Dr. Rambabu. D, Associate ProfessorDept. of Poultry Science, College of Veterinary Science, Korutla
PV Narsimha Rao Telangana Veterinary University
The cost of feeding poultry accounts for around 75% of the overall cost of production and is a crucial instrument for maximizing the genetic potential of the bird because it provides all the essential nutrients for good growth and health. However, certain pathogenic organisms, such as E. coli, Salmonella, etc., might potentially enter the gastrointestinal tract (GIT) or gut through feed. The health of the GIT is crucial for poultry production to reach its full potential and output. As a result, several performance additives are used to supplement the bird’s diet with a balanced, sanitary diet and to maximize nutrient absorption. A healthy GIT influences not just nutrition absorption, metabolism, and feed digestion, but also immune response, illness resistance, and the use of protein and energy. Given that poor gut health impairs immunity and production, feeding birds suitable, sanitary food free of possible pathogens is thought to have a positive impact on their digestive systems.
Antibiotic growth promoters (AGPs) have been used largely for many years to maintain optimal gut health and to lessen the impacts of feed borne infections that affect gut health. However, the poultry business has found a means to replace antibiotics with probiotics, prebiotics, essential oils, etc. as a result of greater public awareness regarding the development of cross resistance of infections to antibiotics. However, in recent years, there has been a renewed emphasis on the use of organic acids in chicken feed to preserve optimal gut health, enhance nutrient absorption, and boost growth performance. For more than 50 years, they have been used to decrease bacterial development and mould in feedstuffs and so maintain the hygienic quality of feed. Organic acids and their salts, on the other hand, not only aid in the preservation of feed and silages but also work to lower bacterial content and retain the nutritional value of feed because of their antibacterial action. This ensures animal performance and enhances nutrient digestibility, both of which contribute to stable animal health. In addition to enhancing feed hygiene, investigations have shown that organic acids stabilise the gut microflora eubiosis and their effects on feed digestion and absorption. In animal husbandry, cheaper feed costs and shorter times to market weight are made possible by decreased feed conversion rates, increased daily weight growth, and decreased frequency of diarrhoea. There are several ways to introduce organic acids to animal feed, including adding them directly or through special premixtures. Liquid acids and blends can be sprayed on the feed. Solid acids and acid salts can also be added. Drinking water may potentially contain organic acids.
Fatty acids and amino acids are examples of organic acids, which are commonly defined as any organic carboxylic acid having the general formula R-COOH. Formic, acetic, propionic, and butyric acids are examples of simple monocarboxylic acids. Lactic, malic, tartaric, and citric acids are examples of carboxylic acids having a hydroxyl group, typically on the -carbon. These weak acids are believed to have the ability to enhance growth performance, nutritional utilisation, and health when introduced to the feed in sub-therapeutical dosages. Additionally, not all organic acids affect the gut microbiota since they are partially dissociated. The majority of organic acids having antibacterial action have pKa values in the range of 3 to 5.
MODE OF ACTION
The ability of organic acids to lower intestinal pH and cause changes to the intestinal ecology are closely tied to their postulated method of action. Organic acid supplements primarily aim to reduce intestinal pH in order to minimise microbial colonisation and growth, which reduces nutritional competition. Through pH decrease, anion & proton actions in microbial cell, and other mechanisms, organic acids and their salts have the ability to impede the growth of stomach and gut bacteria. Through the semi-permeable barrier of the bacterial cell wall, organic acids in an undissociated (non-ionized, more lipophilic) state can enter and enter the cytoplasm. The undissociated organic acid molecules separate at the internal pH of bacteria (7.0), producing protons(H+) and anions (A-). Bacteria’s internal pH decreases as a result of this. A significant difference between the internal and external pH cannot be tolerated by bacteria that are pH sensitive. The pH inside the bacterium is brought back to normal by a particular H+ – ATPase pump. Decarboxylases and catalases, for example, are inhibited by lowering pH, as is glycolysis and active protein synthesis by the bacterium. By causing an anionic imbalance and internal osmotic issues for bacteria, the anionic (A-) component of the acid that is confined inside the bacterial cell, can permeate easily through the cell wall in its non-dissociated state, turns poisonous. The composition of the organism’s cell wall or outer membrane can explain differences in the antibacterial spectrum of different organic acids. Since bacteria’s cell walls are less complicated than those of moulds, the lipophilic property of some organic acids, such as propionic acid, makes entry easier than it would be with formic acid, which can pass through bacteria and is more bacteriostatic than the other organic acids. Because different classes of microorganism have differing susceptibility to various organic acids, it is necessary to use mixtures of organic acids and salts to be more effective against a wider range of microbial species than single acids. Organic acids have an antibacterial effect on the feed by lowering the pH, which also reduces the buffering capacity of the feed, an essential component for efficient enzyme activity and microbial proliferation control.
There are four general categories into which the function of organic acids in poultry nutrition can be divided:
1. EFFECT ON PERFORMANCE
Organic acids can be used as effective substitutes for antibiotics in poultry feed and have specific growth-promoting effects. Numerous researchers found that adding one or more organic acids to feed significantly increased broiler growth, average daily gain, and feed conversion. According to a report, adding lactic acid, citric acid, ascorbic acid, propionic acid, and benzoic acid to diets significantly improves broiler chickens’ growth and performance (P 0.05). Better growth performance is due to decreased colonisation of pathogenic bacteria in the gastrointestinal tract (GIT), decreased competition for nutrients between the host and exogenous pathogen microflora, decreased buffering capacity due to their direct antimicrobial effects, and increased nutrient digestibility.
2. IMPACT ON DIGESTION AND USE OF NUTRIENTS
Organic acids have been reported to be a viable alternative to enhance nutrient utilisation and digestibility in addition to enabling and maintaining feed hygiene. Crude protein (CP), ether extract, and nitrogen free extract of broiler diets have been shown to have higher metabolizable energy (ME) and nutritional digestibility when organic acids like acetic acid and fumaric acid are included in the diet. The retention of dry matter, crude protein, and neutral detergent fibre increased with the addition of 2% citric acid to the broiler feed. This increase in the digestibility of CP and ME was ascribed to a decrease in microbial host competition for nutrients, endogenous nitrogen losses, and ammonia generation. Additionally, organic acids increased stomach proteolysis and enhanced the absorption of protein and amino acids. Slower rate of food transit into the digestive tract and improved nutritional absorption were two benefits of organic acids on digestion. Protein is more easily digestible because organic acids lower the pH of intestinal ingesta. Organic acids play a key effect in limiting the colonisation of enteropathogenic bacteria, which are sensitive to acidic pH, as well as favouring the stimulation of the growth of good bacteria like Lactobacilli. The decline in those acid-intolerant microorganisms could indirectly promote an increase in nutrient digestibility.
The utilisation of phytate phosphorus can be increased and the mineral digestibility can be improved by adding dietary organic acids to poultry diets. Supplementing the broiler food with a combination of organic acids increased nutritional availability and digestibility (such as calcium and phosphorous). Increased mineral element retention and bone mineralization are the outcomes of the digestive tract’s growing favourable microbiota (Lactobacillus spp.). Fumaric acid was added to the diet, which improved the balance of calcium and phosphorus by 14% and 13%, respectively.
3. GASTROINTESTINAL TRACT IMPACT
In the chicken industry, having ideal intestinal health is crucial to achieving target growth rates and the highest possible feed efficiency. Organic acid supplementation has a positive effect on gut histomorphology in addition to having a positive impact on growth performance and nutrient digestibility. According to studies, adding organic acids to the meal greatly enhances the villus breadth, height, and area of the duodenum, jejunum, and ileum in broiler chickens. All small intestinal segments’ muscularis thicknesses are reduced as a result of organic acids. Since the thickening of the mucous layer on the intestinal mucosa contributes to decreased digestive efficiency and nutrient absorption, this aids in enhancing the digestion and absorption of nutrients. Organic acids lessen intestinal colonisation and infectious processes, which leads to a reduction in intestinal mucosal inflammation and an improvement in villus height and function for secretion, digesting, and nutritional absorption. The decrease in pathogenic organisms, which can damage the villi and crypt structure by producing toxins, also contributes to the explanation for the improvement in intestinal gut structure. Organic acids have a positive impact on the microbial population of the gut in addition to the influence on gut architecture. Sub-therapeutic doses of organic acids reduce the adhesion of bacteria such Escherichia coli, Campylobacter, Clostridium perfringens, Salmonella kedougou, and Salmonella gallinarum, which in turn modifies the natural microbial community in the gut. Following the addition of organic acids (benzoic and fumaric acid) to their feeds, broiler chickens had a dramatically reduced population of coliform bacteria in their guts.
4. IMPACT ON IMMUNITY
Various studies have demonstrated that organic acids could help in the promotion of natural immune response in chicken resulting in greater antibody titers against infectious bursal disease (IBD) and newcastle disease (ND) (ND). This can be explained by the potential that boosting the activity of the hexose monophosphate pathway will hasten the differentiation of lymphoid organs and, as a result, increase the levels of circulating antibodies. The rapid elicitation of an immune response is indicated by the considerable rise in CD4 and TCR-II cells after the administration of organic acid. Additionally, it has been noted that birds fed an organic-acid diet had thicker thymus and bursa of fabricius immunological organs as well as a larger amount of blood globulin. It has been hypothesised that the enhanced lymphocyte density in lymphoid organs and the inhibitory effects of organic acids on pathogens in the gastrointestinal system may be responsible for the improvement in bird immunity.
As a result, adding organic acids to chicken diets improves bird performance in addition to feed hygiene by lowering the pathogen burden. This effect is broad, affecting everything from increased immunity and general productivity to improved gut health in terms of both morphology and microbial balance. As a result, organic acids can be thought of as a practical and significant replacement for AGPs in chicken feed.