By-Dr Deepak Prasad Sinha,Poultry consultant,Patna
Poultry probiotics or direct fed microbials (DFM) are live microorganisms that can be incorporated in diets in order to:
• Populate the intestine with beneficial bacteria
• Modulate the conditions within the gastrointestinal tract
The effects of poultry probiotics are particularly important in young animals in which stable intestinal bacteria have not yet been established.
By adding probiotics to feed or water, the intestine is populated with beneficial bacteria avoiding or decreasing the extent of pathogen colonization (Nurmi and Rantala, 1973).
The efficacy of different probiotics has been demonstrated in modern poultry systems. Because antibiotics are being removed from the routine practices of animal husbandry, probiotics are now considered a promising tool to prevent pathogens from causing health and disease challenges.
Probiotic, prebiotic and symbiotic———-
Probiotics can be combined with prebiotics in order to nourish the beneficial bacteria and achieve better results. The probiotic plus prebiotic combination is known as a synbiotic.
A prebiotic is a non-digestible additive often consisting of natural dietary fibers such as fructooligsaccharides (FOS) that stimulate the growth and activity of beneficial bacteria in the colon, thus improving host health (Gibson and Roberfroid, 1995).
A synbiotic is a combination of probiotic and prebiotic products (Patterson and Burkholder, 2003), often with the aim of improving efficacy. PoultryStar® is an EU-authorized synbiotic (probiotic plus prebiotic).
Table 1. Common definitions of probiotics (direct-fed microbials) –related terms
Term Definition
Probiotic Beneficial bacteria supplemented to a diet
Prebiotic Substances delivered to nourish beneficial bacteria
Synbiotic A combination of probiotics and prebiotics
The poultry industry has become an important economic activity in many countries. In large-scale rearing facilities, where poultry are exposed to stressful conditions, problems related to diseases and deterioration of environmental conditions often occur and result in serious economic losses. Prevention and control of diseases have led during recent decades to a substantial increase in the use of veterinary medicines. However, the utility of antimicrobial agents as a preventive measure has been questioned, given extensive documentation of the evolution of antimicrobial resistance among pathogenic bacteria. So, the possibility of antibiotics ceasing to be used as growth stimulants for poultry and the concern about the side-effects of their use as therapeutic agents has produced a climate in which both consumer and manufacturer are looking for alternatives. Probiotics are being considered to fill this gap and already some farmers are using them in preference to antibiotics .
Adding the so-called beneficial bacteria to the digestive tract of poultry is not a new concept, however, a complete understanding of where, when and how to use them still has escaped us in its entirety. A strikingly crucial event in the development of probiotics was the finding that newly hatched chickens could be protected against colonization by Salmonella enteritidis by dosing a suspension of gut contents derived from healthy adult chickens . This concept is called competitive exclusion.
The impact of biotechnology in poultry nutrition is of significant importance. Biotechnology plays a vital role in the poultry feed industry. Nutritionists are continually putting their efforts into producing better and more economical feed. Good feed alone will not serve the purpose but its better utilization is also essential. Dietary changes as well as lack of a healthy diet can influence the balance of the microflora in the gut thus predisposing to digestion upsets. A well-balanced ration sufficient in energy and nutrients is also of great importance in maintaining a healthy gut. A great deal of attention has recently been received from nutritionists and veterinary experts for proper utilization of nutrients and the use of probiotics for growth promotion of poultry.
In broiler nutrition, probiotic species belonging to Lactobacillus, Streptococcus, Bacillus, Bifidobacterium, Enterococcus, Aspergillus, Candida, and Saccharomyceshave a beneficial effect on broiler performance , modulation of intestinal microflora and pathogen inhibition , intestinal histological changes , immunomodulation , certain haemato-biochemical parameters , improving sensory characteristics of dressed broiler meat and promoting microbiological meat quality of broilers .
Mechanisms of Action —————–
How probiotics work against pathogens—-
Several proposed mechanisms explain the mode of action of probiotics against pathogens, namely:
1. Competitive exclusion
2. Bacteriocin production
3. Immune stimulation
4. Improvement on gut health and integrity
Probiotics competitively exclude pathogens—–
Competitive exclusion refers to the blockage of cellular receptors on the luminal surface of epithelial cells, mechanically avoiding the entrance of pathogens. This can be supported by in vitro assays that show the capacity of selected probiotic bacteria to adhere to intestinal cells (Pascual et al., 1999; Ibnou-Zekri et al., 2002).
Remarkably, the ability to attach to the surface of intestinal cells varies among different strains of the same species of bacteria (Ibnou-Zekri et al., 2002). Competitive exclusion also considers the consumption of available nutrients by beneficial bacteria limiting resources and space for pathogenic bacteria.
Probiotics produce bacteriocins that target pathogens——
Another mechanism that reduces bacterial viability is the production of harmful substances that specifically target pathogens, like H2O2 and bacteriocins (Oh et al., 2000; Gillor et al., 2008).
Bacteriocins are amino acidic molecules that have bactericidal properties on genetically related organisms. Several bacteriocins have been identified. Small bacteriocins tend to be heat-stable whereas large bacteriocins tend to be heat-labile.
While described bacteriocins are mostly effective against Gram-positive bacteria, there are some bacteriocins already described which are effective against Gram-negative organisms (Ralph et al., 1995; Servin, 2004).
Because of their amino acidic origin, bacteriocins are susceptible to proteolytic enzymes. There is another group of non-acid substances that are resistant to heat and proteolytic enzymes and thus belong to a different category of inhibitory compounds produced by commensal bacteria. Most of these are not fully identified compounds but with established inhibitory activity against Clostridium‚ Bacteroides‚ Enterobacteriaceae‚ Pseudomonas‚ Staphylococcus‚ and Streptococcus (Silva et al., 1987).
The right probiotics support the immune system——–
Stimulation of the immune system, or immunomodulation, is another theory that explains the efficacy of probiotics. The intestinal tract of newborns is basically sterile. Bacteria that first colonize the gut influence the gene expression of epithelial cells influencing in turn the subsequent bacterial colonization of the intestine.
As an immune organ, the intestine has a large component of lymphoid tissue (GALT, or gut-associated lymphoid tissue) which also needs proper stimulation from commensal microorganisms for maturation.
Chickens that have been immune stimulated with probiotics in the diet have shown increased secretion of anti-clostridial IgA antibodies (Hamid et al., 2006). On the other hand, the intestine must also peacefully coexist with commensal bacteria and antigens of alimentary origin (oral tolerance). In addition, non pathogenic bacteria are able to send stimulatory signals to the enterocytes which limit the production of pro-inflammatory cytokines while promoting the production of anti-inflammatory cytokines (Neish et al., 2000). This observation can be supported by germ-free mice that show continuous inflammation and inadequate immune responses against normal dietary antigens (Servin, 2004).
It should be noted that the immune-stimulatory function of commensal bacteria is strain specific and even closely related bacteria stimulate the immune system in different ways (Ibnou-Zekri et al., 2002). Theoretically, probiotics could achieve benefits by either pro- or anti-inflammatory effects. For example, in human medicine it could be desired to reduce inflammation in patients undergoing chronic inflammation (Crohn’s disease). On the other hand, enhanced inflammation and direction of the immune system towards the cellular component of the immune response may help fighting coccidia in poultry.
Probiotics support epithelial cells————-
In addition to the anti-pathogenic activity that probiotics have, it has been demonstrated that indigenous bacteria of the intestine also contribute to the healthy development of epithelial cells. Actually, indigenous bacteria can stimulate enterocytes to produce and release active gastrointestinal peptides that impact the regulation of epithelial structure and intestinal endocrine cells (Servin, 2004). It is also becoming clear that commensal bacteria modulate gene expression of epithelial cells influencing nutrient absorption, intestinal maturation and improvement of the mucosal barrier (Servin, 2004).
Some strains of Lactobacillus are able to reduce the epithelial invasion of enterohemorrhagic E. coli (EHEC) without decreasing the viability of the pathogen. Since this effect is only observed with live Lactobacillus, it is thought that it is the result of the interaction of commensal bacteria and intestinal epithelium that induces protective changes on the enterocytes interfering with the internalization process of EHEC (Hirano et al., 2003). There is increasing evidence indicating that probiotics exert selective activation of certain epithelial genes. Similarly, the modulation of immune response obtained with probiotics seems to be strain-dependent (Didierlaurent et al., 2002).
Criteria for Selection of Probiotics in the Poultry Industry ———–
The perceived desirable traits for selection of functional probiotics are many. The probiotic bacteria must fulfill the following conditions:
it must be a normal inhabitant of the gut, and it must be able to adhere to the intestinal epithelium to overcome potential hurdles, such as the low pH of the stomach, the presence of bile acids in the intestines, and the competition against other micro-organisms in the gastro-intestinal tract . The tentative ways for selection of probiotics as biocontrol agents in the poultry industry are illustrated in Figure 2. Many in vitro assays have been developed for the pre-selection of probiotic strains . The competitiveness of the most promising strains selected by in vitro assays was evaluated in vivo for monitoring of their persistence in chickens . In addition, potential probiotics must exert its beneficial effects (e.g.,enhanced nutrition and increased immune response) in the host. Finally, the probiotic must be viable under normal storage conditions and technologically suitable for industrial processes (e.g., lyophilized).
New scientific insights about probiotics ————-
The scientific community is changing its way of looking at the mode of actions of probiotics. Since probiotics have been commercially available, they have been expected to exert their benefits derived from their ability to multiply, produce certain metabolites and colonize the surface of the intestinal epithelium.
Today (and for the last 10 years), researchers are challenging the “classic” mode of actions of probiotics with novel ones. So far, there is a good bulk of evidence suggesting that some of the effects of probiotics like the anti-inflammatory effect are mediated by fingerprints (structural molecules) rather than by the whole organisms or their ability to colonize the intestine.
In-case probiotics are also partly inactivated in the course of feed processing or antibiotic treatment at therapeutic doses; there are beneficial mechanism that do not depend on live bacteria and which will remain unaltered. As long as the effector molecules within the probiotics remain with the appropriate structure a biological effect should be expected.
Commonly used probiotic bacteria in animal feeding are lactic acid-producing strains like Enterococcus, Pediococcus, Lactobacillus and Bifidobacterium, which are also genera commonly found in the poultry gut. Several scientific studies have shown that they have a beneficial effect on performance, pathogen inhibition, modulation of intestinal microflora and immuno-modulation, especially during critical times in the production cycle when a protective gut microflora is not yet established or a disrupted probiotic application exerts its benefits.
Probiotics to protect newly hatched chicks—————–
Under normal conditions (i.e. in the wild), animals pick up their microflora from adult animals and from the environment very quickly, but under conditions of modern animal production, things are different. Commercial broiler chicks hatch in extremely clean conditions and don’t have contact with adult animals. Then they are transferred in houses previously cleaned and disinfected. For them, to build up and establish a well-balanced microflora is difficult. During that time, the chicks are not protected against the colonization with pathogenic microbes.
For the chicks, it is crucial to develop a protecting microflora as early and fast as possible, which can be supported by the application of probiotics. Probiotic products can be sprayed onto the chicks already in the hatchery or be applied via the drinking water during the first days of life. They provide conditions in the chicks’ intestines that favour the colonization by beneficial microbes.
Probiotics and antibiotic therapy ————-
Antibiotics are useful tools to eliminate undesired pathogens. However, they also eliminate a large proportion of the beneficial microflora which needs to be re-established after the antibiotic treatments ends to avoid fast growth of opportunistic pathogens. Antibiotics may eliminate the pathogens, but they often do not sufficiently control inflammation. In many cases of pathogenic invasion, an exaggerated response of the immune system may cause even more damage than the pathogen itself.
Probiotics can help modulate the immune system. It is very common in the field to see the severe inflammation of the intestinal mucosa regardless of the ongoing antibiotic therapy. Intestinal inflammation is related to increased velocity of the intestinal content. As a consequence, feces with increased amount of humidity, gas, excess of indigested feed particles or fragments of intestinal mucosa may be a common finding derived from intestinal inflammation. Confirmation of intestinal inflammation can be obtained from necropsied animals.
The use of probiotics is recommended to fight side effects of diseases that will not be improved by the use of antibiotics. In this scenario, antibiotics in therapeutic doses should be taking care of pathogens; however, the intestinal inflammation often remains unattended. Even inactivated probiotics exert a beneficial effect reducing inflammation by means of their cellular structure and particularly their intact DNA molecules and receptors, which are unique to every probiotic strain.
Probiotics and Necrotic enteritis —————–
Necrotic enteritis is one of the world’s most common and financially crippling poultry diseases, which when triggered can cause mortality rates of up to 50%. A team of USDA research scientist has investigated if the use of a multi-species probiotic may be beneficial in the control of poultry diseases, which are related to Clostridium perfringens. In conclusion, the data of these studies suggest that the probiotic was able to control poultry diseases like Necrotic enteritis and Gangrenous dermatitis.
The use of probiotic products can provide the poultry industry with an alternative management tool that has the potential to promote better intestinal health by managing the composition of the microbial population in the GI tract, to protect poultry flocks from infections with pathogenic bacteria and to decrease monetary losses due to pathogens.
Conclusions ———–
The concept of probiotics in recent year is no more confusing as was earlier thought. It now constitutes an important aspect of applied biotechnological research and therefore as opposed to antibiotics and chemotherapeutic agents can be employed for growth promotion in poultry. In past years, men considered all bacteria as harmful, forgetting about the use of the organisms in food preparation and preservation, thus making probiotic concept somewhat difficult to accept. Scientists now are triggering effort to establish the delicate symbiotic relationship of poultry with their bacteria, especially in the digestive tract, where they are very important to the well being of man and poultry. Since probiotics do not result in the development and spread of microbial resistance, they offer immense potential to become an alternative to antibiotics. The probiotics could be successfully used as nutritional tools in poultry feeds for promotion of growth, modulation of intestinal microflora and pathogen inhibition, immunomodulation and promoting meat quality of poultry.
Reference:On request.
