which can lead to the development of antibiotic resistance in bacteria, such as Salmonella, that live within the intestinal tract of the birds. The World Health Organization is urging farmers throughout the world to control, limit or eliminate low-dose antibiotic use in the feeds of food animals such as poultry because of the direct antibiotic-resistance development within the bacteria (WHO, 2004). Antibiotic resistant bacteria can be passed on to humans through the food chain, which results in an infection resistant to antibiotic treatment (Anderson et al. 2003). Salmonella is commonly widespread throughout the world and several serotypes of Salmonella often exhibit resistance to multiple antibiotic agents. Conventionally raised poultry may contribute to the growth and expansion of antibiotic resistance as there is a constant selective pressure due to low-level antibiotic use, as growth promoters.


    SIEMON, CEDAROSE. Warren Wilson College, North Carolina State University (DVM), and University of Wisconsin Madison (DVM). Salmonella contamination and antibiotic resistance on pasture poultry and conventional poultry farms

    Salmonella contamination on nine conventional and nine pasture poultry farms was measured. The data showed that either a farm had no Salmonella or more than 50% of the samples were contaminated with Salmonella, suggesting that Salmonella is widespread if present in a flock. Four of nine conventional farms were contaminated with Salmonella and two of nine pasture poultry farms were contaminated with Salmonella. The null hypothesis that Salmonella contamination is not dependent on farming type, was not rejected. No evidence was found showing pasture poultry farms were more likely to be contaminated with Salmonella than conventional farms. Each Salmonella isolate from each Salmonella positive sample was tested for antibiotic resistance to twelve antibiotics. One of ninety-one conventional poultry Salmonella-positive samples was found to have antibiotic resistance. Twenty-seven of forty-five pasture poultry Salmonella-positive samples had antibiotic resistance. Only four separate isolates were found to have antibiotic resistance. The results suggest that Salmonella contamination is not a serious problem on pasture poultry farms. Funding of the supplies for the isolation of Salmonella came primarily from Warren Wilson College and for the facilities came from University of Wisconsin (DVM). Funding and assistance for the antibiotic-resistance testing were provided by Dr. Wondwossen Gebreyes of the State University of North Carolina (DVM).

    Project objectives from proposal:

    The Objectives of this research:

    One goal of this research is to compare Salmonella contamination levels in pasture poultry farms and conventional poultry farms, to see if Salmonella is dependent on the farming type. Also, to provide some of the first data on Salmonella contamination on pasture poultry farms and where it stands when compare to contamination levels found with conventional farms.
    Another goal in this research is to look at variance in antibiotic resistance patterns. To compare antibiotic resistance patterns and levels between conventional and pasture poultry farms. Also, to compare the variety of resistance patterns in conventional farms and pasture poultry farms. As well as, look for a relationship between antibiotic resistance patterns and antibiotics used on the farm.

    Why have these objectives?

    I have completed a pilot research project on the issue of Salmonella contamination and antibiotic resistance on pasture and conventional poultry farms in Wisconsin. Thirty poultry fecal droppings from nine pasture poultry and nine conventional poultry farms were collected and screened for the presence of Salmonella. The results showed that four out of nine conventional farms (45%) were infected with Salmonella and two out of nine pasture poultry farms (22%) were infected with Salmonella. A contingency table was constructed and a Fisher’s Exact Test was performed. Salmonella contamination was found to not be dependent on the farming type (p = 0.6171 at 95% confidence).

    The results from my study in Wisconsin came as a surprise to my North Carolina State University collaborators because the preliminary findings from their studies of swine, farms that don’t use antibiotics have higher Salmonella contamination than the farms that do use antibiotics. Prompted by this observation, I was encouraged to apply for support to be able to include a wider geographical area in my study (extend my research to the southeast region) where I am currently located. By doing this I may be able to reach more valid and conclusive findings in the two production systems. By doing this research in the southeast a comparison with the findings in Wisconsin and a better understanding of the contamination of Salmonella on pasture poultry compared to conventional poultry could be established. I would also test each Salmonella isolate for antibiotic resistance to see if farms using antibiotics are contributing to the expansion of antibiotic resistance in Salmonella.

    The Salmonella contamination found from farm to farm is important for finding patterns in contamination over the pasture poultry industry within the southeast region, but also between the southeast region and Wisconsin. Comparing the Salmonella contamination in pasture and conventional poultry farms will reveal any major differences in Salmonella control. These comparisons may bring viable rebuttals to the face of pasture poultry. In addition to the study of Salmonella prevalence, it would be interesting to determine the antibiotic resistance of each Salmonella isolate. By measuring the antibiotic resistance in the Salmonella isolates from each farming type, analysis of antibiotic-free pasture poultry, would be expected to exhibit less resistance than conventional poultry. I would also like to look at what the extent of antibiotic resistance on these different farms is for a production that doesn’t employ the use of antibiotics. Pasture poultry could be a new way of raising poultry without the use of antibiotics, but still control Salmonella contamination levels as well as the farms that do use antibiotics. As an alternative to conventionally raised poultry, pasture raised poultry is an inexpensive and sustainable method: low start-up costs, low labor costs, increases soil N and other nutrients from bird droppings, pasture is allowed to rest for long periods of time before poultry return, a natural biological cycle with the soil, plants, and birds.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.