**1. Introduction**

Broiler chicken is an affordable and complete source of protein for human consumption. In addition, it is a source of income for families, small and large companies around the world [1, 2]. In broiler breeding, intestinal health is crucial, due to its influence on health and use of nutrients [3]. Furthermore, its influence directly in obtention of the ideal performance parameters. Special attention must be paid to the gastrointestinal tract, as it is where most disease-causing pathogens enter, settle and multiply [4]. In the same way preventing or treating diseases of the tract results in more efficiency for other bird body systems [5].

After hatching, the intestinal tract of birds is sterile, which becomes populated with microorganisms when searching for food, constituting their intestinal flora [3]. Intensive breeding coupled with confinement applied in modern production of broilers limits the movement of birds putting them at risk of health vulnerability and dependence on the provided diet [6].

Various additives with different functions have been used to formulate complete diets for broilers. Some additives act as nutrition increments' and others guarantee protection against disease. Antibiotics were among the most used additives to control the birds health [7].

Antibiotics were widely used as growth promoters, whose application was made in sub-therapeutic doses throughout the breeding of broilers. However, strong evidence indicated that antibiotics contributed to the development of resistance in pathogenic strains [8, 9].

The emergence of resistant strains in poultry farms have been rousing a major concern. Reports have proven not only the damage on the animal's health but also to human due to the trophic interactions [9, 10]. Consequently, there are major concern to withdraw antibiotics from broiler chickens. The search of alternative sources of additives that would be potential substitutes for antibiotics in broiler chickens become a crucial issue for many researchers [11]. Nonetheless, the use of antibiotics presents economical concerns, because beside to aforementioned advantages they acted in the control of diseases and in reducing the burden of carcass contaminants [12].

Probiotics became a potential antibiotic substitute additive in broilers, due to its influence in performance of broilers and security compared to antibiotics [13]. Probiotics are groups of non-pathogenic microorganisms, normally inhabitants of the intestinal flora, which, when administered have the benefit of balancing the intestinal microbiota by inhibiting the excessive multiplication of pathogenic microorganisms [3]. In addition, the presence of these in the tract activates the host's immune system, stimulating them to remain alert against any invasion [14].

Probiotics had already been applied to humans and other animal species. Certain species of microorganisms among which bacteria, fungi, and yeasts are carefully selected to be used as probiotics [15].

In broiler, however, even today, it is still not possible to accurately predict the effect of probiotics, due to several intrinsic and extrinsic factors that interfere with their use and results tend to be different between studies. The purpose of this study is to critically analyze the main findings regarding to probiotics applications in broilers.

#### **2. Probiotics in broilers, concept, types and effect**

Probiotics in animals as well as in humans are being extensively studied, due to its effect on the restoration of the intestinal microbiota, reversal of dysbiosis (gastrointestinal imbalance), and safety in its use [16, 17]. The use of antibiotics is banned from the European Union (EU) and other parts of the world, catalyzed the research of probiotics for broilers. In addition, the antibiotics ban, not only affected countries importing meat but also pressured the meat exporting countries to meet the regulations of receipt countries [10, 18].

The use of antibiotics in animals is prohibited in the EU and the USA, is the practice responsible for creating antibiotic-resistant bacteria, known as superbugs. These superbugs having animals as reservoirs can spread among other animals, management personnel, food and the environment [12].

Some portfolios have been developed possible alternatives to antibiotics [11], these have included probiotics in the most advanced approaches to serve as preventive, and alternative therapies with potential uses in animal health. Derived from Greek, the word probiotic means "pro-life" and in the search to cover the correct mechanism of probiotics, this term has undergone several changes over the years. In animal production, it can be summed up as a "feed supplement for live microorganisms that beneficially affects animal flora by improving the microbial balance in the intestine" and should be viable and stable in the different breeding conditions [19].

**147**

**Table 1.**

*Probiotics as a Promising Additive in Broiler Feed: Advances and Limitations*

The most used microorganisms as feed supplements are mainly bacteria, mostly from the group of Gram-positive *Bifidobacterium* and lactic acid bacteria (LAB). The genus *Enterococcus, Lactobacillus, Pediococcus, Streptococcus, Lactococcus*, and *Leuconostocos,* and also *Bacillus* are the most used. In addition to bacteria, fungi and yeast strains, mainly from the species of *Saccharomyces cerevisiae* and *kluyveromyces* are also used as probiotics [8, 19, 20]. A microorganism to be considered as a probiotic must meet some requirements: (1) to resist and quickly occupy the intestinal tract; (2) be part of the intestinal habitat; (3) survive the action of digestive enzymes; show antagonistic action against pathogenic microorganisms;(4) be non-toxic and non-pathogenic; (5) be stable and viable in commercial preparation

Several probiotic strains are included in poultry diets to promote animal growth and health, especially when conditions are challenging for health. Several studies have reported the beneficial effects of probiotics on various aspects of bird health. Furthermore, parameters related to supplementation with probiotics in diets increased body weight gain, feed intake and improved feed conversion rate in birds,

Until now, many mechanisms about the action were proposed. However, the main mechanisms of action of the probiotics are competition for binding sites, where the probiotics adhere to the intestinal epithelium wall, hindering competition and the joining of pathogenic microorganisms, this higher concentration of the beneficial microbiota also causes it to have advantage in competition for nutrients [12]. Supplementation with *Bacillus subtilis* improves the performance and immunity of broilers reared in warm conditions, and birds fed probiotic in the diet were able to deal more effectively with heat stress through immunity modulated by the

**Parameters evaluated Probiotic strains used Source/Author**

Performance in broilers *Bacillus coagulans* and *Lactobacillus* sp. [24] Use of nutrients *Buttiauxella* sp. and *Bacillus* sp. [25]

*termophilus*

*bifidum*

Resistance to heat stress *Bacillus subtilis* [32]

Immune performance and protection *Lactobacillus acidophilus, L. casei,* 

Hatching of fertile eggs *Lactobacillus acidophilus; Bacillus subtilis*

Microbial profile of cecum and litter *Bacillus subtilis, Bacillus pumilus* and

*Lactobacillus plantarum* 16 and *Paenibacillus polymyxa* 10

and *Clostridium butyricum*

and *Bifidobacterium animalis*

*Bacillus megaterium* (spores*)*

*Lactobacillus acidophilus, L. casei; Enterococos* and B*ifidobacterium* 

*Lactobacillus acidophilus; Bacillus subtilis*

*Enterococos faecium* and *Bifidobacterium* 

Multiceps *of Bacillus* [29]

*Bacillus amiloliquofaciences* H57 [22]

[23]

[26]

[27]

[28]

[30]

[31]

*DOI: http://dx.doi.org/10.5772/intechopen.97957*

and stimulate the immune system [21].

were also reported (**Table 1**).

Promotion of feeding efficiency and improvement of subclinical necrotic

Intestinal barrier, antioxidant capacity, apoptosis and immune response

Performance, apparent ileal digestibility, blood and excreta characteristics

Improving the stress of stocking density,

Energy digestibility, performance, disappearance of non-starch

*Most evaluated parameters in broiler probiotics uses.*

enteritis

yield

polysaccharides

*Probiotics as a Promising Additive in Broiler Feed: Advances and Limitations DOI: http://dx.doi.org/10.5772/intechopen.97957*

*Advances in Poultry Nutrition Research*

control the birds health [7].

pathogenic strains [8, 9].

selected to be used as probiotics [15].

**2. Probiotics in broilers, concept, types and effect**

management personnel, food and the environment [12].

the regulations of receipt countries [10, 18].

Various additives with different functions have been used to formulate complete diets for broilers. Some additives act as nutrition increments' and others guarantee protection against disease. Antibiotics were among the most used additives to

Antibiotics were widely used as growth promoters, whose application was made

in sub-therapeutic doses throughout the breeding of broilers. However, strong evidence indicated that antibiotics contributed to the development of resistance in

control of diseases and in reducing the burden of carcass contaminants [12].

The emergence of resistant strains in poultry farms have been rousing a major concern. Reports have proven not only the damage on the animal's health but also to human due to the trophic interactions [9, 10]. Consequently, there are major concern to withdraw antibiotics from broiler chickens. The search of alternative sources of additives that would be potential substitutes for antibiotics in broiler chickens become a crucial issue for many researchers [11]. Nonetheless, the use of antibiotics presents economical concerns, because beside to aforementioned advantages they acted in the

Probiotics became a potential antibiotic substitute additive in broilers, due to its influence in performance of broilers and security compared to antibiotics [13]. Probiotics are groups of non-pathogenic microorganisms, normally inhabitants of the intestinal flora, which, when administered have the benefit of balancing the intestinal microbiota by inhibiting the excessive multiplication of pathogenic microorganisms [3]. In addition, the presence of these in the tract activates the host's immune system, stimulating them to remain alert against any invasion [14]. Probiotics had already been applied to humans and other animal species. Certain species of microorganisms among which bacteria, fungi, and yeasts are carefully

In broiler, however, even today, it is still not possible to accurately predict the effect of probiotics, due to several intrinsic and extrinsic factors that interfere with their use and results tend to be different between studies. The purpose of this study is to critically analyze the main findings regarding to probiotics applications in broilers.

Probiotics in animals as well as in humans are being extensively studied, due to its effect on the restoration of the intestinal microbiota, reversal of dysbiosis (gastrointestinal imbalance), and safety in its use [16, 17]. The use of antibiotics is banned from the European Union (EU) and other parts of the world, catalyzed the research of probiotics for broilers. In addition, the antibiotics ban, not only affected countries importing meat but also pressured the meat exporting countries to meet

The use of antibiotics in animals is prohibited in the EU and the USA, is the practice responsible for creating antibiotic-resistant bacteria, known as superbugs. These superbugs having animals as reservoirs can spread among other animals,

Some portfolios have been developed possible alternatives to antibiotics [11], these have included probiotics in the most advanced approaches to serve as preventive, and alternative therapies with potential uses in animal health. Derived from Greek, the word probiotic means "pro-life" and in the search to cover the correct mechanism of probiotics, this term has undergone several changes over the years. In animal production, it can be summed up as a "feed supplement for live microorganisms that beneficially affects animal flora by improving the microbial balance in the intestine" and should be viable and stable in the different breeding conditions [19].

**146**

The most used microorganisms as feed supplements are mainly bacteria, mostly from the group of Gram-positive *Bifidobacterium* and lactic acid bacteria (LAB). The genus *Enterococcus, Lactobacillus, Pediococcus, Streptococcus, Lactococcus*, and *Leuconostocos,* and also *Bacillus* are the most used. In addition to bacteria, fungi and yeast strains, mainly from the species of *Saccharomyces cerevisiae* and *kluyveromyces* are also used as probiotics [8, 19, 20]. A microorganism to be considered as a probiotic must meet some requirements: (1) to resist and quickly occupy the intestinal tract; (2) be part of the intestinal habitat; (3) survive the action of digestive enzymes; show antagonistic action against pathogenic microorganisms;(4) be non-toxic and non-pathogenic; (5) be stable and viable in commercial preparation and stimulate the immune system [21].

Several probiotic strains are included in poultry diets to promote animal growth and health, especially when conditions are challenging for health. Several studies have reported the beneficial effects of probiotics on various aspects of bird health. Furthermore, parameters related to supplementation with probiotics in diets increased body weight gain, feed intake and improved feed conversion rate in birds, were also reported (**Table 1**).

Until now, many mechanisms about the action were proposed. However, the main mechanisms of action of the probiotics are competition for binding sites, where the probiotics adhere to the intestinal epithelium wall, hindering competition and the joining of pathogenic microorganisms, this higher concentration of the beneficial microbiota also causes it to have advantage in competition for nutrients [12]. Supplementation with *Bacillus subtilis* improves the performance and immunity of broilers reared in warm conditions, and birds fed probiotic in the diet were able to deal more effectively with heat stress through immunity modulated by the


#### **Table 1.**

*Most evaluated parameters in broiler probiotics uses.*

microbiota [33]. Other studies, showed that nutritional effects where probiotics act by increasing fiber digestion in birds and enzymatic activity [34]. A competitive inhibiting effect, in which high amounts of Lactobacillus bacteria's produce organic acids that enable low pH in the crop that suppresses the colonization of pathogens in the digestive tract were also observed [21].

Testing different strains *(B. subtilis* DSM 32324*, B. subtilis* DSM 32325, and *B. amyloliquefaciens* DSM 25840*)* in isolation and in combination were showed that the tested strains had different abilities to degrade proteins and carbohydrates and inhibit the growth of *C. perfringens* in vitro. The in vivo results demonstrated that combined strains can act more efficiently than isolated strains on performance parameters as well as reducing mortality in birds challenged by *C. perfringens* [21].

Another study [35] used combined strains of *Bacillus licheniformis* and *Bacillus subtilis*, in order to investigate their effects and found that probiotic supplementation can increase profits if associated with dietary restriction. In addition to the feed efficiency, there was no influence on the carcass yield, the relative weights of the liver, gizzards, proventriculus, small intestine and bursa of fabricius, and the visible fat of the carcass was reduced. The association of probiotics with prebiotics was strongly recommended by these authors.

There is a belief that multiple strains combined with prebiotics have a better effect than isolated strains. FAO reported [20] on the use of probiotics in animals states that the benefit of using more than one strain in the same product still not clearly established.
