The public concerns associated with the use of antibiotics in poultry production necessitates research into market perceived acceptable natural alternative compounds that promote feed efficiency and food animal health while reducing the burden of foodborne disease. Stepping back from the refined pharmacological fungal metabolites traditionally used in animal agriculture, plant secondary metabolites and essential oils are an attractive avenue of development for poultry production [1]. Research indicates bioactive natural compounds can decrease the microbial burden on the immune system and promote feed efficiency by improving digestibility and gastrointestinal (GIT) morphology in poultry [2–4]. Essential oils and other natural compounds have been documented to possess antibiotic, insecticidal, therapeutic, anti-inflammatory, and chemotherapeutic effects [1, 5].
Further refinements and extrusions of these compounds result in the development of pharmacological agents. Specifically, modifications to these isolated compounds result in known pharmacological agents and antibiotic potentiators [6]. For instance, isoflavones isolated from Lupinus argentus act as potentiators of the α-linolenic acid class of antibiotics, with documented increase in berberine and norfloxacin efficacy which is theorized to occur by the natural plant compound acting as a partial efflux pump antagonist [6]. The benefit of using crude essential oils and other natural compounds is that bioactive compounds are generally regarded as safe and can be multi-modal in their activation effects [1, 5, 7]. Previous research has documented the positive effects of essential oils on poultry production, gut health, and disease resistance [2, 8, 9].
The microbiota actively participates in homeostatic function, nutrient digestion, and biotransformation of compounds. The symbiotic relationship between host commensal microorganisms and the immune system facilitate immune tolerance and development and can have peripheral consequences to overall health and food animal feed efficiency [10–13]. Additionally, as the microbiota directly interact with feed matrices, any potential natural compounds must not negatively disrupt microbiota community structure and stability. Chemical disruption to the microbiota by antibiotic administration can result in a reduction of pharmacological activity of essential oils, enzymes, and other compounds [13–16]. This is important as the biotransformation of chemical compounds by the microbiota can result in the activation of antibiotics, potentiators, and may reduce the efficacy of essential oils and metabolites [14–16]. Sufficient evidentiary support must therefore demonstrate that the microbiota does not render the natural compounds inert nor that the biotransformation results in bactericidal effects that reduce diversity that corresponds with decreased absorption of nutrients and compounds [14–16].
Compartmentalization, or localization to a particular section the GIT, is important, though often overlooked in poultry feed amendment studies [17]. The activity of natural compounds should result in changes to the compartment of activity which would provide knowledge related to the changes within the microbial community structure and may ultimately provide insight into the biology driving these effects. Numerous microbiota studies have focused on the ceca, which may not be ideal as digestion also occurs in the foregut [18, 19]. Evidence suggests that the jejunum of feed-efficient animals, which is the site of nutrient absorption, has improved morphology, and increased enzymatic activity [20]. Likewise, the ileum, which absorbs any remaining vitamins and other nutrients not absorbed in the jejunum, is lighter and longer in more feed-efficient animals, with improved morphology [20]. While the ceca are heavily focused on in other studies with natural compounds and for the microbiota responses, it may not necessarily be the site biological activity occurs nor the site with the most biological ramifications if the microbial populations change [16, 17, 20]. Additionally, as microencapsulation technology continues to evolve, the targeted delivery of natural compounds through the harsh environment of the crop to their intended further location down the GIT may serve to improve biological activity [21].
There are numerous studies in the literature that evaluate the role of essential oils and other natural products. For example, thymol has been evaluated for its anti-inflammatory and microbiota modulating effects in poultry with promising results [22] and vanillin has been shown to exhibit antibiotic-like effects [23, 24]. Organic acids have also shown promise as a feed amendment in poultry [25]. Sorbic acid has anti-fungal properties and combined with prebiotics can improve feed efficiency [26, 27] while citric acid can be used as an antimicrobial in food processing and has minimal effects in vivo when included at high concentrations [28]. In another study, citric and acetic acid combinations improved body weight gain, feed conversion, and feed efficiency at a lower inclusion rate [29].
The objectives of this study were to evaluate the effects of feeding broilers a diet supplemented with a microencapsulated blend of organic acids (25% citric and 16.7% sorbic), and botanicals (1.7% thymol and 1% vanillin; AviPlus®P) on the microbiota populations in the jejunum and ileum. Broilers were used because the real-life effects of these compounds in production animals are an important research question to ask in order to determine the mechanism of action. The commercial broiler by-product chickens used in this study are representative of the birds used in poultry production. These two tissues were selected because they are two important organ systems associated with feed efficiency and production in broilers. Only organ specific effects can truly be delineated using in vivo models. By evaluating community structure and composition, it will be possible to determine if there are any effects on the microbiota due to bioactivity of organic acids and botanicals.