Phytobiotics as an alternative to antibiotic growth promoter for food animals

Sanjeev Kumar, TK Dutta, P Roychoudhury, Fatema Akter and 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).

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