A major feature of poultry production today is the reduction of in use of antibiotics and other allopathic medicinal products, largely due to concerns over bacterial resistance. Alongside this trend, however, is an ever-growing demand for low-priced, high quality food, improved feed hygiene, greater poultry health and welfare, and reduced environmental impact.

Much research has focused on the development of alternative strategies to maintain poultry health and enhance performance within intensive systems, and numerous substances, commonly known as natural growth promoters (NGPs) have been identified as effective alternatives to antibiotics. Phytobiotics are NGPs that have been growing in popularity as feed additives, due to their benefitical effect on gut health and immunity and growth performance.

Phytobiotics can be defined as plant derived products added to feed in order to improve performance. They originate from leaves, roots, tubers or fruits of herbs, spices and other plants. They may be available in solid, dried, and ground forms, or as extracts (essential oils). In simple terms, phytobiotics are products of plant origin, and preparations such as thyme, oregano, turmeric and garlic are gaining interest among researchers and poultry producers.

The beneficial effects of phytobiotics in poultry may arise from the activation of feed intake and the secretion of digestive enzymes, immune stimulation, antibacterial, coccidiostatic, anthelmintic, antiviral or anti-inflammatory activity, or from antioxidant properties. Many plant secondary metabolites, such as isoprene derivatives, flavonoids and glucosinolates, may act as antibiotics or as antioxidants in vivo. As a result of these beneficial effects, they lead to an increase in performance.

Phytobiotics produce their beneficial effects in several ways:

1. Stimulation of feed intake and digestive secretions

Herbs develop their initial activity in the feed as flavour and, therefore, influence eating patterns, the secretion of digestive fluids and total feed intake. Stimulation of digestive secretions, including saliva, digestive enzymes, bile and mucus is often considered to be one of the important actions of phytobiotics.

A product from the rhizomes of Sanguinaria canadensis is frequently used in Europe for poultry while garlic and horseradish, when included in feed, stimulate the production of saliva and gastric juices. Turmeric, a powder derived from the rhizome of Circuma longa has been shown to improve feed intake in poultry when used at 0.25% in feed.

A study conducted at the Directorate of Poultry, Rajendranagar, Hyderabad, has shown that 0.25% inclusion of turmeric powder in the diet of broiler chickens, significantly increased weight gain at five weeks.

2. Antimicrobial and coccidiostatic activity

Phytobiotics can selectively influence microorganisms through antimicrobial activity, or by a favoruable stimulation of the eubiosis of the microflora. This leads to better utilization and absorption of nutrients resulting in higher performance.

Various plant extracts, especially essential oils, have been studied for their antimicrobial properties. Most research carried out in this area has been conducted in vitro, but there have been a few studies with live poultry flocks.

Phytogenic substances derived from oregano (Origanum vulgare), especially the major active substances thymol and carvacrol, are known to exert antimicrobial and bacterial actions in vitro, while eugenol, a component of the essential oil from cloves, has been shown to inhibit Salmonella typhimurium. Blends of oil containing thymol, eugenol, curcumin and piperin could be used to control Clostridium perfringens, the bacterium that causes necrotic enteritis in broiler chickens.

Essential oil from cinnamon has been shown to improve the digestibility of nutrients in poultry, while polysaccharides from mushroom (Tremella fuciformis) and the herb Astragalus membraneaceus have demonstrated promises responses in controlling experimental coccidial infections.

Directorate of Poultry studies into the effects of turmeric found that the addition of 0.2% to broiler diets resulted in a significant reduction in Escherichia coli count.

Table 1: The effect of turmeric on microflora count 

3. Stimulation of the immune system

Polysaccharides derived from many plants play an important role in stimulating the growth of immune organs, such as the spleen, thymus and bursa, increasing the number and activities of many interdependent cell types such as T, B lympocytes, macrophages and natural killer (NK) cells, and enhancing cellular and humoral immune response.

Dietary addition of 200 g turmeric per quintal of feed significantly increased antibody production in response to sheep red blood cells inoculation of chickens. The persistency of antibody titre was better in birds fed turmeric in the diet. However, the antibody titre declined rapidly in those birds fed a diet that was not supplemented with turmeric.

4. Antioxidant activity

Rosemary, and its extract, is well known as a powerful antioxidant. Similarly, extracts from olive leaf or olive oil can be used as effective antioxidants.

One of the major roles of phyto-antioxidants in poultry production is on lipid oxidation in meat and meat products. Plant oils containing natural antioxidants contribute to the improved oxidative stability of meat and meat products containing higher levels of polyunsaturated fatty acid. These antioxidants are manily tocopherols, however phenols, present in appreciable amounts in olive oil, are effective non-tocophenol antioxidants.

A greater understanding of the relationship between diet, health and stress alleviation in birds is increasingly called for. With the growing ban on the use of antibiotics as routine feed additives, greater focus is being given to nutritional alternatives. This could be accomplished through greater use of alternative NGPs and phytobiotics may be one option.