Quality and stability of an essential oil-based phytogenic emulsion during storage

An important challenge in livestock and poultry farming remains the prevention and treatment of diseases of various etiologies. Due to the WHO-imposed restrictions on antibiotic use, there is an active search for natural phytogenic alternatives. In the rearing of young cattle, serious problems arise during the post-weaning period. In most cases, a complex mixture of natural plant components, including essential oils, or a mixture of only essential oils is used as a feed additive for calves. We have developed a low-component phytogenic liposomal emulsion containing 10 % essential oil (either coriander Coriandrum sativum L. or fennel Foeniculum vulgare Mill.). The emulsion form of the preparation overcomes the inherent hydrophobicity of essential oils, allowing for uniform distribution in a liquid medium. This study presents, for the first time, data on the efficacy of a liposomal emulsion containing essential oil as a phytogenic additive in milk replacer for calves during the milk-feeding period. Our objective was to evaluate the stability of the liposomal emulsion in terms of the quantity and compositional profile of the essential oil during storage and to assess the effect of the phytogenic emulsion on the immune system of calves during the milk-feeding phase. The study material consisted of two variants of phytogenic liposomal emulsions (with soy lecithin as the emulsifier): an emulsion containing coriander ( C. sativum ) essential oil and an emulsion with fennel ( F. vulgare ) essential oil. The essential oil content in the emulsion was 10 % of the total mass. The essential oils were derived from commercial fruits of these crops cultivated at the Selection and Seed Production Center for Essential Oil Crops of the Research Institute of Agriculture of Crimea. The emulsions were prepared on September 1-2, 2023. After preparation, they were dispensed into sealed 15 mL graduated containers and stored under laboratory conditions at 20-22 °C. The content and compositional profile of the essential oils were analyzed monthly over six months (2023-2024). Essential oil extraction from the emulsion was performed via hydrodistillation using the Ginsberg method. The component composition of coriander and fennel essential oils, both extracted from fruits and from emulsions, was determined by gas-liquid chromatography using a Crystal 5000.2 system with a flame ionization detector (ZAO SKB Chromatek, Russia). A microbiological analysis of the emulsions was also conducted using standard methods to detect microbial contamination. The efficacy of the phytogenic emulsions was evaluated in 2023 on Black-and-White dairy calves ( Bos taurus ) during the milk-feeding period at the All-Russian Research Institute of Animal Physiology, Biochemistry, and Nutrition. The calves' basal diet consisted of 750 g of dry milk replacer per animal per day, 150 g of starter feed per animal per day as a supplement, and alfalfa hay. The calves were housed in individual pens until three months of age. Four groups of 10 calves each were formed. Starting at three weeks of age, the milk replacer of three experimental groups was supplemented with an emulsion mixture of fennel and coriander essential oils at a dose of 10 ml/animal (containing 1 mL of essential oils in varying ratios). The experiment lasted 67 days until the calves reached three months of age. At the end of the trial, blood was collected from the jugular vein using an Improvacuter vacuum blood collection system (GIMI, China). Gene expression analysis of I L-6 , IL-8 , and SIRT3 was performed using real-time PCR with original primers and DNA probes ensuring specific reverse transcription and amplification. Relative expression was calculated using the 2-ΔΔCt method. It was found that the essential oil content decreased by 2.7-4.0 % of the initial volume over six months of storage due to the loss of highly volatile components. Consequently, the proportion of major components(linalool in coriander oil and anethole in fennel oil) increased by an average of 4.9 % compared to the pure essential oil (control) used for emulsion preparation. However, their actual content in 15 ml of the respective emulsion remained nearly constant: on average, 1.029±0.011 mL of linalool and 1.071±0.017 mL of anethole, which did not differ from the 1.5 ml of the original essential oil (control: 1.022±0.002 and 1.049±0.006 ml, respectively). Microbiological analysis confirmed the absence of microbial contamination in the emulsions, even after one month of open storage, consistent with the known antibacterial and antimicrobial properties of coriander and fennel essential oils. The inclusion of phytogenic emulsions based on coriander and fennel essential oils in milk replacer positively influenced not only the activation of interleukins associated with humoral immunity but also proteins involved in metabolism.