Feed Additives

Feed Additives

Modern intensive poultry production has achieved phenomenal gains in the efficient and economical production of high quality and safe chicken meat, eggs and poultry bioproducts. 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.

Feed enzymes

Enzymes are proteins that facilitate specific chemical reactions. After completion of the reaction, the enzyme disassociates and becomes available to assist in further 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 feedstuffs or to reduce anti-nutritional factors in feed that limit digestion.

Some cereal grains (rye, barley, wheat, sorghum) have soluble long chains of sugar units (referred to as soluble non-starch polysaccharides – NSP) that can entrap large amounts of water during digestion and form very viscous (thick gel-like) gut contents. Enzymes that are harvested from microbial fermentation and added to feeds can break these bonds between sugar units of NSP 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; and 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).

Commercial enzymes are also produced that significantly reduce the negative effects of phytates. Phytates are plant storage sources of phosphorus that also bind other minerals, amino acids (proteins) and energy and reduce their availability to the bird. Ongoing research will develop enzymes that are more effective in maintaining function under a wider range of processing and digestive conditions. New enzymes may include those capable of reducing toxins produced during feed spoilage (mould growth in grains) and facilitating digestion of carbohydrates currently not available to simple-stomached animals (poultry, pigs, humans) such as cellulose, lignin and chitin. New feed additives are rapidly adopted by the poultry industry and have facilitated the development of significant new technology to advance the use and availability of in-feed enzymes.

Antioxidants

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 defined as 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 microbiota. 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 the host animal. When entering the gut, prebiotics serve as a substrate for the endogenous beneficial bacteria thus can promote competitive exclusion of pathogenic microbes and selective colonization by beneficial microbes. 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 and 3) producing a systemic effect on stimulation of immune responses.