Essential Oils as a Feed Additives: Pharmacokinetics and Potential Toxicity in Monogastric Animals

Abstract

Essential oils (EOs) are now a hot topic in finding modern substitutes for antibiotics. Many studies have shown positive results and confirmed their high antibacterial activity both in vitro and in vivo. Deservedly, there is an attempt to use EOs as a substitute for antibiotics, which are currently limited by legislation in animal breeding. Given the potential of EOs, studies on their fate in the body need to be summarized. The content of EO’s active substances varies depending on growing conditions and consequently on processing and storage. Their content also changes dynamically during the passage through the gastrointestinal tract and their effective concentration can be noticeably diluted at their place of action (small intestine and colon). Based on the solubility of the individual EO’s active substances, they are eliminated from the body at different rates. Despite a strong antimicrobial effect, some oils can be toxic to the body and cause damage to the liver, kidneys, or gastrointestinal tissues. Reproductive toxicity has been reported for Origanum vulgare and Mentha arvensis. Several publications also address the effect on the genome. It has been observed that EOs can show both genoprotective effects (Syzygium aromaticum) and genotoxicity, as is the case of Cinnamomum camphor. This review shows that although oils are mainly studied as promising antimicrobials, it is also important to assess animal safety.

Immunomodulatory Activities of Selected Essential Oils

“…The geographical origin, environment, and extraction parameters highly affect the final extract composition. Variations in the main composition, but also changes in minor substances, can lead to great variations, representing a challenging task for commercial exploitation and exploration [ 81 , 82 ]. Chemometric approaches might reliably predict the bioactivity of multicomponent substances in the future for better characterization of EOs and an improved comparability within studies [ 8 , 9 ].…”

Diet supplementation with thyme oil and its main component thymol failed to favorably alter rumen fermentation, improve nutrient utilization, or enhance milk production in dairy cows

“…The in vitro dose of 500 mg/L applied by Castillejos et al (2006) would correspond to an intake of 50 g/d of thymol, assuming a rumen volume of 100 L for an average adult dairy cow. Such an amount is too high and is impractical for use in live animals because it has adverse effects on feed digestion and fermentation in the rumen (Yang et al, 2010;Patra and Yu, 2012); it is not economically feasible (i.e., high cost of EO); palatability is a problem (Beauchemin et al, 2009;Benchaar et al, 2009); and it may be toxic in animals (Durmic and Blache, 2012;Yang et al, 2015;Horky et al, 2019). Diet supplementation with monensin tended to decrease DMI by 1.2 kg/d, compared with the control diet.…”

Acute, reproductive, and developmental toxicity of essential oils assessed with alternative in vitro and in vivo systems

“…EOs possess manifold bioactive properties and are therefore continuously being tested for various applications such as natural pesticides (Pavela and Benelli 2016 ), food preservatives (Pandey et al 2016 ), alternatives to antibiotics in animal feed (Stevanovic et al 2018 ), compounds in aromatherapy (Reis and Jones 2017 ) and cosmetic ingredients (Sarkic and Stappen 2018 ). However, due to large variations in chemical composition, mainly depending on ambient growth conditions, genetic diversity, and extraction procedures, commercial exploitation and exploration of EOs is difficult (Horky et al 2019 ; Tammar et al 2019 ). This might also be the reason for contradictory findings of EO toxicity in vitro and in vivo.…”

“…However, recent studies generated contradictory findings of the toxicity of EOs in vitro and in vivo, also demonstrating that some EOs already show toxic properties at very low concentrations. Effects such as respiratory disorders, mucous membrane irritation, acute toxicity, reproductive toxicity and organ toxicity were discussed within this regard (Bakkali et al 2008 ; Horky et al 2019 ; Mehdizadeh and Moghaddam 2018 ; Sandner et al 2020a ). Thus, the toxic potential must be first investigated when EOs are intended to be used for therapeutic aims, or being incorporated in cosmetic, food and feed products.…”