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

Project Overview

OS05-025
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

Commodities

  • Animals: poultry

Practices

  • 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

    Abstract:

    Antimicrobials have been used in low-dose amounts throughout the food animal production industry for over thirty years. The World Health Organization has identified several unfavorable consequences to the low-level, long-term exposure to antimicrobials that livestock undergo in commercial production systems (WHO 1997):
    • Increased prevalence of antimicrobial resistant bacteria in food animals, which can be transferred to humans through consumption
    • Resistance genes of bacteria in food animals can be transferred to human pathogens
    • Increased occurrence of infection by resistant pathogens
    • Possible loss of antimicrobial effectiveness for both animals and humans
    Salmonella is a widespread food-borne pathogen that causes gastrointestinal infection. An estimated 1.4 million people per year in the US are infected with Salmonella (Voetsch et al. 2004). Contaminated poultry is a common source that causes Salmonella infection in humans. On-farm control of Salmonella has been shown to directly decrease the level of contamination of poultry meat at retail (Wegener et al. 2003). Interestingly, Salmonella develop resistance quickly to antimicrobials and are perhaps the most widely studied bacteria for its severity in multi-drug resistance development.
    Pasture poultry farms are a new way of raising poultry intensively on the pasture and doesn’t employ the use of antimicrobials. Being a new form of raising poultry without antimicrobials, pasture poultry farms are of importance in the effort to raise poultry without increasing the antimicrobial resistant bacteria population. However, one main reason antimicrobials are used in commercial poultry farming is to control the on-farm levels of Salmonella prevalence, therefore, we must study Salmonella prevalence on pasture poultry farms to know if poultry can be raised without antimicrobials and not have significantly higher levels of Salmonella prevalence.

    There are two objectives to this study:
    1. To see if Salmonella prevalence is significantly different on pasture poultry farms than on commercial poultry farms.
    2. To see if antimicrobial resistance is different between the pasture and commercial poultry farms.
    This study was conducted in Wisconsin in 2004 and in North Carolina in 2005, a total of 17 pasture and 14 commercial farms were studied. From each farm thirty fecal samples were collected and analyzed for Salmonella contamination and antimicrobial resistance.
    Commercial and pasture poultry farms were found to not be significantly different in Salmonella contamination (p-value 0.4928). Samples collected from commercial farms were found to be 2.6 times more likely to be contaminated with Salmonella (<0.0001). In NC, significantly more Salmonella isolates from commercial farms were resistant to: amoxicillin/clavulanic acid (<0.005), ampicillin (<0.005), chloramphenicol (<0.005), streptomycin (<0.005), sulfisoxazole (<0.005), and tetracycline (<0.005). In NC, significantly more Salmonella isolates from pasture farms were resistant to (Graph 1.): ceftriaxone (<0.05) and cephalothin (<0.005). Multi-drug resistance (resistance to ?5 antimicrobials) within the Salmonella isolates was found to be 85 times more likely in commercial poultry farms than in pasture poultry farms (<0.0001).
    Pasture poultry farms didn’t use antimicrobials and wasn’t found to have a higher prevalence of Salmonella than the commercial farms. Multidrug resistance was only in NC and was in commercial farms exclusively. North Carolina had a great majority of the antimicrobial resistance. Why might pasture farms have any resistance? Resistant Salmonella could be transported onto the farm from the hatchery or the feed mill. Feed mills mill feed with low-dose antimicrobials in it for other farmers, feed mills could be an environment for antimicrobial resistant Salmonella to develop. Pasture poultry farming may be the way in which poultry can be raised without the use of antimicrobials and without the risk of higher Salmonella prevalence. However, more research is required to further verify these findings.

    Bibliography:

    World Health Organization-Emerging and other Communicable Diseases, Surveillance and Control. 1997. The Medical Impact of Antimicrobial Use in Food Animals. Berlin, Germany. 1-6

    Voetsch A.C., Van Gilder T.J., Angulo F.J. et al. 2004. Emerging Infections Program FoodNet Working Group. FoodNet estimate of the burden of illness caused by nontyphoidal Salmonella infections in the United States. Clinical Infectious Diseases 2004; 38 (Suppliment 3):S127-S134

    Wegener C., Hald T., Wong D., Madsen M., Korsgaard H., Bager F., Gerner-Smidt P. and Molbak K. 2003. Salmonella Control Programs in Denmark. Emerging Infectious Diseases. 9: 774-779

    Tables, figures or graphs mentioned in this report are on file in the Southern SARE office.

    Contact Sue Blum at 770-229-3350 or
    sueblum@southernsare.org for a hard copy.

    Introduction

    The World Health Organization has identified several unfavorable consequences to the low-level, long-term exposure to antimicrobials that livestock undergo in commercial production systems (WHO 1997): Increased prevalence of antimicrobial resistant bacteria in food animals, which can be transferred to humans through consumption; resistance genes of bacteria in food animals can be transferred to human pathogens; increased occurrence of infection by resistant pathogens; possible loss of antimicrobial effectiveness for both animals and humans. Commercial broiler farms typically implement low-dose feed-grade antimicrobials and have since the 1970’s.
    An estimate of 1.4 million cases of illness, 15,000 hospitalizations, and 400 deaths in the U.S. per year are due to Salmonella infection (Voetsch et al. 2004). There are several reasons why Salmonella prevalence ought to be studied on poultry farms. Firstly, Salmonella are widespread food-borne pathogens. Secondly, Salmonella develop resistance quickly and have been found to be resistant to a wide variety of antimicrobials. Thirdly, Salmonella is common in poultry and is spread to humans by contaminated meat. In Denmark, a multi-year, nationwide study showed that the level of Salmonella contamination on the farm affects the level at retail (Wegener et al. 2003). If the prevalence of Salmonella on the farm is high then the prevalence at retail may be high, therefore it is important to measure Salmonella prevalence at the farm level. Measuring Salmonella after slaughter does not directly show the prevalence of Salmonella for a particular farming system because the carcass may have become contaminated with Salmonella from the slaughter facilities.
    Generally, and for this study, no antimicrobials are used on the pasture poultry farms. On pasture poultry farms the broilers are raised in brooder houses until 3 weeks of age, then moved into small (around 10’x12’) pens on pasture. The pens have a roof (often a piece of tin), open air wiring for walls, and no flooring, giving the broilers direct access to the pasture. The pens are moved a minimum of once a day to a new area of pasture, which usually hadn’t had broilers on it in over a year. Pens have from 25 to 100 broilers inside and the broilers are slaughtered from 55-100 days old. On conventional farms the broilers are raised indoors in a large house for their entire life, an all-in-all-out system. Each batch of broilers enter the barn within a week of the last flock, often after the bedding on the floor has been mixed. Houses have from 15,000-75,000 broilers inside and the broilers are slaughtered from 40-55 days old. Feed grade antimicrobials were routinely used on the conventional farms.
    Pasture poultry farms have not been thoroughly tested for Salmonella prevalence. Processed chickens from free-range poultry have been tested for Salmonella prevalence (Bailey and Cosby 2005). However, it is difficult to say if Salmonella prevalence is a direct result of how the broilers are reared without testing Salmonella prevalence on the farm.

    Bibliography:

    World Health Organization-Emerging and other Communicable Diseases, Surveillance and Control. 1997. The Medical Impact of Antimicrobial Use in Food Animals. Berlin, Germany. 1-6

    Voetsch A.C., Van Gilder T.J., Angulo F.J. et al. 2004. Emerging Infections Program FoodNet Working Group. FoodNet estimate of the burden of illness caused by nontyphoidal Salmonella infections in the United States. Clinical Infectious Diseases 2004; 38 (Suppliment 3):S127-S134

    Wegener C., Hald T., Wong D., Madsen M., Korsgaard H., Bager F., Gerner-Smidt P. and Molbak K. 2003. Salmonella Control Programs in Denmark. Emerging Infectious Diseases. 9: 774-779

    Bailey, J.S. and Cosby D.E. 2005. Research note: Salmonella Prevalence in Free-Range and Certified Organic Chickens. Journal of Food Protection. 68: 2451-2453

    Project objectives:

    To compare pasture and commercial poultry farms in terms of:
    -Farm and sample level Salmonella prevalence
    -Antimicrobial resistance within the Salmonella found

    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.