Natural growth promoters (NGPs) are

feed additives A feed additive is an additive of extra nutrient or drug for livestock. Such additives include vitamins, amino acids, fatty acids, minerals, pharmaceutical, fungal products and steroidal compounds. The additives might impact feed presentation, hy ...

for farm animals.

Definition

Different categories of feed additives for farm animals are referred to as natural growth promoters (NGPs) or non-

antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention of ...

growth promoters. They are commonly regarded as favorable alternatives to antibiotic growth promoters (AGPs) in livestock production.

General benefits

The main advantage of NGPs over AGPs is that they do usually not bear any risk regarding bacterial resistance or undesired residues in animal products such as meat, milk or eggs. Addition of NGPs to feeds of farm animals may have a number of beneficial effects, including:

Mode of action

Acidifiers

Acidifiers, such as organic acids or their salts, are used to prevent microbial degradation of raw materials or finished feeds, especially under poor storage conditions (e.g. high moisture content, high levels of contamination with molds). Moreover, acidifiers may improve growth performance through establishment of low gastrointestinal pH conditions which support endogenous digestive enzymes and reduce undesired gut

microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...

s. Many dietary acidifiers are based on propionic acid, formic acid, lactic acid and others, either as single components or in combination. Some acidifiers also contain inorganic acids (e.g. phosphoric acid).

Probiotics

Probiotics are live microorganisms or viable spores which support the development of a beneficial gut

microflora Microbiota are the range of microorganisms that may be commensal, symbiotic, or pathogenic found in and on all multicellular organisms, including plants. Microbiota include bacteria, archaea, protists, fungi, and viruses, and have been found to ...

. Probiotic bacteria (e.g. from the

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

''Lactobacillus'', ''Bifidobacterium'', ''Enterococcus'') counteract undesired microorganisms such as ''Salmonella'' or ''E. coli'' by blocking receptors on the gut wall, production of antimicrobial substances or activation of the immune system.

Prebiotics

Prebiotics are carbohydrates which are indigestible for the host animal. On the other hand, they are selectively fermented by beneficial gut bacteria and, therefore, support a healthy gut microflora. These include fructose oligosaccharides (FOS) including

inulin Inulins are a group of naturally occurring polysaccharides produced by many types of plants, industrially most often extracted from chicory. The inulins belong to a class of dietary fibers known as fructans. Inulin is used by some plants as a mea ...

, transgalactose oligosaccharides (GOS),

xylooligosaccharide Xylooligosaccharides (XOS) are polymers of the sugar xylose. They are produced from the xylan fraction in plant fiber. Their C5 (where C is a quantity of carbon atoms in each monomer) structure is fundamentally different from other prebiotics, whi ...

s (XOS) and soy oligosaccharides such as

stachyose Stachyose is a tetrasaccharide consisting of two α--galactose units, one α--glucose unit, and one β--fructose unit sequentially linked as gal(α1→6)gal(α1→6)glc(α1↔2β)fru. Together with related oligosaccharides such as raffinose, stach ...

verbose Verbosity or verboseness is speech or writing that uses more words than necessary. The opposite of verbosity is plain language. Some teachers, including the author of ''The Elements of Style'', warn against verbosity; similarly Mark Twain and E ...

and

raffinose Raffinose is a trisaccharide composed of galactose, glucose, and fructose. It can be found in beans, cabbage, brussels sprouts, broccoli, asparagus, other vegetables, and whole grains. Raffinose can be hydrolyzed to D-galactose and sucrose by ...

Mannan oligosaccharide Mannans are polymers containing the sugar mannose as a principal component. They are a type of polysaccharide comprise hemicellulose, a major source of biomass found in higher plants such as softwoods. These polymers also typically contain two o ...

s are sometimes included as prebiotics but are not fermentable. This was confirmed by Smiricky-Tjardes ''et al.'' at the University of Illinois and so might be more appropriately termed immunosaccharides since they act as decoys for pathogen attachment (''Salmonella'' and ''E. Coli'') and result in increased immunoglobulins (IgAs) at intestinal level.

Synbiotics

Combined administration of probiotics and prebiotics, referred to as synbiotics, is supposed to cause synergistic effects in terms of gut health and performance.

Phytogenics

Phytogenics are derived from herbs, spices or aromatic plants and have shown antimicrobial, antifungal, antiviral, antioxidant or sedative properties. They are known for their appetizing effects, since they increase the palatability of the feed and stimulate endogenous digestive enzymes. Moreover, phytogenics have a pronounced impact on the gut microflora.

Tannins

Tannins are polyphenolic compounds produced by plants, ranging in concentrations from <2% to more than 20% of dry weight and may protect plants from herbivore, increase resistance against pathogens, or protect tissues such as wood against decay. In-vitro and in-vivo results suggest that two of the most abundant and common source of tannins, chestnut (''Castanea sativa''; hydrolyzable tannins) and quebracho (''Schinopsis lorentzii'', condensed tannins) extracts, are effective to reduce and control infection. Moreover are considered a natural alternative to AGPs due to the difficulty of bacteria to develop resistance against the diverse range of molecules that contain these plant compounds.Redondo, L. M., et al. "Hydrolyzable and condensed tannins resistance in Clostridium perfringens." Anaerobe 34 (2015): 139-145.

Feed enzymes

Animal feeds contain varying levels of indigestible nutrients and undesired components such as fiber, phytate or proteins with antigenic effects. Different feed enzymes such as, carbohydrases, phytases or proteases, can be included in feeds to improve the utilization of energy and nutrients or to degrade several undesired components. Moreover, some enzymes (e.g. amylases, lipases) can be added to the feed of young animals in order to support the endogenous enzyme secretions.

Immune stimulants

Different feed additives may function as stimulator or modulator of immunity processes. Specific cell wall fragments from bacteria or yeasts or sea algae may induce activation of immune cells (e.g. macrophages, lymphocytes).

References

*Domig, K.J. (2005) ''Antibiotikaresistenz und der Einsatz von Antibiotika in der Tierernährung''. 4. BOKU-Symposium Tierernährung: Tierernährung ohne Antibiotische Leistungsförderer. Vienna, Austria: pp. 1–8. * *Kelly, D. and King, T.P. (2001) "Luminal bacteria: regulation of gut function and immunity." In: ''Gut environment of pigs.'' Edited by Piva, A., Bach Knudsen, K.E., Lindberg, J.E.: pp. 113–131. Nottingham University Press, Nottingham, UK. * * * *{{cite journal , last1 = Steiner , first1 = T , year = 2006 , title = The potential benefits of Natural Growth Promoters , journal = Feed Tech , volume = 10 , issue = 2, pages = 26–28 This Article

External links

Possible alternatives to the use of antibiotics as growth promoters. New additivesLessons from the Danish ban of feed-grade antibiotics
Agriculture