Alternatives to Antibiotic Growth Promoters

Antibiotics as growth promoters played a crucial role in the growth of the poultry industry over the last few decades by maintaining gut health which increased feed efficiency and egg production.
However, the use of antibiotics as growth promoters is now causing concern due to the presence of antibiotic residues in livestock products and the emergence of superbugs – bacteria that are resistant to multiple antibiotics. A report on surveillance of antimicrobial resistance by WHO cautions about the growing threat of antimicrobial resistance and antibiotic treatment is at risk if remedial measures are not taken immediately. It called for the reduction of antibiotic usage in both Humans and livestock. In addition, there is a growing demand from consumers for Antibiotic-free chicken and eggs. With the ever-increasing genetic potential and advancements in nutrition with tremendous growth in poultry production, the biggest challenge for the industry is to produce Antibiotic residue-free Chicken in general or Antibiotic-free Chicken in specific.

Many alternatives for AGPs have been explored for over a decade. The term “Eubiosis” is gaining significance referring to the optimal balance of microflora in the gastrointestinal tract and the supplements which help in attaining Eubiosis is termed “Eubiotic Feed Supplements” such as Organic acids, Probiotics, Prebiotics, Essential Oils, Phytobiotics, Medium Chain Fatty Acids, Trace Minerals, and Vitamins.

Organic Acids
The addition of free organic acids and their salts in feed reduces the contamination and recontamination of feed and feed ingredients and enhances the secretion of digestive enzymes which improves the digestibility. These acids exert antimicrobial activity at the intestinal level maintaining an optimal balance of microflora. The usage of Butyric acid salt in its protected triglyceride-coated form has increased significantly due to its Target Release Action and for being a source of energy for enterocytes assisting in maintaining the health of gut epithelium which improves absorption. The usage of diformate salts as a feed additive is approved and its usage is increasing due to its effective antimicrobial effect and sustained release action.

Probiotics are defined as animal feed supplements containing live microorganisms which have a beneficial effect on the host by affecting gut microflora. The mode of action of probiotics is by competitive exclusion and antagonism. Upon consumption, probiotics reach the gut effectively blocking the intestinal receptors, and competitively exclude the pathogenic bacteria from the gut. Further, they prevent the attachment and proliferation of pathogenic bacteria by forming an aggregation. Once aggregated, they create microecology in the gut that is hostile to pathogenic microbes. Probiotics also produce and secrete antimicrobial metabolites (Bacteriocins) and prevent enterotoxin absorption. Probiotics can produce Vitamins B complex and K and have a role in stimulating an immune response. Probiotics decrease the urease enzyme activity inside the gut and reduce the production of toxic amines and ammonia. The efficiency of probiotics depends on the selected microbes, their concentration, and their stability.

Prebiotics are non-digestible feed ingredients that benefit the host by supplying nutrients to the beneficial microbes and competitively excluding the pathogenic bacteria by adhering to intestinal receptors. It also exerts its antimicrobial effect by tricking the pathogenic bacteria into attaching to the prebiotics rather than intestinal mucosa and prevents pathogenic bacterial colonization inside the gut. It has an immunomodulatory effect by direct action on macrophages and facilitates T-cell proliferation. The predominantly used prebiotics are Mannon oligosaccharides(MOS) and β-glucans.

Essential oils
Essential oils are recognized as a potential replacement for AGPs. These are the active ingredients present in various plant species, like Eugenol, Thymol, Piperine, Cinnamaldehyde.

The antibacterial activity of essential oils is not the result of one specific mode of action, but a cumulative effect on many different targets in various parts of the cell. It disintegrates the membrane of bacteria leading to the release of membrane-associated materials from the cells to the external medium, impairs the bacterial enzyme systems, and exerts its effects on the bacterial genetic material too. It also inhibits cell wall division and interferes with metabolism. Further, essential oils stimulate the growth of beneficial microbes and limit the number of pathogenic bacteria in the gut of poultry. Essential oils increase digestive enzyme secretions and have antioxidant and Immunomodulatory action.
Phytobiotics like turmeric and garlic are gaining importance among poultry producers due to their antimicrobial, and immunomodulatory effect along with improved digestive enzyme secretions.

Medium Chain Fatty acids
The usage of medium-chain fatty acids as an Eubiotic feed supplement has already gained significance in the EU due to its bactericidal properties and as an energy source for enterocytes. MCFA causes bacterial cell lysis through the invasion of the bacterial cell membrane and subsequent pH drop. It inhibits the production of lipases by the bacterium and prevents its colonization in the gut as lipases are needed for bacteria to attach to the intestinal mucosa.

Trace Minerals and Vitamins
Increased dosage of Trace Minerals (Se, Zn & Cu) and Vitamins (E & A) in the feed is practiced in the present scenario due to their antioxidant and immune modulatory effect.

Considerable research is also being carried out on Lysozymes, Lactoferrins, and bacteriocins as an alternative to AGPs. Higher inclusion costs are affecting its usage along with practical implications as of now.
Any single Eubioitc feed supplement may not replace the effect of AGP, but the judicious combination of the above aforesaid Eubiotic feed supplements has tremendous potential to replace AGPs in years to follow. A lot of trials should be conducted further to arrive at a fruitful combination of eubiotic feed supplements that can effectively replace AGPs.

by Dr J Sujith Reddy, Neospark Drugs and Chemicals Private Limited