There is a global movement in the poultry industry away from prophylactic/Antibiotic Growth Promoters (AGP) due to concerns over antimicrobial resistance and posing a potential threat to human health. The use of antibiotics in feed for growth promotion has long been restricted in the European Union (EU). Policy around raising chickens without antibiotics varies among countries. For instance, in many countries such as Canada and the USA, there are niche markets and premium incentives for antibiotic-free production. Exporting countries such as Brazil and Thailand need to match the legislative requirements of importing countries, such as EU countries, regarding antibiotic usage in animal products. In developing countries, although consumers’ demand for antibiotic-free products might be less than in other areas, global chain restaurants might demand antibiotic-free products based on their policies.
Regardless of the motivation for moving away from antibiotics, the objective is to maintain animal health, production efficiency, profitability, and food safety. Removing AGP from poultry diets can provide an opportunity for a wide range of potential pathogens to survive and grow. There has been a lot of research looking at possible alternative compounds such as organic acids, probiotics, prebiotics, synbiotics, enzymes, phytogenics, antimicrobial peptides, hyperimmune egg antibodies, bacteriophages, clay, metals, and essential oils to maintain or improve poultry health and performance.
A practical AGP alternative should be economically feasible, simple to apply consistently under field conditions, be accepted by consumers, and have a positive effect on growth and feed efficiency by modulating the microbiome and immune responses in the host without promoting microbial resistance. The first step to optimizing the use of AGP alternatives is to understand the mechanism of action of AGP which will help find appropriate AGP alternatives. Table 1 summarizes some bullet points about the mechanism of action and explains AGP and some AGP alternatives in poultry nutrition.
Table 1. Explanation and mode of action of Antibiotic Growth Promoters (AGP) and some AGP alternatives
| Additive | Explanation | Mode of action |
| AGP | Antibiotic Growth Promoters have been widely used in animal production for decades for two main reasons: 1. therapeutically to improve the health and well-being of animals 2. prophylactic purposes and to improve growth rate and feed conversion efficiency | 1. Shifts in microbiota composition (structure and diversity) in the gut 2. Inhibit growth of organisms that produce excess amounts of ammonia and other toxic nitrogenous compounds in the intestine 3.Increase availability or absorption of specific nutrients 4. Favor the growth of nutrient-synthesizing microbes or suppress nutrient-destroying microbes 5. Anti-inflammatory role of AGP reduces maintenance cost associated with turnover of the intestinal epithelium (lining) and directs it toward production |
| Probiotics | “Mono or mixed cultures of live organisms which when administered in adequate amounts confer a health benefit to the host” (FAO/WHO, 2001). Administration methods: Feed Water Spraying on chicks, Embryonated eggs Some research showed that probiotics application via water was more efficacious than through feed. However, if any additive is going to be administered through water, proper water treatment protocols should be followed. We discussed some water cleaning protocols regarding biofilm cleaning and water treatment in our previous issues. | 1. Balancing the gut microflora through competitive exclusion (reduces the colonization of harmful bacteria by introducing beneficial microbes) 2. Regulation of immune responses 3. Reducing toxic amine production and ammonia levels in the gut 4. Help with development of intestinal function and increase in intestinal villus height and crypt depth 5. Help in digestion and nutrient retention by increasing digestive enzyme activity and improving the breakdown of indigestible nutrients |
| Prebiotics | ‘Non-viable feed components that confer a health benefit on the host associated with modulation of the microbiota.’ Prebiotics are either derived from plants or synthesized by microorganisms. The most important characteristic of an ideal prebiotic is the ability to selectively enrich beneficial microorganisms associated with health and well-being. | 1. Prevent colonization of harmful microbes by a. binding directly to pathogens and excluding them from the gut b. competitive exclusion i. promoting the growth of beneficial microbes i.i. stimulating the beneficial bacteria to produce bacteriocins and lactic acid. 2. The fermentation of prebiotics by microflora leads to the production of Short Chain Fatty Acids (SCFA) that act as energy sources for intestinal epithelial cells and thus maintain the integrity of the gut lining. 3. Modulate luminal or systemic aspects of the host immune system |
| Synbiotics | Additives that combine the use of probiotics and prebiotics such that they act synergistically | Modulate the intestinal microbiota composition and increase villi height and crypt depth in the intestinal mucosa |
| Organic acids | Administration through the feed or drinking water. Can be used either individually as organic acids or their salts (sodium, potassium, or calcium) or as blends of multiple acids or their salts. Using a blend of organic acids has shown better results than using them individually. Sometimes results of using organic acids are not consistent, which can be due to various factors such as inclusion rates, the source of the organic acids, and the buffering capacity of other dietary ingredients. If you are adding organic acids to water, make sure to follow a proper water treatment program and flush the drinker lines frequently. Overusing acids in water can create mold problem in water lines in the barn | 1. Reduce the pH level of the upper gastrointestinal tract (crop, proventriculus, gizzard). 2. Alter the gut microflora by a. directly killing through cell-wall penetration b. indirectly modifying pH and reducing the numbers of harmful bacteria c. increasing acid tolerant beneficial species such as Lactobacilllus spp. d. reducing competition for nutrients by the altered microbes. 3. Increase nutrient digestibility by a. elevating protein and dry matter retention b. improving mineral absorption and phosphorus utilization 4. Improve gut health through providing energy (e.g. SCFA) for intestinal lining cells |
| Enzymes | Biologically active proteins. When including enzymes in a diet, the diet should be carefully formulated considering the enzyme matrix value. To get more information about how to use enzymes matrix value in diet formulation, follow the instructions on our previous article. Variable results have been reported with the use of enzymes that can be attributed to the differences in the enzyme type, source, amount of enzyme used, presence of enzyme side effects, diet composition, and genetic variations among animals. | 1. Increase in the digestibility of nutrients that are not digestible by host enzymes (e.g. phytic acid). 2. Elimination of the nutrient-encapsulating effect of cell-wall polysaccharides and an increase in the availability of starches, amino acids, and minerals. 3. Inactivation of anti-nutritional factors such as phytic acid and soluble Non-Starch Polysaccharides (NSP) and reduced intestinal viscosity. 4. Increase in the solubility of non-soluble NSP and promotion of cecal fermentation. 5. Indirect effect on the composition of the gut microbiota |
| Phytogenics (Phytobiotics or Botanicals) | Natural bioactive compounds that are derived from plants. Incorporated into animal feed to enhance productivity. Depending on the process used to derive the active ingredients, phytogenics can also be classified as essential oils (volatile lipophilic substances obtained by cold extraction or by steam or alcohol distillation) and oleoresins (extracts derived by non-aqueous solvents). To increase the body weight gain and improve the feed efficiency, a mixture of various herbs might be necessary | 1. Antimicrobial and antioxidant properties. 2. Increase intestinal and pancreatic enzyme production and activity and increase bile flow. 3. Increase intestinal villi height and expand absorptive surface of the intestine, maintaining the intestinal barrier function |
| Hyperimmune egg yolk antibodies (IgY) | Produced by repeated immunization of hens with specific antigens and collection of antibodies thereafter from their egg yolks. Have been used in the prevention and treatment of various enteric diseases in humans and animals. Has some beneficial intergenerational effects in broiler breeders that increased body weight in their progeny. In a research, breeder hens were injected with jack bean urease. The results showed that the urease antibodies maternally transferred to the progeny decreased ammonia production in the intestinal tract by inhibiting bacterial urease enzyme and improving growth. | 1. Anti-inflammatory role 2. Immune-modulation effects |
| Bacteriophages | Highly species-specific viruses that kill harmful bacteria. Exhibit no harmful activity against animal and plant cells (safe antibiotic alternatives)have been used to prevent and treat various bacterial diseases in humans and animals | Kill bacteria through the production of endolysins and the subsequent lysis of the bacterial cells |
| Clay | Clay minerals (phyllosilicates) are formed by a net of layers containing molecules of silicon, aluminum, and oxygen, and interconnected by hydrogen bonds or a group of cations. Some natural extracted clays are bentonite, zeolite, and kaolin. Has the ability to decrease the litter moisture. | Bind and remove toxins (e.g. aflatoxins), anti-nutritional components, heavy metals, and pathogenic organisms. Improve nutrient digestibility by reducing digest transit time. |
Despite the well-demonstrated beneficial effects of many antibiotic alternatives in poultry health and performance, results vary significantly from farm to farm. Maximizing the value of feeding AGP alternatives starts with sound management practices including vaccinations, robust chick quality and best management practices. Work with your nutritionist to tailor an AGP alternative strategy for your farm.
References
- FAO/WHO. 2001. Probiotics in Food, Health and nutritional properties and guidelines for evaluation. link
- G. Huyghebaert, R. Ducatelle, and F. Van Immerseel. 2011. An update on alternatives to antimicrobial growth promoters for broilers. The Veterinary Journal. 187: 182–188 link
- J. J. Dibner and J. D. Richards. 2005. Antibiotic Growth Promoters in Agriculture: History and Mode of Action. Poultry Science 84:634–643. link
- U. Gadde, W. H. Kim, S. T. Oh, and Hyun S. Lillehoj. 2017. Alternatives to antibiotics for maximizing growth performance and feed efficiency in poultry: a review. Animal Health Research Reviews 18(1): 26–45 link
