Probiotics and Medicinal Plants in Poultry Nutrition: A Review

The use of medicinal plants and probiotics has recently gained interest since the ban on the use of antibiotics as growth promoters by the European Union in 2006. They are new alternatives to bridge the gap between food safety and production. Medicinal plants are cheaper and loaded with several minerals, vitamins and phytochemicals such as: alkaloids, saponin, flavonoids, phenols, tannins etc. which allows them to perform multiple biological activities. Probiotics on the other hand, repopulates the gastro intestinal tracts (GIT) with beneficial bacteria which controls the action of pathogens and control their population, thereby reducing mortality and improving general performance of an animal. Keywords— Probiotics, medicinal plants, pathogens, phytochemicals.


I. INTRODUCTION
Poultry production has experienced a remarkable growth within the past four decades in its bid to attain viable level of production but there are still a lot of problems confronting the industry such as disease, high cost of feed cost and most recently the indiscriminate use of antibiotics. The sub-therapeutic use of antibiotics in poultry production is a public health concern because of antimicrobial resistance and the presence of their residues in final products leading to several health challenges in humans. These situations prompted the European Union in 2006 to place a ban on the use of the use antibiotic feed additives to promote food safety. Among the potential alternative to antibiotics is the use of medicinal plants (phytobiotics/phytogenics) and probiotics which contains one or more useful bacteria or yeast (Waldroupet al., 2003;Navaet al., 2005) which promotes healthy gut and prevents disbiosis which could occur during stress, prolong water deprivation, feed fasting and infections (caused by viruses, bacteria, fungi and protozoa), causing an imbalance of flora with a proliferation of undesirable microorganisms (Filipe (2014). According to Filipe (2014), probiotics administration repopulates the GIT with beneficial with beneficial bacteria which curbs the action of pathogens and controls their population. This is especially after stressful events such as drastic changes in the diet, fasting, erratic temperatures or after exposure to aggressors such as enteritis of bacteria or viral origin in the microbiota and mycotoxin contamination in feed.

MECHANISM OF ACTION OF PROBIOTICS
The mode of action of probiotics is not always well understood due to different strains that may have various functions and survivability throughout the gut affecting the host in different ways. The effects of probiotics can be classified in: 1) Interaction between probiotic-microbe-gut epithelium: Adhesion to mucosal epithelial cells, stimulation of mucus secretion, prevention of adhesion of pathogens as probiotics blocking intestinal receptors, thereby excluding pathogens, enterotoxins and hampering proliferation of pathogens, competition with pathogens for important nutrients, secretion of antimicrobial and antitioxin substances that affects establishment and or replication of pathogens in the gastrointestinal tract (Collado, 2009) 2) Interaction between probiotic-immune system: Immunemodulation by innate as well as systemic ways, enhancing and reinforcing gut integrity and gut barrier function, eventually decreasing secretory and inflammatory molecules against microbial infection (Servin, 2004). The general mechanisms by which probiotics may have an effect can be divided into various categories: adhesion activity to gut mucosal epithelium, antitoxic effect, modulation of immune system, production of antimicrobial substances and competitive exclusion between probiotics and pathogenic bacteria.

RELEVANCE OF A BALANCED GUT
According to Klasing (1987), there is a correlation between gut microbiota imbalance and poor growth performance. In other words, pathogenic organisms compete with animals for nutrients which could lead to poor performance and eventually death depending on its severity. Kristy (2015) opined that the acquisition of a positive microbiota in the first few days after hatching has a profound effect on the overall health of the bird. Similar observation was made by Filipe (2014) who reported that newly hatched industrial chicks do not come into contact with mother hens and are placed in a clean, sanitized environment with little opportunity for rapid development of a protective intestinal microflora that can successfully compete with pathogens. The first days of life are a critical period of time with high risk of infection by pathogens such as E.coli, Salmonella etc. that may be present in the litter. Thus, probiotic supplementation is beneficial measure as expressed in Fig 2.

PROBIOTICS FOR POULTRY
In modern broiler production many factors can enhance stressors, they include feed changes or imbalances, transportation, processing at the hatchery and high stocking densities. During post hatching period, which ultimately affects the colonization of the gastrointestinal tract by bacterial pathogens due to weakened immune system, posing a threat to bird and food safety.
In a comprehensive research in turkeys and chickens, commercial researches have established that proper administration of probiotics mixture increased performance, reduced costs of production as well as was effective in reducing abdominal fat deposition (Vincente et al, 2007). Timmerman et al. (2006) reported that the main factors affecting the efficacy of the probiotic preparations depend on way and timing of the administration. Application through the feed than application in the drinking water resulted in a higher increase of average daily gain.
Eggs production has been also investigated in relation to probiotic application. The use of Enterococci as probiotics in chickens prolonged feeding with E. faecium based probiotics increased egg laying intensity and feed conversion efficiency (Koudela et al, 1996). In poultry, benefits of yeast probiotic supplementation are established in broilers' production performance and increased resistance of chickens to enteric pathogens infections (Salmonella, Campylobacter jejuni, E. coli or C. perfringens) (Banjeree and Pradhan, 2006). Furthermore, supplementation with yeast treatment significantly decreased the frequency of Salmonella colonization to lower than the pre-stress (before transport) levels, whereas non-supplemented birds had higher levels of Salmonella colonization (Line et al., 1997).

MEDICINAL PLANTS
The use of plants in traditional medicine has been in existence for thousands of years because plants have proven to be a natural renewable resource with valuable bioactive compounds (Cherkupallyet al., 2017; Lina, 2017; Oluwafemi et al., 2020) and also provided a clue on the discovery of new products of medicinal value for drug development (Senthilkumaret al., 2018).
According to Rates (2001) out of the about 250,000 -500,000 plant species estimated by the WHO (1992), only a small percentage has been investigated phytochemically and even a smaller percentage has been properly studied in terms of their pharmacological properties.
The primary benefits of using plants or herbs (essential oil, spices, extracts) is that they are relatively safer than synthetic alternatives offering profound therapeutic benefits and more affordable (cheaper) in the treatment of diseases (Manjuet al., 2011).

Maintaining the integrity of the gastro intestinal tract (GIT)
According to Bravo and Ionescu (2008) mixture of a mixture of carvacrol, cinnamaldehyde and capsicum oleoresin in broilers stabilizes the intestinal microbiota and reduces microbial toxic metabolites in the gut, owing their direct antimicrobial properties on various pathogenic bacteria which result in relief from intestinal challenge and immune stress. Treatments were control diet (T1), control diet with 1% thyme seed powder (T2), control diet with 1% garlic powder (T3) and control diet with 0.5 % thyme seed and 0.5 % garlic powder (T4). E.coli count in the gut of the birds did not show dietary treatments compared to control.
However, Lactobacilli in the gut of broilers significantly (P<0.05) increased in T2, T3 and T4 compared to that of T1. It was concluded that thyme and garlic could provide positive advantages to the colonization and proliferation of Lactobacilli.
Alagbeet al. (2019) conducted to evaluate the carcass, caeca microbial parameters of broilers fed different levels of mixed lemon grass and garlic extract (CLGE). Five hundred broiler chickens (Ross 308) were allotted to five treatments with five replicate consisting of 20 birds each in a completely randomized design (CRD).
There were also significant differences (P<0.05) in the caeca microbial population of E.coli and lactobacillus count as well as the antibody titer against Newcastle and gumboro disease.
Birds in T5 had the lowest E.coli count (9.00 cfu/g) when compared to T1 (22.19 cfu/g) with the highest proportion of the bacteria. It was concluded that CLGE could be given to broilers at 12.0ml/liter without any negative effect on the health and can be used to effectively replace antibiotics.