Essential oils in poultry feeding. 2. Hypotheses of modes of action implicated

Abstract

The components of essential oils may have various biological activities, i.e. antimicrobial, antioxidant, and stimulant of specific receptors. In animals, their action depends on their fate in the body after feeding, and their biological targets. The absorption site along the digestive tract is modulated by various factors such as diet chemical composition, their form of presentation (free or protected by encapsulation) and dose level. Depending on their absorption site, they can act at various levels: for compounds absorbed in the upper part of the digestive tract, they can act at the systemic level, and for those attaining the end of the small intestine, they can act in digestive contents until this intestinal segment, and at the systemic level after their absorption. The adsorbed products, undergo metabolic changes in the liver, and then act on various organs of animals. After their excretion by kidneys, and due to refluxes from urine to caeca in birds, the compounds generated from essential oils may act on these two blind sacs. They can act on digestive microbiota (precaecal or caecal), animal tissues , that is on their oxidative status, immunity and particularly on inflammation, the digestive tract and its digestive functions, and on animal metabolism, nervous system and behaviour. These compounds have thus a great potential of action, which need to be further studied in the future, in order to optimise their use.