Antioxidants in feed for laying hens

Christine Laganá

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The inclusion of lipid sources in diets for laying hens is a common practice, as they increase energy density, improve feed conversion and palatability, facilitate the absorption and digestion of non-lipid components, and serve as a source of essential fatty acids.

In addition to the previously mentioned functions, lipids have roles in the body that are carried out exclusively by them.

Most lipid synthesis in birds takes place in the liver. Since lipogenesis occurs almost exclusively in the liver, birds are more prone to metabolic disorders such as hepatic lipidosis (Bertechini, 2012).

The addition of oils or fats to the diet as a source of unsaturated fatty acids is essential for achieving proper nutrition and production (Nogueira et al., 2014).

During the pre-laying period, pullets reduce their feed intake due to the metabolic stress of production, which suggests the need to increase energy levels in the diet so that the bird can build up reserves for egg production.

Stress affects the physiology of birds at all stages of rearing, triggering metabolic oxidation reactions that, when elevated, impair performance and increase susceptibility to disease, as oxidative stress disrupts immune system function (Souza, 2022).

An important fact, common to non-ruminant animals, is that the fatty acid profile of the diet directly influences the lipid profile deposited, both in the carcass and in the eggs.

Eggs are considered one of the most complete foods, as they are not only a natural, low-cost source of protein, but also contain fats, vitamins, and minerals, while being low in calories.

They are an important reservoir of health-beneficial nutrients and play a preventive role against diseases, contributing to antibacterial and antiviral activities, as well as modulating the immune system (Amaral et al., 2016).

Due to their rich composition of essential fatty acids, eggs are prone to lipid oxidation immediately after being laid.

According to Amensour et al. (2010), although oxidative processes are not considered an obstacle, when ingredients rich in unsaturated fatty acids are added to the diet, egg production is enriched with these long-chain fatty acids, which may increase susceptibility to oxidative deterioration, affecting egg quality and resulting in the production of toxic compounds.

Oxidation is a mechanism that can occur in plant and animal tissues and their by-products, such as fats and oils.

Catalysts such as light, heat, free radicals, metal ions, and pigments induce a complex process called lipid oxidation in the presence of oxygen (Laguerre et al., 2007).

Lipid oxidation during food processing and storage is of great importance. As polyunsaturated lipids oxidize, they form hydroperoxides, which are susceptible to further oxidation or breakdown into secondary reaction products such as short-chain aldehydes, ketones, and other oxygenated compounds that can negatively affect the overall quality of the food, including aroma, flavor, nutritional value, and the production of toxic compounds (Vercellotti et al., 1992).

Exposure to light, storage conditions, processing, time, and temperature of the egg can cause oxidative damage.

The use of antioxidant compounds present in the diet or even synthetic ones is one of the defense mechanisms against free radicals. These antioxidants can be used in the food, cosmetic, beverage industries, and medicine, as many medications often increase the intracellular generation of these radicals (Doroshow, 1983; Halliwell et al., 1995; Weijl et al., 1997).

The current market seeks to guarantee the reliability of products generated by animal-origin food production chains through international certifications and regulations, which even consider animal welfare as a policy of responsibility for food quality and safety.

In response, there have been advances in research aimed at including viable alternative products in the diets of laying hens, such as plant extracts (Fukayama et al., 2005) and vitamins, which have demonstrated antimicrobial and antioxidant effects and promote improvements in animal performance and immune response (Brugalli, 2003).

Minerals such as selenium, copper, zinc, manganese, and iron, along with vitamins C, E, and A, and carotenoids like beta-carotene, lycopene, and lutein, as well as tannins such as catechins, are notable for their role in defending against oxidation (Halliwell & Gutteridge, 1999).

Compounds found in plant cells—including lycopene, xanthin, beta-carotene, lutein, cryptoxanthin, zeaxanthin, and astaxanthin—which are precursors of vitamin A, also act as antioxidants. They can oxidize oxygen radicals, which is essential for neutralizing these harmful molecules (Valduga, 2009).

Phenolic substances are products of the secondary metabolism of plants and are found in plant tissues, both in free form and bound to sugars and proteins. These compounds have antioxidant properties, as they act as redox agents, contributing to the neutralization of free radicals in the body (Silva, 2010).

With the aim of improving poultry performance and egg quality through their antioxidant activity, many studies have been conducted on the inclusion of plant-based compounds in layer hen feed.

Radwan et al. (2008) found that the inclusion of oregano, rosemary, thyme, or saffron in layer hen diets can improve productive performance, enhance oxidative stability of eggs, and reduce yolk lipid oxidation during storage.

Özeku et al. (2011) reported a significant improvement in albumen height and Haugh unit values in eggs from hens fed a mixture of essential oils including oregano, bay leaf, sage, myrtle, fennel, and citrus.

Zhao et al. (2011) concluded that adding ginger powder to layer diets increased egg mass production and improved lipid stability in both feed and eggs during storage.
Freitas et al. (2013) found that supplementing diets with either synthetic antioxidants or ethanolic mango extracts led to improvements in albumen quality and lipid stability of the eggs.

Papadopoulou et al. (2017) observed that the inclusion of polyphenols derived from olives, administered via drinking water, helps reduce damage induced by oxidative stress in poultry.

Zhou et al. (2021) found that supplementation with tea polyphenols (600 mg/kg) can partially alleviate adverse effects of oxidative stress. This was reflected in:

an increase in antioxidant enzyme activity,

upregulation of genes related to antioxidant defenses in laying hens, and

an increase in free amino acids in the yolk.

Other compounds, such as passion fruit seed oil, which is rich in tocopherols, phytosterols, carotenoids, and phenolic compounds, and known for protecting the body against oxidative agents, have been investigated for their antioxidant action (Da Silva & Jorge, 2017).

Plant extracts and essential oils have long been used in human medicine, and more recently, they have been explored in animal production for their potential benefits.

The use of phytogenic feed additives or medicinal plants in animal nutrition has recently received increased attention as alternatives to traditional antibiotics, probiotics, and prebiotics. These natural solutions are undoubtedly emerging as a healthy and sustainable option for high-quality poultry production in the near future.