A better understanding of the bacterial populations in the lower gastrointestinal tract can help develop poultry feeding programs to reduce production losses

Dr. Curtis Novak


Antibiotics can and are frequently used therapeutically and prophylactically for the treatment of disease in poultry.

It was back in the early 1900’s when the antibiotic pioneers first discovered the chemical substance (Salvarson) that cured human disease while prontosil rubrum was discovered to protect mice and rabbits from infection by streptococci and staphylococci.

It wasn’t until 1946 when the first recorded research indicated the positive effects of antibiotics on chicken growth which was originally believed to be related to the discovery of vitamin B12 . However, increasing pressure to reduce or eliminate the use of antibiotics in feed is occurring due to the negative human health issue of antibiotic resistance. In 1994, it was first shown that vancomycin resistance enterococci (GRE) could be isolated to farm animals in Great Britain and was suggested that farm animals could be a reservoir for the GRE infection. In the study, 62 isolates of GRE were isolated from non-human sources of which 22 were from farm animals and 5 from uncooked chicken. Roy and coworkers (2002) also isolated Salmonella from poultry products, poultry, and poultry environment and found that 91 of the 92 samples tested were resistant to erythromycin, lincomycin, and penicillin.

A number of strategies to reduce the use of antibiotics in feed have been explored, including improved biosecurity, vaccination, genetic selection, competitive exclusion (CE), enzymes, organic acids and phytogentics. Vaccination can be effective, but the avian immune system may be compromised when vaccinating to reduce S. enteritidis at day 1, and it was subsequently determined that the optimum vaccination time was at day 28. Chicks are immunologically naive and prone to rapid and persistent colonization by beneficial and pathogenic bacteria in the first 3 to 4 weeks of life indicating that CE may be a beneficial approach. One CE approach utilizes a complex mixture of bacteria derived from the gut of healthy birds subsequentially orally administered to day old birds to establish a beneficial microflora. This microflora in turn prevents the colonization of pathogenic microorganisms such as Salmonella and E. coli. Probiotics are defined as “live microbial feed supplements which beneficially affect the host animal by improving its intestinal microbial balance” (Fuller, 1989).

A number of researchers have reported that the addition of probiotics to the diet of broilers and layers leads to improved performance.

Another CE product (Prebiotics) uses the characteristic of mannose-specific binding with fimbriae of pathogenic gram-negative bacteria such as E. coli and Salmonella. These bacteria grow to express the type 1 fimbria and adhere efficiently to the crop epithelium, lamina propria, and apical surfaces of intestinal villi. The adhesion was inhibited by α- methyl-D-mannoside. Mannan oligosaccharides (MOS), derived from mannans on yeast cell wall, are non-digestible for monogastric animals and can be utilized by lactic acid bacteria. MOS also bind the fimbriae of pathogenic bacteria to prevent them from attaching and colonizing on small intestine mucosa. Adhered bacteria are subsequentially washed out of the small intestine with the flow of intestinal contents. Diets supplemented with MOS significantly impact the chicken’s intestinal microflora and reduce susceptibility of S. Enteritidis colonization.

Enzymes are widely used today in feeding programs to increase the availability of a number of nutrients such as phosphorus, protein, amino acids and energy. Enzymes can be an effective tool in maintaining a healthy gut. The beneficial effects of enzymes are likely the result of an increase in digestive efficacy resulting in a change in quality and quantity of substrates for the host and micro flora. Short change fatty acids produced by the digestion of fiber can be a food source for certain beneficial bacteria. This in turn can increase the competitive nature of those bacteria to foster a positive environment in the gut. Unpublished research by Novak and Sun utilizing a commercially available feed grade enzyme revealed an increase in the relative amounts of bifidobacteria (beneficial) while reducing clostridia perfringens in the gastro intestinal tract of broilers.

Organic acids (individual and blends – OA) have been evaluated and are reported to have an affect on microbial populations in the gastro intestinal tract and may be an option when feeding animals without AGPs. Dibner and Buttin, 2002 reviewed the use of OA in poultry feeds and reported OA can reduce acid-intolerant bacterial species such as E. Coli, Salmonella and Campylobacter, but the variability associated with detecting a positive affect of their use is much larger compared to antibiotics and needs further evaluation.

Phytogenic feed additives are plant-derived products used in animal feeds to improve or maintain performance of livestock animals. To further classify these plant-derived products, they can be described with respect to their origin and processing. Such as: herbs (flowering, nonwoody, and nonpersistent plants), spices (herbs with an intensive smell or taste commonly added to human food), essential oils (volatile lipophilic compounds derived by cold expression or by steam or alcohol distillation), or oleoresins (extracts derived by nonaqueous solvents). As noted by the increase in scientific publications since 2000, this group of feed additives has gained increasing interest for use in swine and poultry feeds. This increase in interest is probably due to the ban of AGP in Europe in 1999. Mechanisms of improved performance determined thus far, is through amelioration of feed properties, promotion of the animals’ production performance, and improving the quality of food derived from those animals.

There are a number of things to evaluate when developing a non AGP program. In the poultry and swine industry, we need to move toward a better understanding of the bacterial populations in the lower gastrointestinal tract to further develop feeding programs to reduce the loss in production without the use of an AGP. We need to learn how to feed the bacteria to work for the animal, not against it. Lastly, a combination of aforementioned products and improvements in management, vaccination programs and or genetics will be most effective in maintain the growth and efficacy of poultry in the future.

(From Proceedings of the “Midwest Poultry Federation Convention”, St. Paul, Minnesota, U.S.A.).