Essential oils are a blend of highly volatile aromatic molecules with a complex composition, obtained through extraction from plants and their derivatives.
From a chemical standpoint, essential oils can vary in their composition.
Each molecule that makes up the essential oil gives a specific effect to a well-defined biological effect of the essential oil itself.
For example, carvacrol and thymol, the main components of essential oils extracted from plants in the Lamiaceae family (oregano, thyme, rosemary, etc.), are attributed with significant antibacterial properties demonstrated in vitro. Meanwhile, p-cymene, which is present in smaller concentrations, does not have its own antimicrobial effect but is credited with facilitating the transport of thymol and carvacrol through the pathogen’s plasma membrane, contributing to the antimicrobial effect of the essential oil.
The antimicrobial power of carvacrol and thymol is related to their ability to disrupt the stability of cellular membranes, leading to the collapse of the membrane itself with subsequent loss of intracellular contents and thus the death of bacterial cells.
Despite being very similar molecules with recognized antimicrobial roles, the different positions of functional groups in their molecular structures confer different effects on gram-positive or gram-negative bacteria.
ESSENTIAL OILS AND ANIMAL NUTRITION
The use of essential oils in animal feed to support intestinal health has proven to be one of the most important applications of these substances.
Some essential oils, especially those derived from spices like cinnamon essential oil, promote food digestion by stimulating the production of bile and digestive enzymes.
Zeng et al. conducted a study on diets for weaned pigs, comparing the performance of animals fed a standard energy diet (3,400 kcal/kg) to those fed a low-energy diet (3,250 kcal/kg) supplemented with either 0 or 0.25 g/kg of cinnamon and thyme essential oils (4.5% cinnamaldehyde and 13.5% thymol).
The performance observed in pigs fed a low-energy diet supplemented with essential oils, in terms of weight gain, was very similar to that of pigs fed a standard energy diet and significantly better than that recorded in pigs fed a low-energy diet without supplementation.
The addition of essential oils has improved the digestibility of dry matter and crude protein, enhancing performance.
The positive effects of essential oils on digestibility contribute to maintaining intestinal health as improved digestion prevents the accumulation of fermentable substances in the intake that can be used by potentially pathogenic bacteria to proliferate, leading to dysbiosis and intestinal functional disorders such as diarrhea, etc.
ESSENTIAL OILS AND THE EARLY POST-WEANING PERIOD
Several studies investigating the modulatory effect of essential oils on intestinal ecology have been conducted during the early post-weaning period of piglets.
The supplementation of essential oils during this delicate period has proven useful in countering the negative effects that the transition from a liquid to a solid diet induces.
Improper nutritional management can indeed lead to scenarios such as the proliferation of pathogenic bacterial species and the onset of post-weaning diarrhea.
The ability to modulate intestinal bacterial flora, combined with the antioxidant action of the aromatic molecules contained in essential oils, which help counteract the production of free radicals due to the stress caused by the dietary change, has proven to be useful effects in supporting this transition period.
ESSENTIAL OILS AND SOW NUTRITION
The inclusion of essential oils in pig diets has also been studied for their use in sow diets, to test their beneficial effects on reproductive performance.
In general, their use has been found to be useful in stimulating the sow’s appetite and in improving feed utilization due to favorable changes in intestinal ecology.
Although these changes may seem minor, they result in improved animal welfare and less weight loss of the sow during the first week of lactation.
ESSENTIAL OILS AND THE IMMUNE SYSTEM
The close connection between the microbial populations that make up the gut microbiota and the immune system of the animal is increasingly studied and proven.
It is therefore not surprising that there is a correlation between changes in the gut microbiota induced by essential oils and changes in the distribution of lymphocytes at the intestinal level.
The gastrointestinal tract is closely connected to what is defined as gut-associated lymphoid tissue (GALT), which has the largest mass of lymphoid tissue in the animal body and plays a critical role in preventing the entry of common pathogens.
Modulation of the intestinal microflora would result in a reduced need for immune defense at the intestinal level, with a lower distribution of lymphocytes at this site.
A lower immune pressure at the intestinal level could also contribute, at least in part, to the distribution of essential nutrients for the animal’s development rather than for immune defenses.
Additionally, various parameters indicating the animal’s immune status, such as the number of circulating lymphocytes, the phagocytic rate, and the number of immunoglobulins produced, can be modified by integrating the diet with essential oils.
Such modifications are dosis dependent and can vary depending on the more or less pronounced synergistic action that may occur between the different components of the essential oils used.
