Introduction
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 maximize the health and well-being of the birds and minimize the impact of the industry on the environment. The use of feed additives has been an important part of achieving this success.
Defining feed additive
The diet of animals and humans contain a wide variety of additives. However, in poultry diets these additives are primarily included to improve the efficiency of the bird’s growth and/or laying capacity, prevent disease and improve feed utilization. Any additives used in feed must be approved for use and then used as directed with respect to inclusion levels and duration of feeding. They are also specific for the type and age of bird being fed.
Common feed additives used in poultry diets include antimicrobials, antioxidants, emulsifiers, binders, pH control agents and enzymes. Sometimes diets will also contain other additives used in diets for humans and pets such as flavour enhancers, artificial and nutritive sweeteners, colours, lubricants, etc. Within each one of these classes of additives there can be dozens of specific additives manufactured and distributed by a wide variety of companies. Again, all ingredients and additives must be noted on the label and their use and inclusion levels meet the standards as defined by law. 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 article will highlight a few important feed additives and their use in the poultry industry.
Type of feed additives
- Sensory additive is an additive that stimulates the appetite, improving the voluntary intake of a diet. Eg. Feed flavors or sweeteners.
- Nutritional additive provides specific nutrients for an animal for optimal growth. Eg. Vitamins and aminoacids.
- Zootechnical additive improves the nutritional value of a diet. It doesn't give nutrients directly to the animal, but through its diet. This category includes, among others, enzymes and certain phytogenics.
- Coccidiostats and histomonostats control the health of poultry through direct effects.
Antimicobials
Growth promoting hormones are not used in the poultry industry. The efficient growth and egg productivity of commercial poultry has been achieved over the last 50 years through traditional animal breeding techniques (genetic selection – not genetic engineering) and improved nutrition and management (including health and housing) practices.
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 (should a need for antimicrobials arise all eggs laid during the treatment and withdrawal period cannot be sold) 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 bioproducts as well as the negative impacts associated with their excretion into the environment. The European Union has moved towards a complete ban of in-feed antimicrobials for these reasons. Development of alternatives to the present in-feed antimicrobials is an exciting area of current research world-wide. In all cases, it will be necessary to minimize disease challenges, strengthen the bird’s natural defenses and optimize the diet to provide a balance of required nutrients for the bird’s changing needs. All of these may be influenced by using feed additives.
Feed enzymes
Enzymes are proteins that facilitate specific chemical reactions; following this the enzyme will disassociate and be 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 feed stuffs 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 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 (more interaction of digestive enzymes with feeds and more complete digestion), absorption (better contact between digested feed nutrients and the absorptive surface of the gut) and health (reducing moisture in manure and 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. The antioxidative status of an animal depends on many different factors. The animal itself represents a homeostatic system with the available enzymes. With the feed it ingests nutrients with a variable potential for oxidation, the polyunsaturated fatty acids (PUFA) representing the highest risk. With the feed it also ingests substances like iron, copper or phytase that can catalyze the nutrient oxidation.
Finally antioxidants like tocopherols, carothenes, flavonoids etc. protect the sensible substances (Fig. 2). The different antioxidants can have a variable activity. This depends on the polarity and solubility, but also the place of activity. Some antioxidants are used to protect the nutrients in the feed during storage. Others have their main activity in the digestive tract where they may also help that the substances sensible for oxidation can be absorbed. In the intermediate metabolism antioxidants are responsible for many functions like reduced aging or the protection of intact membranes. In farm animals antioxidants can have a direct influence on the product quality.
Fig. 2 Activity of antioxidants in monogastric animals (Casper Wenk, 2002)
Future perspectives
Many additives have been a normal part of diets for animals and humans. It is only recently that we have come to recognize and understand their importance in achieving high production and efficiency, maintaining health and wellbeing, improving product quality and safety and reducing the industry’s impact on the environment. More work is required to further identify the positive effects of additives and minimize the negative effects they may have if not used correctly or if they interact with other additives or feed ingredients. In particular, additives will play an essential role in maintaining the health of poultry in an era of no pharmaceuticals.
