USE OF EUBIOTICS AS ALTERNATIVE TO ANTIBIOTIC GROWH PROMOTERS ( AGPs) IN ANIMAL NUTRITION
As the routine use of antibiotics is no longer accepted, the term ‘eubiosis’ has made its entry. It is a completely new way of approaching animal health: from fighting the microflora with antibiotics, towards supporting and cooperating with the favourable microflora. Eubiosis refers to an optimal balance of the microflora of the gastrointestinal tract. It is one of the key factors for optimal animal performance. Feed additives can be a very helpful tool to promote eubiosis and to overcome an imbalance in the microflora of the gastrointestinal tract, also known as ‘dysbiosis’. The strategy which combines nutritional knowledge with the use of different modern non-antibiotic feed additives is defined as ‘eubiotic nutrition.
‘Eubiotics’, which is related to the Greek term ‘Eubiosis’, referring to an optimal balance of microflora in the gastrointestinal tract. The main purpose of using such eubiotics is to maintain the intestinal eubiosis, which will result in an improved health status and performance in farm animals.
In modern Livestock farming , antibiotics have been routinely used as growth promoters in animal feeding. Consequently, the widespread application of antibiotic growth promoters has strongly contributed to the development of resistant bacteria. Since the 1940’s antibiotic growth promoters (AGPs) are an integral part of livestock production. The industrialisation of livestock farming first saw the introduction of antibiotics in animal feed for poultry in the 1940’s.
Nevertheless, the rise to prominence of AGPs in the animal industry came with its own share of criticism and controversy. The use of feed antibiotics became increasingly contentious, especially following the release of the Swann committee report in United Kingdom in 1969. The committee was set up following reports of transferable oxy tetracycline resistance from food animals to humans. The intensive use of antibiotics in animal husbandry, suggested the Swann report, had led to a surge in the rates of antibiotic-resistant bacteria. It called for restrictions to be put in place to minimise the risk of resistance.
The growing awareness surrounding the risks of feed antibiotics, lead to the introduction of a range of new measures by the EU to ensure food safety. In 2006, Europe enacted a total ban on the use of AGPs in animal feed, and restricted the use of antibiotics in animals to health reasons with a veterinary prescription.
Nutritional strategies have the potential to overcome and alleviate the challenges posed by AGPs, and substitute feed antibiotics employed to improve animal growth rates.
Alternatives for AGPs are only of practical significance when they improve animal performance at levels comparable to AGPs. Microbiota modulating and immunomodulatory compounds have potential and are used as feedstuff of feed additives. Enzymes, acids, per- and probiotics and herbs or etheric oils are some examples of product classes which are used as alternatives for AGPs. Within each product class, numerous products are on the market, and while some products clearly have potential, for others the efficacy is not clear.
Criteria for Alternatives to Antibiotics (AGPs)
- Prevent pathogens – Clostridium perfringens
- Positive event on commensals
- Anti-inflammatory effect and intestinal wall vitality
- Compatibility with commonly used feed additives and feed pellet stability
- No resistance issues and no withdrawal periods
- Improvement in animal performances – FCR body weight, and low mortality
Following are the additive compound may be used as Alternatives to Antibiotics (AGPs)
Acidifiers ———
Acids such as formic, fumaric, lactic, propionic, citric, sorbic and phosphoric have been studied for potential growth promoting properties. Ravidran and Kornegay (1993) reviewed the literature and came to the conclusion that
although benefits were observed in many studies, results were inconsistent. Acidifiers may work by supplying
energy to the animal or have a function similar to other antimicrobial substances. Acidifier combinations and
enterically protected acidifiers hold promise of more consistent performance. Food grade acidifiers are generally recognized as safe, do not require approval and have no concern over safety.
Probiotics —————
Products based on Lactobacillus, Bacillus,Saccharomyces and many other organisms are marketed for use as growth
promotants. Their response has been somewhat inconsistent in the past possibly due to loss of viability in the feed or
destruction during passage into the intestinal tract. Newer products and delivery systems are being developed to
improve efficacy. Of particular interest is the concept of inoculating baby chicks in the hatchery with probiotics. A
new product developed by the U.S.D.A. called CF-3 is based on a stable culture of 29 anaerobic bacteria. This
product shows promise in protecting birds from Salmonella and may also promote growth (Burns, 1995).
Prebiotics —-
Prebiotics can be defined as non-digestible feed ingredients with selective effects on the intestinal microbiota. Oligosaccharides are the main components and the range is diverse and may be based on any of the hexose monosaccharides, including glucose, fructose, galactose and mannose (Durst, 1996) with a polymerisation degree of between 2 and 20 monosaccharides. Grain legumes are the most common natural sources of oligosaccharides, being present as raffinose, stachyose and verbascose. ‘Synthetic’ oligosaccharides are derived from the direct polymerisation of disaccharides or from the fractionation of both vegetable and microbial cells. Oligosaccharides such as 308 arabinogalactose, arabinoxylan and rhamnogalacturonose are derived from polysaccharides of 309 soybean (with about 3-5% galacto-oligosaccharides), wheat and fruit, respectively.
Enzymes —————–
Feed enzyme supplements are protein catalysts derived from various microorganisms that enhance digestion of feed ingredients. Enzymes enhance growth by degrading deleterious substances in the feed such as poorly digested
polysaccharides or antigenic proteins. They also aid digestion of nutrients. The science of enzyme use in feed is developing rapidly with many successful products already developed.
Microflora enhancers —————–
Fermentation residues containing Aspergillus meal and killed yeast have been used as growth promotants since the
early 1980’s. These products contain bacterial growth factors that stimulate growth of beneficial intestinal bacteria
such as Lactobacillus in the gut of the animal. Many studies have reported effects similar to those observed with
antibiotics.
Immunomodulators —————
These are compounds that modulate and/or selectively stimulate immune response. The idea is to prevent immune
stress to antigens in the gut, yet still allow immunity to develop when required. Certain polysaccharides such as
glucans, peptidoglycans (muramyl peptide), mannanoligosaccharides and fructo-oligosaccharides are currently being
sold as immune stimulators. These products are derived from the cell walls of yeasts and other organisms such as
Brevibacterium lactofermentum. Microbial glucans have linkages in the b-1,3 and b-1,6 positions unlike the b-1,4
linkages found in barley glucans. Peptidoglycan was found to enhance NO2 release from macrophages thus
enhancing viral and bacterial killing capacity. Both mannanoligosaccharides and yeast glucans have been reported to
improve phagocytic function of neutrophils and monocytes. b-glucan has been found effective in enhancing performance and reducing piglet morbidity, mortality and diarrhea caused by Streptococcus suis (Dritz et al., 1995). Trial work in broilers with mannanoligosaccharide has also shown significant improvement in performance (2.5% FCR) and reduced mortality (Macdonald, 1995). Conjugated linoleic acid (CLA) is a compound that has been recently shown to reduce negative effect of cytokines in animals undergoing immune stress. Growth depression of chicks from injection of E. coli endotoxin was eliminated with the addition of 0.5% CLA to feed (Cook et al.,1993). The addition of CLA had no effect on immune response against sheep red blood cells indicating that immune stress may be reduced while still main-taining immune function.
Carotenoids ————–
Growth promoting, immune stimulating and reproduction enhancing effects of carotenoids have been recently reported by several authors (Inborr and Foder, 1996; Chew, 1993; Cafantaris and Papadopoulos, 1995). Dietary inclusion of astaxanthin at two ppm has been reported to improve weight gain by 5% and FCR by 2% in 36 day old market broilers. Carotenoids have also been reported to stimulate phagocytic and bacteria killing ability of blood neutrophils and peritoneal macrophages. Beta carotene in combination with vitamin E, biotin, folic acid and vitamin C was shown to improve reproductive performance in swine by 0.5 piglets per sow per year.
Herbal products ———–
Plant derived agents including saponins, alkaloids, esters, quinones, isobutylamides, phenol carboxylic acid esters and terpenoids are currently being studied for growth promoting and immune modulating effects (Hylands and Poulev, 1995). Herbal products used to promote growth in poultry are currently quite popular in India and China (Devegowda, 1996). In many cases, only the manufacturer knows the composition and potency of these products. Although marketed as “natural”, some of these products may be highly pharmacolo-gically active or even carcinogenic. As such, herbal products should be required to undergo the same scrutiny for efficacy and safety testing as other additives before being allowed to enter the human food chain.
Metabolic peptides —————
Peptides that regulate intestinal absorption are currently under intense study (Croom et al., 1996). Agents such as epidermal growth factor and pancreatic polypeptide YY have been found to enhance glucose and amino acid absorption when applied into the lumen of the gut. These peptides appear to function by increasing the number of “nutrient transporters” present in mucosal cell membranes. If these substances can be produced at economical cost, and practical methods can be found to deliver them from feed to intestinal cells without destruction, they may represent a new class of safe and efficient growth promotants.
ß-agonists ——————
These compounds have been extensively studied for their ability to promote growth, enhance feed efficiency and
repartition nutrients toward protein and away from fat synthesis. Compounds such as clenbuterol, cimaterol and
ractopamine are norepinephrine analogs. These stimulate b-adrenergic receptors in tissue causing a host of different metabolic changes in animals. Such products are manufactured commercially for use in human medicines including bronchodilator sprays for asthmatics. None of these products have been approved in the U.S., Australia, Japan, or E.E.C. for use as feed additives because of concerns over animal health and tissue residues. Commercial use has occurred in smaller and less regulated countries to the benefit of swine producers but not the meat consuming public.
Worldwide pressure for the elimination of antibiotics in animal production has stimulated the search for new solutions. Eubiotics offer a different way of managing gut health in livestock. The effectiveness of these new approaches tends to be evaluated against the results produced during decades of antibiotic use.
It is therefore necessary to re-educate producers who are familiar with the ‘antibiotic era’. Animal production will long continue to depend on the use of traditional molecules, but eubiotics and other technologies offer effective alternatives and/or complementary approaches. No standard model exists for the use of eubiotics, and for each challenge and interacting factor, it is necessary to conceive and implement prevention programs that are practical, enjoy good benefit-cost ratio, and are suitable for the specific circumstances in which they are to be applied.
Dr. Rajesh kr. Singh, & Dr. Surinder khanna.
Reference-On request
