Feed additives 
with a track record

In the making of compound feed, many ingredients and especially micro-ingredients are used. This is based on costs and presumed effectiveness. [Photos: Henk Riswick]
In the making of compound feed, many ingredients and especially micro-ingredients are used. This is based on costs and presumed effectiveness. [Photos: Henk Riswick]

There are plenty of feed additives on the market. Some have an impact, some less of one. The nutritionists at Aviagen describe the performance of key additives that have been tested in trials, the results of which have been published in peer reviewed journals.

The beneficial effects of commercially available poultry feed additives have been extensively promoted, but deciding which, if any, may be of economic benefit to an individual operation can be challenging. Innovative products that might result in better performance under one specific set of conditions may not yield the same results under a different set of conditions. Sufficient repetition of experimental studies in different labs and proven efficacy in commercial trials are the best way of establishing which feed additive may be useful in a given operation.

Prebiotics and probiotics

Prebiotics are non-digestible feed ingredients, such as oligosaccharides, that positively affect the activity and growth of beneficial microflora in the gastrointestinal tract. Capable of surviving under a wide range of environmental conditions, the 
bio-efficacy of prebiotics tends to be less variable than that of probiotics, which are fed as a culture of live micro-organisms.

The mode of action of these two products is similar in that they both work by increasing the amount of beneficial (‘good’) microflora in the gut. For example, an increased number of lactic-acid-producing bacteria results in a higher production of short-chain fatty acids and this reduces the pH in the intestine, improving the absorption of certain nutrients such as protein, calcium and phosphorous.

In broiler chickens, the beneficial effects of prebiotics will depend on the level of inclusion, the type of oligosaccharide, and the composition of the basal diets. In broilers, fructo-oligosaccharides tend to have greater impact, as do mannano-oligosaccharides and inulin to a lesser degree. The addition of inulin and oligofructuose to the diets of broiler breeders has resulted in improved egg production and shell quality.

The addition of probiotics to the diets of both broilers and breeders is a viable strategy with generally positive results during periods of challenge. However, probiotics tend to give a less predictable effect than prebiotics because their efficacy is determined by the bird’s physiological state and product quality, which is sensitive to the environment. In addition, the presence of antibiotics or anticoccidials may affect probiotic activity.


The beneficial effects of commercially available poultry feed additives have been extensively promoted, but deciding which, if any, may be of economic benefit to an individual operation can be challenging.


Despite the fact the benefits of acidifiers (short-chain fatty acids) have been successfully tested across numerous research institutions, their inclusion in poultry diets has yielded mixed results. The method of administration (whether they are encapsulated or conjugated), inclusion level and environmental conditions influence the efficacy of these products.

Acidifiers reduce the pH of feed and the gastrointestinal tract, increase the absorption of calcium and protein, and inhibit the growth of pathogenic microbes in the gut. In broilers, fumaric, propionic, formic and butyric acid have been shown to improve FCR, although combinations of these seem to produce a more predictable result. In broiler breeders, the addition of acidifiers to the diet has consistently resulted in increased egg production and shell thickness in aged hens and during high environmental temperatures.


Effective biosurfactants, suspended in emulsions of water and oil, are useful for enhancing the digestibility of fatty acids and therefore, potentially, bird performance. Their effectiveness will depend on the type and levels of fats included in the basal feed, as well as the type of emulsion added.

Palm oil (80% of palmitic acid) at 3% inclusion with 0.03% of glyceryl polyethylene glycol ricinoleate has been shown to improve FCR and reduce the incidence of pasty vent in broilers; the likely mode of action was regulation of fatty acid production from the caeca (improved fatty acid digestion, reducing fat excretion). Similarly, high levels of palmitic acid (8%) or a mixture of palmitic acid (4%), oleic acid (4%) and cholic acid (0.2%) have been shown to increase dietary ME and improve FCR and body weight. The inclusion of the emulsifier lecithin at a level of 0.5% improved the performance of birds fed a diet with 1.5% soybean oil, yet increasing levels of lecithin (1-2%) did not improve the performance of birds fed 2-2.7% or 1-2% soybean oil. In laying hens, egg production and hatchability have been positively affected by the inclusion of 3% of lecithin due to better fat mobilisation from the liver to egg yolk.


The use of synthetic antioxidants to maintain feed quality has been tested extensively. For example, ethoxyquin has proven to reduce fat rancidity and feed deterioration and is most effective when feeds are stored for long periods of time or when levels of peroxide (toxic by-products of rancidity) are equal to or higher than 4 mEq/kg of feed.

Vitamins A, E and C have antioxidant properties. A recent study has shown that, in breeders, Vitamin A reduces lipid degradation (peroxidation) in the yolk, leading to improved hatchability and fertility, and reduced early and late embryo mortality. The reduction of lipid peroxidation in eggs from broiler breeders fed canthaxantin is more accentuated when the eggs are stored for a prolonged time.

Vitamin E protects the high concentrations of polyunsaturated fatty acids found in sperm, aiding fertility in males. Studies completed in broiler breeder females have shown that feeding them vitamin E results in better egg production and hatchability. Reduced egg lipid peroxidation will allow for improved lipid utilisation by the embryo and young chick, although supplementing vitamin E to broiler breeders has not shown to improve viability and performance in the progeny chicks. In broilers, the addition of extra vitamin E to the diet mildly decreased the number of damaged fibres in the pectoral 
muscle of young broilers.

Under conditions of high environmental temperatures, high doses of vitamins A and E in poultry have resulted in improved performance. Vitamin C is most useful when environmental diseases or nutritional challenges are present. Yet improvements in performance are inconsistent; this inconsistency in performance may be linked to the instability of vitamin C during storage. The use of coating substances can significantly improve the storage stability of vitamin C and the consistency of performance benefits.


A standard feed does not exist, batches are increasingly tailor-made.


Carnitine is involved in the transport of fatty acids during the breakdown of lipids (fats) for the generation of metabolic energy. The addition of carnitine to the diets of broiler chickens might result in reduced abdominal fat and improved breast and/or thigh yield. The addition of carnitine to breeder diets may improve sperm concentration in roosters, as well as fertility and hatchability in breeder hens. The progeny of hens fed carnitine or the addition of carnitine to the diet of the chicks resulted in better yolk sac absorption.


Creatine naturally occurs in vertebrates and helps to supply energy to all cells in the body, particularly muscle. The use of creatine as an additive to all vegetable protein poultry diets (which have no naturally occurring creatine present) has recently been investigated. A precursor of creatine, known as guanidinoacetic acid, has been added to diets as it is less expensive and more stable than creatine itself. The addition of this additive to all-plant protein-based diets has proved effective in improving energy utilisation and FCR in diets with adequate ME levels, although benefits in low ME diets seem to diminish. The feeding of creatine or one of its precursors may also be beneficial in diets low in arginine. Because the synthesis de-novo creatine utilises arginine, this additive might also promote growth due to the sparing effect of arginine.


While the use of nucleotides has been shown to positively improve the growth and immune response of piglets, in broiler chickens their benefits for performance are limited. Physiological differences during the de-novo synthesis of nu-cleotides in mammals and birds might explain this difference; the need in chickens for additional nucleotides may be smaller than that of piglets. Furthermore, variations between sources of nucleotides derived from yeast might also contribute to the lack of positive responses observed in chickens.


Over the last 25 years, countless studies have been conducted reporting the benefits of exogenous enzymes in poultry feeds. As a consequence, there are a large number of commercially available enzymes for inclusion in poultry feeds. While not all enzymes have been shown to work consistently, the number of commercially available enzymes is so large that their use in poultry feeds is common practice nowadays. There are three broad categories of enzymes used in poultry feeds; Carbo-hydrases, which improve the digestibility of carbohydrates; proteases, which improve the digestibility of proteins and phytases, which make plant-derived phosphorus more available.

The use of phytases, for example, is widely accepted, well-defined and the benefits have been proven. It is well-known, for example, that the efficacy of cell wall degrading enzymes largely depends on the cereal used in the diet. On the other hand, the uses of other enzymes, e.g. proteases, are still not well-defined. The addition of exogenous proteases often does not result in a discernable benefit in performance and this lack of correlation between the digestibility of protein and the performance might suggest an over-stimulation of endogenous enzymes when exogenous proteases are added.

But the inclusion of proteases in lower doses and in combination with other enzymes (e.g. phytase and xylanase, a type of carbohydrase) has resulted in better, more predictable 
performance, suggesting synergy in the mode of action between enzymes.

Vitamin D

Vitamin D plays a crucial role in calcium metabolism. The inclusion in birds of cholecalciferol (D3), calcidiol (25-OH-D3), or calcitriol (1.25-OH2-D3) results in a positive response on eggshell quality. The addition of products containing vitamin D is most relevant in older hens. Furthermore, the inclusion of these additives in the water instead of feed has sometimes resulted in better response to improve the eggshell quality.


Feed additives broadly fit into several different categories, each category with a slightly different mode of action. All purport to have beneficial effects on digestive function; improving the digestibility of nutrients, improving gut microbe balance, protecting dietary nutrients from degradation and so on. While the benefits of some are well-proven and consistent, the effects and efficacy of others are less proven. Nevertheless, during periods of challenge, whether it is environmental, nutritional or managerial, these feed additives may provide some benefit for performance in both broilers and breeders.