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).
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.