Phytobiotics as an alternative to antibiotic growth promoter for food animals

Sanjeev Kumar, TK Dutta, P Roychoudhury, Fatema Akter, PK Subudhi *

With the ever increasing human population the demand of animal protein (meat, milk, egg etc.) is increasing globally. To meet the increasing demand the animal husbandry sector of the world is under tremendous pressure to increase the production and productivity. In most part of the world the food animals are fed with growth promoting supplements like antibiotic growth promoters (AGP) to enhance the production by limiting the growth of pathogenic microorganisms (Arowolo and He, 2018).

A variety of synthetic feed additives including antibiotics and other growth promoting drugs are used in animal feeds to maximize the efficiency of production, product quality and to control diseases (Vidanarachchi et al., 2005). AGPs have been used widely in livestock production for almost 50 years. Although the modes of action of AGPs are not fully understood, the main effects are thought to be mediated via the gut-associated bacteria (Gaskins et al., 2002).

But with time AGP use in the animal feed has been decreasing due to its serious effects on public health and environmental issues (Arowolo and He, 2018). Sweden was the first country in Europe that banned the use of AGPs in 1986 followed by the European Union in 2006 because of the emergence of antibiotic resistant bacteria.

However, the ban on AGPs resulted in an increased incidence of enteric disorders in food animals. Before the implementation of this complete ban on the use of AGPs, some experts attempted to assess possible effects on growth rate and feed conversion efficiency and discussed possible alternatives after the ban (Wenk, 2003). This leads to increased demand to search for natural growth supplements as alternatives to AGPs.

The use of plants and plant bioactive compounds dates back thousands of years to the ancient Egyptians, Chinese, Indians and Greeks (Kamel, 2000). Chinese herbal medicines have been used for many centuries for treating various human and animal diseases (Li, 2000). In recent years, there has been an increased awareness of the potential that natural plant compounds have in the prevention and treatment. Phytobiotics are plant derived natural bioactive compounds that can be incorporated into diets to enhance the performance and well being of animals.

The content of active substances and the chemical composition of phytobiotics in the final products may vary widely depending on the plant parts used (seeds, leaves, etc.), geographical origins, and harvesting season (Windisch et al., 2008). Phytobiotics include a wide range of plant derived products such as essential oils, herbs and oleoresins. They can be added to the diet of commercial animals to improve their productivity through enhancing feed properties, promoting animals’ production performance, and improving the quality of products derived from those animals (Windisch et al., 2008).

Oligosaccharides and polysaccharides such as inulin (fructan), fructooligosaccharide (FOS) and arabinogalactans extracted from plants, and sulfated fucans extracted from seaweeds are potential substitutes for currently used AGPs (Iji and Tivey, 1998). Phytobiotics help in improvement of performance of food animals through various maechnisms and also can be a potential resource as an alternative to AGPs. The various mechanisms of action phytobiotics and their potential applications are described below.

1. Prebiotic effects

It has been observed that some plant extracts can influence the growth of commensal gastro-intestinal microflora by promoting the growth of good intestinal flora or by inhibiting the growth of opportunistic pathogens (Lan et al.,2005).

The protection of the gut environment is now known to play an important role in reducing disease in animals. Thyme and yarrow extracts are reported to have potential to reduce caecal counts of Clostridium perfringens,when incorporated in the broiler diets (Cross et al., 2004). The dietary supplementation of plant extracts containing capsaicin (1.98 g/100g), carvacol (4.95 g/100g) and cinnamic aldehyde (2.97 g/100g) reduced C. perfringens and Escherichia coli counts in colonic contents, wchih is comparable to birds treated with the antibiotic, avilamycin (Jamroz et al., 2003).

2. Antimicrobial effect

Antimicrobial action of phytobiotics is due to the presence of essential oils and phenolic compounds (thymol, carvacrol, phenylpropane, greaniol, etc.) (Yang et al., 2015).The antimicrobial activity (either bactericidal or bacteriostatic) of phytobiotic compounds has been investigated by several researchers against food borne organisms such as protozoa and fungi (Chao et al., 2000).

The presence of the hydroxyl group and delocalized electrons are important elements for their anti microbial action (Lambert et al., 2001). They suggested that the ability of hydrophobic essential oils to intrude into the cell membrane of pathogens, consequently disintegrating their membrane structures and causing ion leakage as a possible explanation of the antimicrobial activity of PFA. Some of them have shown promising activities against Eimeria species after experimental challenge in poultry (Giannenas et al., 2003). Phytobiotics also help in improving the microbial hygiene of carcasses (Aksit et al.,2006).

3. Prevent binding of harmful bacteria

Phytobiotics promote the binding of commensal microflora to the mucosa of the gastro intestinal tract either by specific adhesion of pathogens through the ‘lectin–receptor’ mechanism (agglutination) or by blocking the adhesion of pathogens onto the mucosal layer of the intestine. The phosphorylated mannan oligosaccharides (MOS) from yeast cell walls are extensively studied for their property to prevent the binding of harmful bacteria to GIT mucosa (Spring et al.,2000).

4. Immuno stimulatory effects

Certain plant polysaccharides act as immuno stimulatory (adjuvant effect) substances (Chen et al.,2003). Immune enhancer polysaccharides were obtained by Guo et al. (2003) from two mushroom species; Lentinus endodes and Tremella fuciformis, and a herb, Astragalus membranaceus radix, used in chickens to activate both innate and adaptive immunity. The dietary supplementation of fructooligosaccharides residues in phytobiotics leads to upregulation of immunoglobulin A (IgA) secretion in murine Peyer’s patch cells in the intestinal mucosa (Hosono et al., 2003).

5. Antioxidant and anti inflammatory action

Antioxidant properties of phytobiotics are due to their ability to scavenge free radicals that may play an important role in preventing some diseases (Kamatou and Viljoen, 2010).

Phytobiotic prevents oxidative damage by donating hydrogen or an electron to free radicals and delocalization of the unpaired electron within the aromatic structure (Fernandez-Panchon et al., 2008). Some essential oils have anti inflammatory activities, for example, chamomile essential oil has been used traditionally for centuries as a drug in eczema, dermatitis and other pronounced irritations (Kamatou and Viljoen, 2010).

Other essential oils (eucalyptus, rosemary, lavender, millefolia) from few plants (pine, clove and myrrh) have been used in mixed formulations as anti inflammatory agents (Darsham and Doreswamug, 2004). Rosmarinic acid, oleanolic acid and ursolic acid are the major nonvolatile secondary metabolites found in Origanum spp. with strong antiinflammatory properties (Shen et al., 2010).

6. Growth stimulation

Mohammadi et al. (2015) reported that addition of herbal products to diets has growth promoting effect on poultry and swine. The pigs fed with the diets supplemented with phytobiotics have shown that weight gain and digestibility of dry matter and crude protein were improved by 10.3, 2.9 and 5.9%, respectively (Li et al., 2012) due to improved nutrients digestibility, better average daily gain (ADG) and improved feed conversion ratio (FCR) (Yan et al, 2010).

Conclusion

Use of antibiotics in animal diets to meet the increasing demand of animal protein has been a common practise in livestock farming. A recent study estimating global antibiotic use in poultry, swine and cattle in 2010 indicates that India accounts for 3% of global consumption and is among the top consumers worldwide besides China, USA, Brazil and Germany. It is estimated that the use of antibiotics in animal husbandry will increase by 82% in India by 2030.

This rise in use of antibiotics in livestock farming will be a hurdle in the efforts used to tackle the menace of AMR in the society. However, the use of phytobiotics provides an alternative that can help to tackle the problem of developing AMR associated with livestock and animal based food products.

The available literatures provided an indication and justification that phytobiotics may have the potential to increase the production performance and productivity of the food animals in a similar way as AGPs in near future. More research efforts should be on table to develop and marketing the non-antibiotic animal growth promoter to maintain the sustainability of animal husbandry and to meet the ever increasing demand of animal proteins.


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