The poultry business has experienced unprecedented expansion over the past three

decades and is currently acknowledged as one of the agricultural sector's fastest-growing

subsectors. This has occurred as a result of an increase in the consumption of eggs and meat

due to their accessibility, affordability, and abundance in necessary nutrients that can make

up for dietary deficiencies in important minerals, vitamins, and amino acids (Dhama et al.,

2014a). The genetic potential of the birds, the availability of high-quality feed, the provision

of ideal environmental conditions, and the prevention of disease outbreaks have all benefited

from the utilization of high growth contributing elements. Since this is where most nutrient

intake occurs, intensive research has been done recently on poultry bird gut health in an effort

to increase output (Rinttila & Apajalahti, 2013). Next to the skin, the gastrointestinal system

is the organ most frequently exposed to environmental infections (Yegani & Korver, 2008).

Therefore, maintaining good gut health and function is crucial for poultry production to

ensure proper health and output. The general health and performance of birds will be

hampered due to poor gut function and health, which also affects nutrient digestion and

absorption, ultimately affecting the economics of chicken production. Due to their

widespread availability and low cost, antibiotics are frequently utilized in the production of

by lessening host and pathogen rivalry and minimizing microbial adherence and invasion to

the gut wall, it can preserve the host's vital nutrients. It also reduces the generation of

poisonous amines, which prevents stress in birds. The effect of antibiotics is more obvious in

birds kept in unclean conditions and fed a diet that is relatively low in vitamins and/or amino

acids, which clearly shows the antibiotics' nutrient-sparing effect. The first antibiotic to be

used in veterinary medicine was penicillin G, which was initially made available in 1947 for

intramammary infusions. Since then, regulating animal health in agriculture has become

impossible without the use of antibiotics. Food animals, especially chickens, are given

antibiotics by a variety of ways, including injections, orally in feed, and intravenously in

water. Chlortetracycline, furazolidones, fluroroquinolones, oxytetracycline, sulphonamides,

bacteria is eradicated, leaving only the varieties with peculiar characteristics that are resistant

to the effect. Then, as they proliferate and become the dominating bacteria. Through mutation

or plasmid-mediated transfer, the resistant population so created passes on the genetically

specified resistance to succeeding offspring as well as to other bacterial strains (Catry et al.,

2003). Through the consumption and handling of meat contaminated with these infections,

humans may come into contact with a population of such resistant bacteria (Van den Bogaard

& Stobberingh, 2000). Once acquired, these bacteria can colonize a person's digestive tract

and spread the genes that cause antibiotic resistance to other bacteria in a person's

endogenous microflora, making it more difficult to treat bacterial infections effectively

(Ratcliff, 2000; Stanton, 2013). There has been a major drive to identify alternative treatment

plant extracts (essential oils), among others, are notable substitutes in the production of

poultry (Dhama et al., 2014a). The following are the qualities of alternatives:

Examining potential substitutes for antibiotics as health-promoting drugs for chicken 370

However, more research is required to select probiotic, prebiotic, or synbiotics either

alone or in combination that can result in the selection of strain/s capable of performing

effectively in the gastrointestinal tract. Even combined supplementation of prebiotics and

probiotics, known as synbiotics, is a better strategy for enhancing production. The current

research highlights beneficial antibiotic alternatives for chicken production systems, such as

data used in this study is qualitative data, which is categorized into two types, namely

primary data and secondary data. Sources of data obtained through library research

techniques (library study) which refers to sources available both online and offline such as:

scientific journals, books and news sourced from trusted sources. These sources are collected

based on discussion and linked from one information to another. Data collection techniques

used in this study were observation, interviews and research. This data is analyzed and then

conclusions are drawn.

(Adil et al., 2010). Basically, fatty acids and carboxylic acids with the chemical formula R-

COOH, where R denotes the acids' chain lengths, are included in the category of organic

acids. Short chain length organic acids like formic (C1), acetic (C2), propionic (C3), and

butyric acid (C4) have been used increasingly frequently in poultry feeding. Citric, lactic,

fumaric, malic, and tartaric acids are some more carboxylic acids that are employed (Dibner

& Buttin, 2002). Most organic acids with antimicrobial action have a pKa value (defined as

the pH at which the acid is half dissociated) in the range of 3 to 5. In general, organic acids

are weak acids that are only partially dissociated. Salts of calcium, potassium, or sodium are

also readily available for organic acids. Due to their less volatile nature and solid state, salts

are favoured since they are odorless and simple to handle during the processing of feed.

Additionally, organic acids have a lower potential for corrosion and are more soluble in water

(Huyghebaert et al., 2011). These can be utilized in feed and water. The following are the

suggested successive mechanisms of action for organic acid's bactericidal effects: The initial

acid form of organic acids can pass through the bacterial cell wall. Then, once inside the

bacterial cell, the penetrated organic acids dissociate into the conjugated base form (non-

(Afsharmanesh & Pourreza, 2005; Mroz, 2005). The ability of an organic acid to lower pH in

feed and the GI tract is probably reliant on the GIT's pH circumstances and the pKa values of

the organic acid in question (Kim et al., 2005). The upper portion of the GI tract has a more

noticeable pH reduction. In addition to controlling normal gut flora, application in drinking

water ensures pathogen reduction and subsequently crop (Açkgöz et al. 2011; Hamed &

Hassan 2013). In the closest portion of the gastrointestinal tract, organic acids are easily

absorbed. Due to their capacity to make the gut environment more acidic, intestinal protease

enzyme activity improves, leading to improved nutrition absorption and utilization. This may

be because acidic digestion may be kept in the GI tract for a longer period of time, giving the

GIT more time to digest nutrients (Kidder & Manners, 1978; Mayer, 1994). In addition to

acids are examples of organic acids that are frequently employed to reduce the pathogenic

microbial load, which includes Salmonella and Escherichia coli. Organic acids also lessen

pathogen colonization on the gut wall, protecting epithelial cells from harm. Short chain fatty

acids, when applied daily, enhance the proliferation of epithelial cells, speed up intestinal

healing, improve villous height, and ultimately boost absorption capacity. By breaking

through the phospholipid layer of the bacteria, medium chain fatty acids (MCFA) kill it. They

also change the cell membrane by creating pores that allow contents to flow out (Hermans &

De Laet, 2014). It offers the residing pathogens an early pathogen barrier. Propionic acid

totally inhibits feed mycotoxin and is a powerful mold inhibitor (Zha & Cohen, 2014).

Salmonella Gallinarum counts in crop and caecal contents were lowered when chicks were

peptides (Sunkara et al., 2011; Sunkara et al., 2012). When used in combination, organic

acids cocktail is said to be more effective at preventing the growth of intestinal pathogens

such E. coli and Salmonella than antibiotic growth promoters (Hassan et al., 2010; Hamed &

Hassan, 2013). As potential broad-spectrum inhibitors of metallob-lactamases (MbLs), N-

heterocyclic dicarboxylic acids and pyridyl-mercapto-thiadiazoles can be utilized in concert

with beta lactam antibiotics to combat drug-resistant serotypes (Abdelrahman, 2016).

Oxalic acid, which is found in plant sources, has an impact on the calcium

availability, particularly in chickens that lay eggs. This oxalic acid creates calcium oxalate

salts that are insoluble (Jadhav et al., 2015). The experiments of Tang et al. (2007) that fed

the birds with Lactobacillus strains showed an increase in calcium solubility and availability,

which is linked to its capacity to lower the gut pH because of the generation of lactic and

acetic acids.Organic acids also lessen the likelihood of re-infection and the pathogen

Probiotics are living microbial cultures that are either isolated or combined to help the

host's health (Fuller, 1992). Competition with intestinal receptor sites, formation of particular

metabolites (short organic fatty acids, hydrogen peroxide, and other metabolites with

antimicrobial activity), and immune stimulating effect are all aspects of probiotic bacteria's

mode of action (Madsen et al., 2001; Sherman et al., 2009). Lactobacillus, Streptococcus,

Enterococcus, Bacillus, Clostridium, Bifidobacterium species, and E. coli are among the

microorganisms used as probiotics. Saccharomyces cerevisiae and Aspergillus oryzae are

yeast and fungi used as probiotics (Fuller, 1999). Yeast and bacteria have been added as

living creatures or as spores. Saccharomyces cerevisiae and Bacillus spp. (spores) are

(Witkiewicz et al., 2014). Similarly, feeding Aspergillus awamori (0.05%) increased meat

quality by raising the level of unsaturated fatty acids in broiler chicken breast meat and

improved growth performance by releasing growth promoters (Yamamoto et al.,

2007).Probiotics are used largely to build healthy intestinal flora with the goal of preventing

or lessening the disruptions brought on by enteric pathogens (Dhama et al., 2008). In birds

with serious illnesses, probiotics do not take the place of medicines, but they are helpful in

reestablishing the normal bacterial population. The physiological condition of the bird, the

type and concentration of the probiotic strain, persistence in the intestine, ability to survive

during feed processing and gastrointestinal track, and compatibility with the natural

microbiota of the intestine are all factors that affect the probiotic's effects. The probiotic

1. Enhances gut health by maintaining the desired microbial population equilibrium and

2. Slows the spread of infections and lowers mortality

3. Enhances the effectiveness of feed conversations

4. Enhances body weight increase and growth rate

5. Enhances the digestive enzymes, which helps the body absorb nutrients.

6. Controls lipid metabolism to lower circulating cholesterol levels.

7. Boosts the effectiveness of immunizations

8. Contributes to the quick elimination of mycotoxins

9. Lessen the stress related to traveling, vaccination, temperature, and antibiotic

10. Synthetic vitamins of the B complex

chemicals that prevent pathogen growth. Additionally, they compete with the pathogens for

space in the intestinal epithelium.

Short-chain organic acids (lactic, acetic, and propionic), hydrogen peroxide, and

bacteriocins, such as nisin, acidolina, lacocydyna, lacatcyna, reutryna, entrocine, and

laktoline, are all products of probiotic bacteria. Probiotic-produced bacteriocins have a strong

antibacterial effect against Clostridium perfringens, Salmonella, Campylobacter, and

Escherichia coli. According to Mahmood et al. (2014), supplementing feed with probiotics

may be a candidate technique for reducing oocysts and necrotic enteritis as well as Eimeria

acervulina and E. tenella (Lee et al., 2007). Probiotics also work by stimulating the immune

system because of their capacity to adhere to the intestinal mucosa, which enables them to

promotion (Blanch, 2015). The in ovo injection of probiotic culture is a new method of

probiotics feeding, particularly in chicken. The newly hatched chick will have a sterile

gastrointestinal tract, therefore it will harbor the microflora when it enters its raising home

system and is exposed to diverse environmental bacteria. Although colonization occurs in

chicks after hatching (Amit Romach et al., 2004), Pedroso (2009) and Bohorquez reported

finding a small number of microorganisms in the prenatal stage of the birds' development

(2010). Probiotics are fed to birds, and studies have shown that this reduces the effects of

numerous stressors. The newly hatched chicks are similarly subjected to several challenges,

including hatching, sexing immunization, dehydration, malnutrition, transit, etc. Numerous in

ovo injection experiments have demonstrated that providing necessary amino acids, minerals,

Prebiotics are nondigestible feed additives that assist the host by favorably enhancing

the growth rate and/or multiplying a small number of beneficial bacteria in the host's colon to

improve gut health. These provide food for the beneficial microorganisms in the stomach.

According to Cummings and Macfarlane (2002), the primary functions of prebiotics are

altering the GI microflora, stimulating the immune system, preventing colon cancer and

reducing pathogen invasion, reducing cholesterol and odor compounds, enhancing gut health

by promoting enzyme reactions, reducing ammonia and phenol products, and ultimately

reducing production costs (Ghiyasiet al., 2007; Khksar et al., 2008; Peric et al., 2009). The

primary prebiotics evaluated in chickens include gluco-oligosaccharides (GOS), fructo-

oligosaccharides (FOS), mannan-oligosaccharides (MOS), stachyose, and oligochitosan

(Jiang et al., 2006). It should not be hydrolyzed or absorbed in the upper gastrointestinal tract;

counts in the meat and coccus. In addition, prebiotics promote the growth of Lactobacillus

and Bifidobacteria and reduce the incidence of harmful gut infections (Dhama et al., 2007)

Therefore, prebiotics can be utilized as an alternative to antibiotics to enhance the health and

performance of chickens by altering the population of gut microorganisms and boosting the

immune system by lowering infections. Additionally, additional research is required to

comprehend the specific function and mechanism of action of a single component or

combination of components. The bacteria of the hens' gastrointestinal tract influence both

their immunity and growth. Prebiotics are renowned for their capacity to encourage the

growth of beneficial bacteria (Gibson, 1999; Van Loo et al., 1999), but they also modify the

innate immune response by interacting with receptors, boosting endocytosis, and activating

The probiotic and prebiotic mixture, or synbiotics, gives the living culture and feeds

them so they have a higher chance of surviving in the bird's intestinal system (Yang et al.,

2009; Gaggia et al., 2010). The most well-known synbiotic pro-prebiotic combos are lactitol

and lactobacilli, and fructo-oligosaccharides and bifidobacteria (Yang et al., 2009). Intestinal

microflora play a significant role in bird health, and if the equilibrium between beneficial

microbes is upset, the bird's health and general performance will suffer. This encourages

researchers to investigate the impact of dietary supplements in the form of prebiotics, which

can be used to boost the establishment of beneficial bacteria and improve poultry bird

production. Synbiotics are prebiotics that are supplemented to ensure the growth of probiotics

(Awad et al., 2008; Hassanpour et al., 2013). The best synbiotic effects for chickens have

only been revealed in a small number of research (Li et al., 2008). Finding the ideal probiotic

and prebiotic ratio and evaluating how well they work together as potential synbiotics must

be given careful consideration in order to maintain good health. According to a study by

Madej et al. (2015) in broilers, the development of numerous immune organs was affected

when inulin (a prebiotic) and Lactobacillus bacteria were administered in utero.

It has been demonstrated via the development of broilers that the use of minerals and

various vitamins can improve the health condition of poultry. The bad health status of birds

has increased due to mineral and vitamin supplementation, increasing the farm's cost-benefit

ratio (Prescott & Baggot, 1993; Peric et al., 2009). There are many positive effects, including

guinea pigs or humans (Lin et al., 2006; Khan, 2011). Although vitamin C does not have a

suggested dose for birds, its antioxidant properties may help to reduce stress. According to a

study, broilers fed vitamin C performed well even when exposed to various environmental

stresses (McKee & Harrison, 1995). By keeping minerals, particularly iron, in the reduced

ferrous state, vitamin C facilitates the absorption of minerals and plays a significant role in

the metabolism of amino acids (McDowell, 1989). L-arginine supplementation and vitamin C

administration have improved broiler meat quality. The feed conversion ratio and growth

performance in chicken were both boosted by a different vitamin, vitamin E. The

recommended dose of vitamin E for a bird is 5 to 25 IU/kg of feed, while larger doses have

also improved poultry performance (NRC, 1994). Iron plays a growth-promoting and -

stressors. Broilers fed a high-energy diet showed an increase in feed efficiency, according to

Gopi (2013). Additionally, consumption of the chemical strengthens their lipophilic systems'

antioxidant defenses. Through increased energy availability, vitamin Q consumption

strengthens the host's defense against different microorganisms, including bacteria, viruses,

protozoa, and bacteria (Bliznakov, 1978; Hogenauer, 1981). Both Folkers et al. (1982) and

Gopi (2013) noted an increase in broiler haemeagglutination titer (HI) against the Newcastle

disease virus and immunoglobulin G production.

Phytochemicals, also referred to as phytobiotics, are substances originating from

health-promoting compounds is evolving globally (Narimani-Rad et al., 2011). Since its anti-

microbial activity has been discovered in various types of organisms (Brut, 2004; Murali et

al., 2012), (both gram positive and gram negative organisms). They are mostly utilized as an

alternative antibiotic growth promoter in monogastric (poultry and pig) animal production

(Khaksar et al., 2012; Karangiya et al., 2016). They have been reported to favorably change

the gut microflora by less harmful organisms, while the particular mechanism of action is still

unknown (Salim, 2011). The change in membrane permeability to hydrogen ions (H+) is the

most likely mechanism of action. It exhibits antibacterial, antiviral, anti-fungal, and anti-

protozoan properties in addition to its antibacterial properties. Their anti-fungal properties are

becoming more significant as a result of these compounds' use in environmentally friendly

and cost-effective fungicide preparations, as well as in fly-repelling products (Afzal et al.,

2010). (Mansour et al., 2011).

stress, due to their antioxidant action (Wei & Shibamoto, 2007). Their antioxidant properties

may be useful in enhancing the shelf life of processed meats and minimizing the loss of

muscle during the thawing of cold-stored goods (Windisch et al., 2008). These chemicals

from plants have characteristic flavors that could be used in diets for humans and pigs. These

substances draw customers and enhance ingestion. Currently, essential oils are utilized to

make ice cream and other things. They still have some controversy about their use as a

flavoring component in poultry production. The body's digestive process is accelerated by the

dietary addition of active ingredients or the source of such ingredients. They were discovered

to enhance the release of digestive enzymes from the pancreas and liver, specifically trypsin,

amylase, and bile (Gopi et al., 2014a). This will contribute to increased feed efficiency and

liver's production of cholesterol (Lee et al., 2004). Utilizing this phenomenon might enable

the production of meat and eggs with minimal cholesterol levels (Mohamed et al., 2012).

Despite the fact that these substances are generally acknowledged as safe (GRAS), their

degree of use is still under question because of the unidentified mechanisms behind their

range of activity and the potential for bodily implantation.

Herbal medicine has gained popularity recently primarily as a result of its advantages

over chemical medications, which include reduced or nil toxicity, availability in nature, and

appropriate feed additive properties (Khan et al., 2010; Khan et al., 2012a). It is well known

that plant components like herbs and spices have antibacterial properties (Nychas &

Skandamis, 2003). Essential oils in particular are items made from plant parts that are known

bulbs, parsley seeds, fruits, rhizomes, leaves, basil, and tea plants (Nychas & Skandamis,

2003). Examples of substances with strong antibacterial properties are cinnamon barks with

high quantities of cinnamamic aldehyde and spices with high levels of eugenol (Davidson &

Naidu, 2000). According to reports, essential oils from plants have a broad antibacterial