POULTRY FACT SHEET NO. 30
COOPERATIVE EXTENSION, UNIVERSITY OF CALIFORNIA
Use of Competitive Exclusion Products for Poultry
University of California, Cooperative Extension
Joan S. Jeffrey, DVM, MS, ACPV, Extension Poultry Specialist
Competitive exclusion (CE) is a term that has been used to describe the protective effect of the natural or native bacterial flora of the intestine in limiting the colonization of some bacterial pathogens. There is a large body of scientific literature on this subject dating back over 25 years. Only in the last few years have these concepts been developed to the point that commercial preparations of CE products are available for use in poultry. Competitive exclusion products are also called probiotics, direct-fed microbials or CE cultures. For simplicity the term CE product will be used in this Fact Sheet. Competitive exclusion products may provide a significant tool for the poultry industry in combating the occurrence of intestinal disease and reduction of food borne pathogens.
Physiologic maturation of the intestine. The newly hatched chicken or turkey gut is devoid of bacteria. In the first few hours to days of life, the normal gut bacteria (microflora) that inhabit the intestine become established. This holds true in all animals. Intestinal microflora function to break down ingested food, produce some vitamins and most importantly provide a natural barrier to harmful bacteria that enter the host. In the days when chicks were hatched under a hen, the bacteria shed in the feces of the healthy adult hen provided the inoculum for the establishment of a similar microflora in the chicks. With the advent of modern incubation, the first bacteria the chick or poult is exposed to are those in the incubator, chick box, and litter of the poultry house.
Factors influencing the microflora of the gut once it is established. The normal microflora of the intestinal tract is made up of a diverse population of bacteria. Some of these bacteria are anaerobic (grow without oxygen), some are aerobic (oxygen dependent) and some are in between (facultative anaerobes or microaerophilic). All of these bacteria are in competition for survival. They compete for attachment sites and nutrients from the ingesta passing through the intestine. Each species of bacteria has specific requirements for growth. They are affected by relative acidity or alkalinity (pH) of their environment and by products produced by neighboring bacteria. The environment of the intestine can be altered by the compostion of the diet of the bird or by disease (e.g. coccidiosis, viral enteritis). As an example of the effect of diet on gut microflora, researchers have demonstrated that the colonization of some pathogens can be inhibited by feeding the bird complex sugars, like mannose or lactose.
The Nurmi concept. In 1973, Nurmi and Rantala demonstrated that treatment of newly hatched chickens with intestinal contents (feces) of adult chickens conferred resistance to infection by Salmonella infantis. Many scientists have since contributed to this area of research. To highlight some of the major findings:
A similar protective effect has been demonstrated in controlled studies against Escherichia coli, Campylobacter jejuni, Clostridium botulinum and Clostridium perfringens.
Mechanisms of protection. The exact mechanism by which CE products infer resistance to pathogens is still under investigation. Three mechanisms have been proposed to explain how CE products work:
1. Physical obstruction of attachment sites for salmonella by the native flora lining the intestine,
2. Competition for essential nutrients by the native flora limits the ability of salmonellae to grow,
3. Protective flora may produce volatile fatty acids (especially in the ceca) that limit the growth of salmonellae.
Defining and reproducing protective microflora in the laboratory. The first CE products were simply fecal contents from healthy adult chickens suspended in an aqueous solution and placed in the crop of the newly hatched chicks by gavage. Later, undefined mixtures of intestinal bacteria were serially cultured under anaerobic conditions. These preparations were shown to be highly effective. A concern about undefined cultures arises from their undefined nature. Serial subculture has been used for the dilution to extinction of harmful parasites or viruses that may be present in the original cultures. The known pathogens of poultry that are shed in the feces are not capable of withstanding the culture techniques for CE products. Screening tests for known pathogens are conducted but doubt has been raised that all pathogens can be identified by current screening methods.
Some research groups have developed defined mixtures of bacteria for use as CE products. The number of bacterial strains and species is critical to the effectiveness of the product. In general, products that contained a single or only a few bacterial strains have not been protective. There appears to be difficulty in maintaining a stable culture of numerous strains of bacteria over long periods of time. Some research groups have addressed this issue by applying continuous culture techniques in the production of CE products. However, if the culture technique limits the number of bacterial strains that can be maintained and grown in the culture, then the efficacy of the resulting product will be reduced.
The methods used to culture the component bacteria also affect the protective qualities of the product. And, the composition of the intestinal microflora that will serve as the origin of a cultured product, varies from bird to bird. Intestinal flora from healthy commercially reared chickens has proved superior to that from Specific Pathogen Free chickens. Additionally, there may be batch to batch variation in CE products depending on length of time the bacteria have been grown in culture. Clearly, quality control measures are extremely important for any products being offered on a commercial basis.
In a 1993 review article, Stavric and D'Aoust compared undefined and defined CE products for prevention of salmonella in poultry. They concluded that the efficacy of either type of product was much more variable in field than in laboratory tests and overall, undefined CE products were more efficacious than defined culture products. Products that showed efficacy against salmonellae were not protective against campylobacter infection.
Administration of CE products. In laboratory studies, the protective microflora is usually applied directly into the crop of the chick by gavage. For commercial application this technique is not feasible, therefore, CE products have been produced in liquid and lyophilized (dried) forms for practical use. In field studies, CE products have been administered in the drinking water, by spraying hatching eggs or chicks in the hatching trays or shipping boxes, within feed slurries, or sprayed on agar plates for the chicks to eat. All methods have had some success but no method has been 100% effective.
Use of CE products in commerical poultry. The use of CE products to protect newly hatched, highly susceptible chicks or poults being placed into commercial production systems could be of great benefit in reducing colonization and disease caused by paratyphoid salmonellae. If this protection translated into a reduced prevalence of food borne pathogens at harvest, this could also be of great value in reducing carcass contamination.
The use of CE products to restore a protective microflora following disruption of the intestinal bacteria by a disease, such as viral enteritis or coccidiosis may also prove to be a helpful husbandry practice. Alterations of intestinal flora due to stress in poultry flocks from transport, handling, vaccination, molting, chilling or heat stress may also be treated by CE products.
Effect of feed or water additives. The effect of feed additives such as antibiotics and coccidiostats regularly fed in commercial poultry diets and the effect of antibiotics used for disease treatment on the protection inferred by CE products must also be considered because antibiotics can alter intestinal flora. The presence of high levels of chlorine or other disinfectants in water available to poultry flocks may also warrant investigation. Stavric and D'Aoust reported that medicated feed containing about 200 ppm of bacitracin, furazolidone, gallimycin, penicillin/ streptomycin, chlortetracycline and tylosin, or 10 ppm of nitrivin did not adversely affect the efficacy of CE treatment. Common antibiotic feed additives used as growth promotants (5-50 ppm) had mixed effects on CE treatment. For example, bacitracin or virginiamycin improved the performance of CE cultures, flavomycin had no effect and avoparcin reduced the level of protection.
Conclusions. The positive benefits from commercial preparations of CE cultures are well accepted in Europe after more than 10 years of commercial use. CE products have been efficacious against colonization by numerous salmonellae serovars, including Salmonella enteritidis PT4, but not against campylobacter.
For U. S. poultry producers, competitive exclusion provides an opportunity for protecting poultry against pathogenic bacterial colonization, particularly salmonellae. The microflora of the intestine are in a dynamic state, undergoing continuous change, and subject to alteration by numerous forces. Therefore, the use of CE products is not a panacea against salmonellae infection throughout the life of the bird, however, in conjunction with good husbandry, CE products can make a valuable contribution to flock health and the safety of poultry products as food. Continued research in this area to identify the specific mechanisms by which CE products infer protection and to improve methods of delivering the product in commercial situations should contribute to the successful use of these products.