SPECIAL STORY 74 FEED & ADDITIVE MAGAZINE April 2023 monitoring the effect after ND vaccination (Graphic 1). IgA is essential for promoting local immunity in the respiratory and gastrointestinal tracts. In addition, lower levels of the liver enzymes AST and ALT, which can indicate liver stress and liver cell damage, were measured. A reduction in these enzymes suggests that this combination of EOs may help to reduce the stress and damage to the liver caused by these vaccines. They also showed that daily administration of this specific blend of EOs as a spray and in drinking water resulted in a strong immune response. Similar results were observed and summarised by Peterfalvi et al. (Molecules, 2019). There it is quoted that "in broiler chickens, dietary supplementation with a mixture of thyme (Thymus vulgaris), peppermint (Mentha piperita) and eucalyptus (Eucalyptus globulus) EOs [in a specific ratio] at increasing doses linearly increased serum antibody titres to ND, IB and bursal disease viruses on day four after vaccination. On the eighth day after vaccination, antibody titres were significantly higher at certain EO blend doses compared to the control group." In addition, the EO blend containing eucalyptus oil, mint oil and thyme oil plus L-menthol has also been shown to have a positive effect on the respiratory system, reducing respiratory symptoms following vaccination against respiratory diseases [2]. It should be noted that there is still a lack of research on combinations of vaccines and EOs. Some combinations of EOs and vaccines may even have the opposite effect, causing undesirable cross-interactions. Therefore, an appropriate safety interval is recommended. 5. Essential oils and their effect on the digestive system In addition to its effects on the respiratory system, the combination of natural EOs mentioned above is said to improve the balance of the microbiome in the digestive system and have a positive effect on the morphological development of the gut. Working positively on the characteristics of the digestive system can lead to increased nutrient absorption, which in turn can positively stimulate a stronger overall immune response. A study published in 2019 by Nameghi et al.[4] suggested that "supplementation of drinking water with a mixture of essential oils (EOB) derived from thyme, peppermint and eucalyptus […] could improve growth performance, humoral immunity and ileal morphology and microflora in broilers", thus representing "an alternative to antibiotic growth promoters". It is worth recalling the interaction between the gastrointestinal tract (GIT) and the respiratory tract. Although they are separate organ systems, both are part of a common mucosal immune system, known as the research concept of the gut-lung axis (Budden et al, 2016) and therefore it must be considered that these organ systems are connected and influence each other. Own field trials in pigs and calves have also shown similar beneficial effects of EO blends on both digestive and respiratory organ systems. Graphic 1. Adapted from "Thajel and Ulaiwi, et al., 2017. Development of IgA concentration (mg/dl) in chicken of selected groups at day 15, 25 and 35 of trial [2]. G1: 30 chicken, drinking water application of 0,2 ml/L Aromax® + drinking water application NDv vaccine. G4: 30 chicken, spray application of (2 ml/L) Aromax® twice weekly + drinking water application (0.2 ml/L) Aromax® daily + spray vaccination NDv. G7: 30 chicken, drinking water vaccination NDv (control group).
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