**1. Introduction**

Phytogenics, also referred to as plant secondary metabolites, phytochemicals, phytobiotics, or botanicals, are plant-derived products/extracts (PE) and include a wide range of substances. These include those derived from herbs and spices such as essential oils and oleoresins, reported

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

to exhibit growth promoting and/or therapeutic properties [1, 2]. Initially, PE were extensively studied because of the adverse effects they have when ingested by animals [3]. However, the use of PE as an alternative to in-feed antibiotics to prevent the risk of developing pathogens resistant to antibiotics and to satisfy consumer demand for a poultry food chain free of drug residues has gained recent interest [4]. Antibiotics have been added to poultry diets to maintain health and production efficiency in the last few decades [5]. The withdrawal of in-feed antibiotics as growth promoters have increased the risk of bacterial disease, especially in growing poultry [6]. The ability of PE to contribute to the health of the host is well documented [1]; however, the exact mechanisms by which PE exerts its effects remain speculative. As documented, PE are composed of a diverse group of natural products [7]. However, while some are nutritionally valuable, others have no nutritional value or even possess antinutritional properties. This is likely due to PE varying widely in their chemical structures [3]. Since the effects of PE depend to a great extent on the chemistry of the compounds, it is impossible to have a uniform explanation of their mode of action. This chapter provides a brief overview of the main benefits of adding selective PE to poultry diets. Specifically, it describes the mode of action of carvacrol, cinnamaldehyde and capsaicin when fed to broiler chickens as a standardised commercial mix.

eggs (reviewed by [1]). Furthermore, research with rats [13] and poultry [14] suggested that dietary phytogenic supplements may improve the antioxidative status of the animals, reducing intestinal cell damage and sustaining the integrity of the intestinal mucosal layer. These supplements acted as effective free radical scavengers and also influenced the *in vivo* antioxidant defence systems in the animal. In addition, diets supplemented with turmeric, curcumin, green tea, grape seed proanthocyanidins and society garlic, which all possess antioxidative properties, reduced small intestinal lesion scores, lowered oxidative stress and improved weight gains during coccidial infection (summarised by [6]). All these compounds may exert their anticoccidial activity by protecting infected tissues from oxidative damage and therefore

Plant Extracts, Energy, and Immune Modulation in Broilers

http://dx.doi.org/10.5772/intechopen.77220

105

Immunomodulation is described as a change of the indicators of cellular and humoral immunity and nonspecific defence factors [15]. Immunomodulation can present as immunosuppression (substances that inhibit the immune system) or immunostimulation (substances that activate or induce the mediators or components of the immune system), thus regulating or

It has been speculated that the benefit of using PE in animal diets is associated with reduced intestinal inflammation in part from a reduction of proinflammatory cytokines. One study [18] reported that cinnamaldehyde suppressed the lipopolysaccharide-induced production of tumour necrosis factor (TNF), interleukin 6 (IL-6) and IL-1, thus suggesting that the inclusion of cinnamaldehyde could show suppressive effects on the production of various types of inflammatory cytokines. Similarly, [19] also found that a mixture of capsicum and turmeric oleoresins was an effective phytonutrient against clinical signs of experimental avian necrotic enteritis when supplied in dietary form. Research by Lee et al. [20] suggested that immunomodulatory effects are responsible for improved weight gain, oocyst shedding, increased interferon gamma (IFN-γ) and IL-15, when powder from oriental plum (a plant rich in phenolic compounds) was fed to coccidia challenged birds. Furthermore, supplementation with Chinese mushroom and herb extracts resulted in enhancement of both cellular and humoral

There is strong evidence that PE have antimicrobial properties, being able to reduce the proliferation of pathogenic organisms at minimal inhibitory concentrations of 0.05–5 microliters per millilitre *in vitro*, and at higher concentrations (0.5–20 microliters per gram) in food [22]. While these levels are unlikely to be met in animal feedstuffs, and therefore not the primary use of PE in feed, there is evidence that PE have effective antimicrobial action against pathogens common in poultry production. These include *Escherichia coli* and *Clostridium perfringens* [23–25]. Pathogenic microorganisms in the gut are able to trigger immune responses in the gastrointestinal tract. This results in inflammation of the intestine contributing to poor gut health. In addition to reducing pathogenic challenge, PE may also possess direct immunomodulation properties. For example, it is known that cinnamaldehyde in particular is involved in gene regulation, including antigen presentation, humoral immune response and

altering the scope, type, duration or competency of the immune response [16, 17].

immune responses in *Eimeria tenella* infected chickens [21].

reducing the severity of coccidiosis.

**2.3. Immune status**

inflammatory disease [26].
