| Unlocking the potential of essential oils: Enhancing egg production and quality in poultry diets.
There is a growing demand for natural alternatives in poultry feed. These alternatives must not leave residues in animal-derived products and should exhibit similar enzymatic activity to synthetic products. Among the options are probiotics, prebiotics, essential oils, and organic acids, among others (Catalan et al., 2012).
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Essential oils contain volatile, lipophilic, and low molecular weight compounds. These substances are derived from the secondary metabolism of plants, which, while not directly linked to the plant’s survival, enhance adaptability to environmental conditions, providing an evolutionary advantage.
They can be extracted through steam distillation, hydrodistillation, or expression of citrus fruit pericarps. Other methods include enfleurage, supercritical CO2 extraction (commonly used in industry), and non-polar organic solvents (Jorge, 2009).
Due to their volatility, active compounds are sensitive to environmental factors such as oxygen, light, heat, and humidity, making them prone to oxidation and degradation. For industrial applications and animal feed, it is essential to develop techniques that protect and preserve their key properties, such as microencapsulation (Hall et al., 2020).
Encapsulation was developed to achieve stabilization, solubilization, and controlled release of compounds. It is a process in which a specific material is surrounded or coated by another material or a combination of materials.
In essence, it is a mechanism for packaging, separating, and storing substances in microscopic capsules for subsequent release, enabling greater utilization of the encapsulated components (Gonçalves et al., 2017).
Therefore, the use of essential oils in monogastric animals, when added to feed, has shown positive results, particularly in:
- Improving nutrient digestibility by maintaining eubiosis (a healthy balance of gut flora) in the gastrointestinal tract (Amad et al., 2011).
- Exhibiting antimicrobial activity by reducing pathogenic bacteria (Alhajj et al., 2015).
- Enhancing feed intake, increasing digestive secretions, and supporting the body’s antioxidant activities (Fonseca et al., 2015).
Oxidative stress occurs when there is an imbalance between the generation of oxidant compounds and the action of antioxidant defense systems, which can be either enzymatic or non-enzymatic.
The generation of oxidant compounds (free radicals) typically occurs in the mitochondria, cell membranes, and cytoplasm, with the mitochondria, through the electron transport chain, being the primary source. This is because, to produce energy (ATP), there is a progressive and complete reduction of oxygen (O2), resulting in the formation of two molecules of water (H2O).
When the reduction occurs partially, unpaired electrons are formed, which have the ability to cause oxidative damage, known as free radicals (Barbosa et al., 2010).
However, the term free radical is not the ideal term for the group of pathogenic reactive agents, as some of them do not have unpaired electrons in their outer shell, although they are involved in oxidation-reduction reactions.
Therefore, the terms reactive oxygen species (ROS) and reactive nitrogen species (RNS) are considered more appropriate, as they better describe these oxidant compounds (Vasconcelos et al., 2014).
| Since oxygen is extremely important for cells to obtain energy through metabolic reactions, the production of ROS and RNS always occurs and is considered a normal physiological process, as long as it is generated in small amounts (Halliwell & Gutteridge, 2015). |
This reactivity of oxygen and the resulting toxicity to the organism led to the development of antioxidant defense mechanisms in the system itself, which include enzymes such as Superoxide Dismutase (SOD), Catalase (CAT), and Glutathione Peroxidase (GPx), aimed at maintaining oxidative homeostasis and ensuring cell survival. However, the body cannot guarantee defense on its own, so it is necessary to use non-enzymatic antioxidants to contain the spread of oxidation (Augustyniak et al., 2010).
An antioxidant is described as “any compound present in low concentrations, compared to others, that significantly delays or prevents the oxidation of oxidizable substrates.”
Such substances can act directly by neutralizing the action of free radicals, or indirectly by participating in enzymatic systems with such capacity.
Antioxidants can be characterized as either synthetic (industrially produced) or natural (phenolic compounds found in plant-derived products) (Ramalho & Jorge, 2006)
Among the plant-derived compounds are essential oils from red pepper, cinnamon, and oregano.
Cinnamon (Cinnamomum verum) is an evergreen tree, with the inner bark of its trunk being rich in essential oil primarily composed of the active ingredient cinnamaldehyde, while the leaves are a source of eugenol.
However, although there are several studies in the area using essential oils and oleoresins for poultry, there are still discrepancies in the results obtained, mainly due to factors such as:
- The type and part of the plant used and its physical properties;
- The harvest time;
- The method of preparation of the phytogenic additive;
- Compatibility with other feed ingredients and the level of supplementation in animal diets;
- Additionally, results also vary based on the extraction processing technique of the oil and the type of laboratory analysis conducted by the researchers (Yang et al., 2009; Paschoal et al., 2014).
To address this, the GENCO research group at the Universidade Estadual de Maringá (UEM) conducted studies aimed at evaluating the addition of essential oils for laying hens from the rearing phase to the early laying phase (35 weeks).
An experiment was conducted with five experimental diets:
- (T1) Control: 0 mg of essential oil/kg of diet;
- (T2) 100 mg/kg of essential oil mixture;
- (T3) 200 mg/kg of essential oil mixture;
- (T4) Residual mixture 100 mg/kg during the rearing and growth phases;
- (T5) Residual mixture 200 mg/kg during the rearing and growth phases.
During the laying phase (20 to 35 weeks of age), the birds in treatment 1 were only given the basal feed during the rearing and growth phases. For treatments 2 and 3, the birds received the same treatment during both the rearing and growth phases. In treatments 4 and 5, the birds received the essential oil mixture during the rearing and growth phases but did not receive it during the 20 to 35-week period. The mixture consisted of: Capsaicin oleoresin (red pepper) + Cinnamaldehyde (cinnamon) + Carvacrol (oregano).
As a result, no significant differences were observed for the performance variables evaluated: initial body weight, final body weight, daily feed intake, egg production rate, feed conversion per kilogram of eggs, and feed conversion per dozen eggs, among the treatments.
For the egg quality variables evaluated, including Haugh unit, specific gravity, shell thickness, yolk percentage, albumin and shell, yolk and albumin index, no significant differences were observed between treatments. However, for egg weight, there was a significant difference, with treatments 1, 2, and 3 showing higher egg weight compared to treatments 4 and 5.
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