What are probiotics?
(Biological promoters)
The term probiotic was proposed for the first time in 1965. Currently the term Probiotic is used to designate a food supplement composed of pure or compound cultures of live microorganisms, with the ability to install and proliferate in the intestinal tract and showing the action of growth promoters, benefiting the host’s health by stimulating the existing properties of the natural microflora.
Currently, the incentive for the use of Probiotics in the control of poultry infection by salmonellas was provided by experiments carried out by Finnish researchers (Nurmi & Rantala, Nature, 1973). In their experiments, the authors observed that when the intestinal contents of normal adult birds were orally administered to one-day-old chicks, this altered their sensitivity to infection by Salmonella spp., avoiding their establishment in the intestine. This idea was classified as “Competitive Exclusion” and became known as “the Nurmi concept”. Probiotics can also prevent intestinal colonisation by other pathogens, such as Escherichia coli and Campylobacter spp.. At about the same time, other authors demonstrated that the application of a probiotic constituted of L. acidophilus, improved feed conversion ratio and weight gain in treated birds (Tortuero, Poult. Sci., 1973).
Modern poultry exploration, aimed at producing both meat and eggs, practically “sterilises” the incubating egg. There is also a productive concept that the one-day-old chick should contain the lowest possible contamination index of any nature. Modern poultry rearing techniques demand an initial rearing environment with a bacteriological quality of the water and feed that makes difficult and retards the establishment of an intestinal microflora, which could not be different due to the potential risks. Part of these risks has been minimised by the use of so-called “growth promoters”. However, under normal conditions, nature has taught us that immediately after birth, the chicks are in contact with their mother’s faeces as their first source of “food”. This does not occur by chance. The faeces of the chicks’ mothers contain elements extremely important for immuno-protection, and for the stimulation of the development and functioning of the intestinal tract of the young birds. Probiotics and Prebiotics represent a technological advance, transferring the beneficial effects provided by nature and applying them to industrial rearing.
The intestinal microflora of birds
The intestinal microflora of birds is composed of innumerable bacterial species, forming a complex, dynamic system. Those that initially colonise the intestinal tract tend to persist throughout the bird’s life, making up the intestinal microflora. The formation of this microflora occurs immediately after birth and increases during the first weeks of life, until it becomes a predominantly anaerobic bacterial population.
The main genera identified in the caecal microflora of birds are: Bacillus, Bacteroides, Bifidobacterium, Citrobacter, Clostridium, Enterobacter, Enterococcus, Escherichia, Eubacterium, Fusobacterium, Lactobacillus, Lactococcus, Pediococcus, Peptostreptococcus, Propionibacterium, Ruminococcus, Serratia, Veillonella and Streptococcus.
The persistence and maintenance of these bacteria in the intestinal tract occurs mainly in two ways: (i) fixed or intimately associated with the intestinal epithelium, multiplying more rapidly then their elimination by intestinal peristalsis. This is typically the case with some species of Lactobacillus and Enterococcus. Others (ii) remain free in the intestinal lumen, due to their inability to adhere to the intestinal epithelium. In this case, their permanence is due to aggregation with other bacteria, which, for their part, adhere to the enteric mucous lining.
Any factor leading to a loss of the intestinal microflora equilibrium, such as the use of anti-microbial agents or stress of any nature, can allow for the installation and multiplication of pathogenic microorganisms. Thus it is evident that intestinal microflora equilibrium reflects directly on the good state of the host’s health.
Table 1 - The action of beneficial and prejudicial bacteria in the human digestive tract
Beneficial bacteria |
Prejudicial bacteria |
|
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Probiotics can contain totally known and quantified bacteria or non-defined bacterial cultures. Enterococcus, Bacteroides, Eubacterium and especially Lactobacillus and Bifidobacterium are present in all the defined culture mixtures. When bacteria with Probiotic capacity are removed (isolated) from their conventional habitat and sub-cultured and/or freeze dried, they lose some of their properties. On the other hand, neither the total composition nor the perfect composition between them that best stimulate the Probiotic properties “in vivo”, are known. For these reasons, products with non-defined cultures show better Probiotic action than defined cultures.
Apparently, a greater number of bacterial species determines a more effective Probiotic. Some form of protection is evident as from four bacterial species and protection tends to be more effective in mixtures containing more than 20 species. Cultures containing about 50 bacterial species show greater chances of maintaining the intestinal microflora equilibrium. The bacteria should be host-specific so as to attain maximum product efficiency, that is, bacteria showing Probiotic activity in swine may not show such activity in birds.
The beneficial action of the Probiotics used in aviculture occurs in two main ways: (i) determining better zootechnical indexes, greater productivity, increases in weight gain and better feed conversion ratio; (ii) reducing the colonisation by some pathogens, such as, for example Salmonella.
Desirable properties of a Probiotic
- Can be stored without loss of viability until the moment of use;
- Show conditions to remain in the intestinal ecosystem;
- The host animal should obtain benefit from its use.
How do Probiotics act:
Various beneficial actions are attributed to the use of Probiotics, and some are shown in Table 2. However their mechanism of action has yet to be entirely elucidated. The following are amongst the main modes of action of Probiotics:
(a) Competition for binding sites;
(b) Production of anti-bacterial substances;
(c) Competition for nutrients;
(d) Stimulation of the immune system.
It is also known that there is synergism between these actions.
a. Competition for binding sites. This concept has become better known as “Competitive Exclusion”. The Probiotic bacteria occupy the binding sites (receptors or binding points) on the intestinal mucous, forming a physical barrier to the pathogenic bacteria. Thus the pathogenic bacteria are excluded by competition.
b. Production of anti-bacterial substances. Probiotic bacteria produce compounds such as bacteriocins, organic acids – short chain volatile fatty acids (propionic, acetic, butyric, lactic) and hydrogen peroxide, which show anti-bacterial actions especially with respect to pathogenic bacteria. The Probiotic bacteria feed on ingredients totally or partially not degraded by the normal digestive enzymes, or that were intentionally added to the diet. These substances, intentionally added with the finality of “feeding” the Probiotic bacteria, are known as Prebiotics, and will be discussed in more detail in a later section.
Table 2 - Beneficial actions attributed to the use of Probiotics- Aid the digestion and absorption of nutrients (involvement in the intestinal biochemistry, especially with respect to their action on bile salts);
- Inhibitory action on the growth of pathogenic bacteria (production of bacteriocins that act by inhibiting the growth of other bacteria);
- Production of lactate and acetate that reduce the pH of the medium, exerting an anti-bacterial effect;
- Production of metabolites that inhibit pathogenicbacteria, both gram negative and gram positive;
- Production of the B group vitamins;
- Stimulate the immune system by activating microphages;
- Activate the immune system against malignant cells;
- Restore the intestinal microflora after therapy with antiobiotics.
c. Competition for nutrients. The lack of available nutrients in the intestinal lumen that can be metabolised by pathogenic bacteria is a limiting factor in the maintenance of these bacteria in the environment.
d. Stimulation of the immune system. The immunological defence of the host is directly related to the intestinal microflora, and an animal or man is simply incapable of survival if he fails to develop a normal intestinal microflora. Some of the Probiotic bacteria are directly related to the stimulus of an immune response by increasing the production of antibodies, activation of microphages, proliferation of T cells and production of interferon, amongst other actions.
How Probiotics are applied
The way of administering Probiotics can also determine a better or worse capacity for intestinal colonisation by the bacteria present in the product used. Independent of the via, the probiotics should be administered to the birds as early as possible, so that the bacteria present in the product colonise and multiply in the host’s intestinal tract, initiating their beneficial activities before the host is contaminated by some pathogen.
The Probiotics can be administered to bird in several ways:
- By addition to the feed;
- By addition to the drinking water;
- By spraying the bird;
- By cloacal inoculation;
- By inoculation of embryonated eggs;
- Via the litter used;
- In gelatine capsules;
- Experimentally, via intra-oesophagus.