Modern intensive poultry production has achieved phenomenal gains in the efficient and economical production of high quality and safe chicken meat, eggs and poultry byproducts. At the same time as making gains in production and efficiency, the industry has had to maximise the health and well-being of the birds and minimise the impact of the industry on the environment. The use of feed additives has been an important part of achieving this success.
common feed additives used in poultry diets include antimicrobials, antioxidants, emulsifiers, binders, pH control agents and enzymes. In some instances additives are added to the animal’s diet in order to enhance their value for human consumption, but mostly this is accomplished by use of natural ingredients containing significantly higher levels of these nutrients that can be deposited directly into meat and eggs. This fact sheet will highlight a few important feed additives and their use in the poultry industry.
Antimicrobials
Antimicrobials have been used extensively in intensive poultry operations to minimize disease and improve growth and feed utilization. However, the industry is currently evaluating alternatives to chemical therapeutics. It should be pointed out that antimicrobial practices do not extend to production of commercial eggs and the meat industry must adhere to stringent guidelines with regard to drug withdrawal periods before marketing.
There is much controversy in regard to the impact of antimicrobials in animal diets on the development of resistant strains of microbes that could directly impact human health and carry over into meat and byproducts. Alternatives to in-feed antibiotics mainly include acidifier, probiotics, prebiotics, herbal products, immune-modulators and also feed enzymes.
Feed enzymes
Enzymes are proteins that facilitate specific chemical reactions.Although animals and their associated gut microflora produce numerous enzymes, they are not necessarily able to produce sufficient quantities of specific enzymes or produce them at the right locations to facilitate absorption of all components in normal feed stuffs or to reduce anti-nutritional factors in feed that limit digestion.
Enzymes that are harvested from microbial fermentation and added to feeds can break bonds between sugar units and significantly reduce the gut content viscosity. Lower viscosity results in improved digestion as there is more interaction of the digestive enzymes with feeds and therefore more complete digestion; improved absorption as there is better contact between the digested feed nutrients and the absorptive surface of the gut.
improved health as the moisture and nutrient levels in the manure are reduced which reduces the nutrients available for harmful gut microflora to proliferate and challenge the birds (e.g. necrotic enteritis, a chronic intestinal disease caused by Clostridium perfringens, resulting in reduced performance, mortality and the main reason we currently use in-feed antimicrobials).
Anti-oxidants
There are a variety of sources of reactive oxygen species (free radicals) in normal metabolism as well as those coming directly from feed ingredients. Oxidative stress can disrupt normal cellular function, damage tissues (also associated with the development of cancers) and reduce health status. Antioxidants bind these molecules and reduce their potential damage.
Acidifiers
Feed acidifiers are added to the feed to lower the pH of the feed and consequently the gut environment. A lower pH has the potential to inhibit or partly restrict the growth of pathogenic intestinal microbes. Acidifiers exist both as organic or inorganic acids or associated salts. They can exert their antimicrobial action both in the feed and throughout the gut.
Health and performance promoting effects have been shown for a number of organic acids such as formic, fumaric, citric, propionic and lactic acids.However, the overall benefits of organic acids greatly depend upon the form of administered organic acid (protected or unprotected), uncontrolled variables such as buffering capacity of ingredients, presence of any other microbial agent, cleanliness of production environment, and heterogeneity of microbes.
Probiotics
Probiotics are live mono or mixed culture of microorganisms which are non-pathogenic, resistant to gastric and bile acids, and when ingested can beneficially affect the host animal by improving the characteristics of intestinal microbe. The main proposed modes of action of probiotics include:
1) antagonistic action towards pathogenic bacteria by secretion of products which inhibit their development, such as bacteriocins, organic acids and hydrogen peroxide.
2) competitive exclusion which represents competition for locations to adhere to the intestinal mucous membranes and in this way pathogenic micro-organisms are prevented from inhabiting the digestive tract.
3) competition for nutritious substances. Probiotics have also been reported to exhibit immunomodulatory properties mostly through manipulation of gut microbiota composition and consequently affecting both innate and adaptive immunity. In this way, they create conditions in the intestine which favour useful bacteria and inhibit the development of pathogenic bacteria.
Prebiotics
Prebiotics are defined as indigestible food ingredients which stimulate the growth or activity of a selected number of bacteria in the gastrointestinal tract of host animal. Among the known prebiotics, mannan-oligosaccharide (MOS) fructo-oligosaccharide (FOS) and galacto-oligosaccharide (GOS) have extensively been tested in poultry. Prebiotics proposed mechanism of actions include:
1) lowering gastrointestinal tract pH through lactic acid production.
2) Inhibiting the colonization of pathogens.
3) Producing systemic effect on stimulation of immune responses.
