Antibiotic growth promoters have been used widely in livestock production for almost 50 years. The potential health risks and environmental problems caused by the excessive use of synthetic pharmaceuticals including antibiotics as growth promoters, the public demand for organic foods have gradually increased. Investigations on use of antibiotics as growth promoter in animals resulted an increased incidence of microbial resistance among human pathogens due to continuous use of antibiotics as growth promoter in animals. That led to ban on using antibiotic growth promoters in livestock feeding in developed countries at early 2000s. Exclusion of antibiotics as growth promoters in animals significantly increased the incidence of infection by pathogens, consequently having detrimental effect on the performance of commercial animals in terms of economic return to the farmers. Therefore, the trend of finding available alternatives was increased.
Research has focused on the development of alternative strategies to maintain animal health and enhance performance, numerous substances commonly known as natural growth promoters have been identified as effective alternatives to antibiotics. Phytobiotics are among the natural growth promoters that have been raising in popularity as feed additives, due to their benefitical effect on gut health, immunity and growth performance. Phytobiotics or botanicals phytogenics are plant-derived products used in feed to potentially improve performance of animals. Aside from having antimicrobial activity, phytobiotics potentially provide antioxidative effects, enhance palatability, improve gut functions, or promote growth. Phytobiotics includes a wide range of plant-derived products such as essential oils, herbs and oleoresins that can be added to the diet of commercial animals to improve their productivity through enhancing feed quality, promoting animal’s performance, and improving the quality of products derived from these animals. Phytobiotics derived from different phytogenic compounds can be classified based on their origin and processing, including herbs (flowering, non-woody and non-persistent plants), spices (herbs with an intensive smell or taste commonly added to human food), essential oils (volatile lipophilic compounds) and oleoresins (extracts derived by non-aqueous solvents).
Ways of phytobiotics to produce their beneficial effects:
- Feed intake: Phytogenics increase feed intake due to the claimed improvement in palatability of the diet resulting from the enhanced flavor, especially with the use of essential oils. However, the effect on feed intake of adding essential oils to diets is highly variable. Some studies reported decreased feed intake with increasing inclusion levels of the phytogenic substance used. Phytobiotics initiate its activity in the feed as flavour and, therefore, influence eating patterns, stimulation of digestive secretions, including saliva, digestive enzymes, bile and mucus is often considered to be one of the important actions of phytobiotics.
- Anti-oxidative and anti-inflammatory: Anti-oxidative properties of phytogenic substances have been attributed to the phenolic terpenes in the essential oils. Essential oils of plants belonging to the Labiatae family have been widely used as antioxidants in human and pet foods. Plants high in terpenes include rosemary, oregano, and thyme. However, whether they can be added in required amounts to replace the effects of antioxidants commonly used in pig diets, such as ethoxyquin and butylated hydroxytoluene. 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.
- Antimicrobial effect: 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.This property is mainly attributed to the essential oils of these plants. Oregano and thyme are among those which have received a great deal of interest. These plants contain the monoterpenes carvacrol and thymol, respectively, and have demonstrated high efficacy in vitro against several pathogens found in the intestinal tract. This suggests that phytogenic feed additives may be suitable replacements for in-feed antibiotics to improve monogastric animal’s health and growth performance. 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.
- Stimulation of the immune system: Polysaccharides derived from plants play an important role in stimulating the growth of organs, such as the spleen, thymus and bursa, increasing the number and activities of immune cells such as T, B lympocytes, macrophages and natural killer cells, and enhancing cellular and humoral immune response.
Different aspects of phytobiotics have been studied in the last two decades. Growth promoting effect, antimicrobial activity, antioxidant activity and anti-inflammation activity are some of the functions that have been investigated. According to the literature, phytobiotics have positive effects in improving the performance of poultry and swine. Some researchers have suggested that the improving effects of dietary supplementation with PFA are partially associated with enhanced feed consumption probably due to improved palatability of the diet. Regarding the antimicrobial activity, there is some evidence supporting the assumption that the general mode of action of PFA is by modulating gut microflora and reducing intestinal pathogen pressure. Comparing antimicrobial feed additives and organic acids with PFAs that are currently being used in poultry and swine feed, shows similar modulation effects for relevant gastrointestinal factors such as microbiota, fermentation products (including undesirable or toxic substances), nutrients digestibility, gut tissue morphology, and reactions of the gut-associated lymphatic system.