Animal & Veterinary
USE OF POULTRY LITTER OR MANURE AS A FERTILIZER FOR CROPLANDS: IMPACT ON ANIMAL AND PUBLIC HEALTH
FDA Veterinarian Newsletter May/June 2000 Volume XV, No III
By H. E. Ekperigin, D.V.M., M.P.V.M., Ph.D.
This information was presented on March 1, 2000, at the departmental/graduate program seminar of the Virginia-Maryland Regional College of Veterinary Medicine, Maryland Campus, University of Maryland, College Park, Maryland.
Foodborne Diseases and Animal and Public Health
Foodborne illnesses occur worldwide. They can be caused by microbes like Salmonella or by chemical substances like mycotoxins. Salmonella are enteric bacteria that cause a significant proportion of foodborne illnesses. There are over 2,000 serologically distinct types (serotypes) of Salmonella. Expressions of the illnesses caused by Salmonella range from mild to severe diarrhea to anorexia, fever, nervous and respiratory signs, abortion, depression, shock, and death.
Mycotoxins are toxic secondary metabolites produced by fungi. They can be quite toxic to susceptible human beings and animals ingesting the mycotoxins. Expressions of toxicity in affected individuals can range from death to skin lesions or signs and symptoms of hepatotoxicity, nephrotoxicity, neurotoxicity, or genotoxicity. Mycotoxins are also carcinogenic, mutagenic, or teratogenic and can have adverse effects on the immune system. There are more than 300 known mycotoxins, and a large proportion of the world’s cereal grains is estimated to be contaminated with one or more mycotoxins.
Thus, foodborne illnesses can have severe negative impacts on human and animal health, and be fatal. The resultant economic losses can be quite significant. In the United States (U.S.), 76 million cases of foodborne illnesses are estimated to occur annually, and to result in 325,000 hospitalizations and 5,000 deaths. Economic losses due to medical expenses, lost production, and loss of life have been estimated to be as much as $35 billion. Such statistics can generate a lot of interest, attention, and concern as indicated in recent years in the U.S. by the relatively large number of reports of food-borne illnesses in the news media, and the initiation of major programs by government agencies to combat the problem.
CVM’s Role in Food Safety
One important way in which CVM contributes to human food safety is by working to ensure that feeds consumed by or intended for consumption by animals are safe for the animals, and do not pose a hazard to human health. CVM’s statutory responsibilities in this area include oversight over food additives and other substances that are added to feeds for one purpose or the other.
Feeds can be important sources of pathogenic microbes, microbial toxins, and toxic chemicals for food animals. Food animals, in turn, can be a source of microbial infections and toxicants for humans. Several recent examples have demonstrated the potential for contaminated feeds to have a severe negative impact on animal and human health, and the economy. One recent example is an outbreak of human Salmonellosis in Canada that was linked to Salmonella present in pig ear chews and other pet snacks. Another is an outbreak of aflatoxicosis in Texas that resulted in the death of about 30 dogs and was attributed to the inclusion of moldy corn in foods consumed by the dogs. In another well-known example, outbreaks of animal and human encephalopathies in Britain were linked to the consumption of rendered ruminant protein by cattle and the subsequent consumption by humans of food products from these cattle. A more recent incident involved the occurrence, in Belgium, of dioxin toxicosis in chickens and other food-producing animals ingesting dioxin-contaminated feed. The cost to the Belgian economy has been estimated at more than $750 million.
Thus, while feeds primarily serve as sources of nutrients for animals, they can also be important vehicles for transmission of foodborne illnesses to animals and humans.
CVM recently conducted nationwide surveys of feed ingredients to determine the extent of their contamination by Salmonella. The results indicate that the levels of contamination are fairly high for all feeds, and unexpectedly high for feeds of plant origin. When considered along with the recent spate of reports of outbreaks of human Salmonellosis and E. coli infections that were linked to the consumption of contaminated vegetables (lettuce, cantaloupe, radish, clover sprouts, and alfalfa sprouts), these results indicate that contamination of vegetables or feeds of plant origin by enteric pathogens probably occurs through routes other than the commonly speculated route of casual, incidental contact by handlers, etc.
Several million tons of poultry litter or manure are generated annually by poultry farms. A substantial proportion of the litter or manure is estimated to be disposed of by spreading on croplands. Salmonella and E. coli have been recovered from litter or manure for up to 120 days after the removal of poultry flocks that were raised on the litter, or produced the manure. Salmonella and E. coli have also been shown to survive in litter or manure-treated soils for up to 2 months. The results of our own preliminary studies show that Salmonella and E. coli can survive in litter or manure-treated soils for up to 90 days - a time frame that can comfortably accommodate the life span of many crops.
Based on the foregoing, we developed the hypothesis that the use of poultry litter or manure as a fertilizer for croplands can cause crops grown on such litter/manure-treated lands to become contaminated with Salmonella, and proposed research to test the hypothesis. The research basically will consist of experiments designed to isolate Salmonella and E.coli from litter/manure, litter/manure-treated soils, and crops grown on litter/manure-treated soils. The genetic relationships between various isolates will then be determined.
The United States Department of Agriculture has approved a proposal for funding a three-year study to conduct research on this hypothesis. A multi-disciplinary team of four scientists, including the author, and Drs. Morant, Nagaraja, and Oscar will implement the research. Dr. Mervalin Morant, the Co-Principal Investigator is an Associate Professor of Plant Pathology at the University of Maryland Eastern Shore. Her research interests include using poultry litter/manure to control plant nematodes.
Dr. Kakambi Nagaraja is a Professor of Veterinary Medicine at the University of Minnesota. His research interests and expertise include the genetic "finger-printing" of enteric pathogens.
Dr. Tom Oscar heads USDA’s Center of Excellence for Poultry Food Safety Research, at the University of Maryland Eastern Shore. His expertise includes risk assessment, and the development and use of computer simulations.
The grant allows for the hiring of a post-doctoral research fellow who will be responsible for the day-to-day implementation of the research.
In summary, foodborne illnesses can have a severe impact on animal and public health. Food animals are a source of microbial infections and toxicants for humans, and feeds can be important sources of pathogenic microbes, microbial toxins, and toxic chemicals for food animals.
FDA’s Center for Veterinary Medicine contributes to human food safety in one important way, among others, by working to ensure that feeds consumed by or intended for consumption by animals are safe for the animals, and do not pose a hazard to human health.
The discovery of a relatively high level of contamination of feeds of plant origin by Salmonella, and reports of contaminated vegetables causing human Salmonellosis and E. coli infections, indicate the possible existence of significant gaps in our knowledge of the epidemiology of foodborne illnesses. Research was proposed to close some of those gaps in knowledge by investigating whether pathogens shed in poultry manure can be transferred to crops (foods and feeds) grown on lands fertilized with the manure. The United States Department of Agriculture has approved the proposal, and will fund a three-year study.
References available upon request from the FDA Veterinarian.