Omega-6: Its Pharmacology, Effect On The Broiler Production, And Health

Lipids and oils are the primary sources of monounsaturated and polyunsaturated fatty acids (MUFA and PUFA), which are necessary for human and animal health. Omega-3 and omega-6 are essential nutrients for broilers. Omega-6 members, such as linolenic acid, are essential for broilers and must be obtained through feed. Vegetable oils are the primary source of omega-6 added to broiler feeds. Unsaturated fatty acids are better digested and absorbed than saturated fatty acids and generate more energy at a lower cost, boosting productivity. Feeding supplements with omega-6 can increase the fatty acid content in meat and increase weight, carcass, viscera, and FCR. The quality of meat taste and antioxidant content was also improved after giving omega-6 and influencing mineral metabolism. Broiler reproductive performance is also enhanced by reducing late embryonic mortality, hence enhancing fertility, hatchability, sperm quality, and sperm quantity. Meanwhile, for broiler health, omega-6 can lower cholesterol levels, triglycerides, very low-density lipoprotein, and low-density lipoprotein. It also supports support for helper cell (TH)-2-like IgG titers, increasing prostaglandins, eicosanoids, and antioxidants. In addition, it also supports anti-inflammation. Other researchers have extensively researched and reviewed studies on the effects of omega-6 on poultry. Meanwhile, in this review, we provide new findings to complement previous studies. However, further studies regarding the effects of omega-6 on other poultry are needed to determine the performance of omega-6 more broadly

1. Introduction

The proportion of poultry meat in the average global output of 323.25 million tons (mt) over the past five years was 122.82 million tons (mt) or 37.99% [1]. Also, chicken meat output has increased in developed and developing nations over the past six decades [2]. Moreover, due to its high protein, low-fat content, and tasty favor, chicken is expected to be the most consumed animal protein in the world in 2020. Fat and oil are frequently added to poultry diets to boost their energy density. By selecting minerals and supplements for live birds, it is possible to boost the nutritional value of chicken meat, which is one of its benefits. In recent years, numerous oils have been employed commercially to supply lipids to chickens. Some studies have indicated that supplementing poultry diets with lipids alters feed intake, energy efficiency, the profile of thigh and breast muscles, and broiler meat quality [3–5]. Te supplementation of polyunsaturated fatty acids (PUFAs) can raise the concentration of PUFAs in the carcass. Fatty acids, particularly essential fatty acids, are gaining relevance in poultry feeding systems because they improve birds’ health and productivity. Our health-conscious culture favours well-balanced diets to reduce the risk of unfavorable health effects [6]. PUFA has also boosted the demand for animal diets containing c-linolenic acid [7]. c-linolenic acid (C18 : 3 n − 6) improves chicken health by acting as an anti-inflammatory, antithrombotic, antiproliferative, and lipid-lowering agent by conversion to prostaglandin E1 [8].

Enriching broiler chicken muscles with PUFAs, particularly omega-3 and omega-6 fatty acids, can reduce the risk of cardiovascular disease and protect against atherosclerosis and coronary heart disease by lowering cholesterol and low-density lipoprotein (LDL) levels in the blood and reducing platelet aggregation [9]. However, there is limited research on the particular mechanism of omega-6 in broiler performance. The current article includes an update on the therapeutic qualities of omega-6, as well as its origins, chemistry, biosynthesis, absorption, distribution, broiler production, and health.

2. Data Collection 

Data gathering a search of electronic databases follow a previous report such as PubMed, Elsevier, ResearchGate, and Google Scholar using the keywords “omega-6,” “omega- 6 pharmacology,” “omega-6 absorptions,” “omega-6 for poultry,” “omega-6 for broilers,” “omega-6 for broiler production performance,” and “omega-6 for broiler health.” Selected papers from 2006 to 2022 were chosen based on their content. Relevant articles that used the keywords mentioned previously and were written in English have been included.

2.1. Sources and Chemistry of Omega-6.

Lipids’ physical and chemical properties are dictated by their fatty acid content, carbon chain length, and degree of saturation. Unsaturated denotes the presence of one or more double bonds, whereas saturated indicates the lack of double bonds in chemical structure [10]. Increasing the length of the carbonic chain of saturated fatty acids raises the fat’s melting point, while the presence of a double bond lowers the fat’s melting point [11]. Additionally, the shape of the double bond impacts the melting point. The melting point of trans fatty acids is higher than that of their cis isomers [12].

The acyl chain of polyunsaturated fatty acids has two or more methylene-interrupted double-bond desaturations [13]. PUFAs may also contain a carboxylic acid at one end of the molecule and a methyl group at the other. This structure is named Omega (“Ꞷ ” or “n”) and is subdivided into n − 3, n − 6, n − 7, and n − 9 fatty acids, which correspond to the double bond if unsaturation is present [14]. (n−) indicates the position of the carbon double bond counting from the methyl end. Omega-3 and Omega-6 family members are the nutritionally essential PUFAs for poultry health [15]. As seen in Table 1, there are numerous Omega-6 variants. Palmitoleic acid and oleic acid could be generated in the body via metabolic pathways. However, linolenic acid and linoleic acid are necessary fatty acids that must be ingested [14]. Additionally, high amounts of polyunsaturated fatty acids undergo autoxidation far more rapidly than saturated PUFAs, particularly when exposed to heat, light, oxygen, and transition metals during manufacture, processing, and storage [15, 16]. However, conjugated linoleic acids are sometimes misclassified as omega-6 (abbreviated −6 or n − 6) fatty acids. Conjugated linoleic acids are a class of fatty acids including up to 56 isomers with conjugated (juxtaposed or adjacent) double bond pairs along octadecadienoic (18 : 2) [17, 18].

Typical vegetable oils such as sunflower oil, safflower oil, palm oil, Silybum marianum oil, sesame oil, pumpkin seed oil, peanut oil, wheat germ oil, rice bran oil, linseed oil, and maize oil are sources of n − 6 PUFAs [19–23]. Figure 1 shows sources of n − 6 PUFAs. Te majority of PUFAs in plants and marine foods are cis-configured. n − 6 PUFAs are predominantly composed of linoleic acid (C18 : 2) and arachidonic acid (AA, C20 : 4) [24], whereas linoleic acid might undergo desaturation and elongation to produce arachidonic acid (ARA, 20: 4n − 6) and docosahexaenoic acid (DTA, 22 : 4n − 6) [25]. In addition, Certık et al. [26] identified oleaginous lower filamentous fungi as a rich source of c-linolenic acid. Utilizing these fungi in a solid-state fermentation method generates a bioproduct enriched with c-linolenic acid that can be utilized directly as a chicken feed supplement. However, there are limited c-linolenic acid sources, notably in the plant (e.g., blackcurrant, evening primrose, borage, or hemp seeds). Utilizing solid-state fermentation (SSF) is an alternate method for producing c-linolenic acid from microorganisms. SSF is a prospective bioprocess that combines fungal consumption (Tamnidium elegans, Cunninghamella species, or Mortierella isabelline) of moist solid materials (agricultural byproducts) with the generation of valuable metabolites in a cost-effective manner [27].

2.2. Omega-6 Biosynthesis, Absorption, and Distribution. 

Specifically, long-chain n − 6 and n − 3 PUFAs are regarded as necessary due to the inability of avian species to insert a double bond beyond 19 carbons due to a lack of 1–12 and 15 desaturases; they must be supplied from the food [28, 29]. Long-chain PUFAs are mainly generated in the liver [20]. During the conversion of c-linolenic acid to eicosapentaenoic acid or docosahexaenoic acid and linoleic acid to arachidonic acid, desaturation and elongation of the respective precursors take place in the presence of elongation of very long-chain fatty acids ELOVL2 and ELOVL5, Δ5-desaturase, Δ6-desaturase, and peroxisomal β-oxidation to acquire docosahexaenoic acid (Figure 2.) [12]. However, desaturase enzymes for omega-3 and omega-6 routes are identical [29].

Figure 1: Various plants that contain a high level of omega-6.

Absorbed c-linolenic acid fatty acids and linoleic acid are transferred to adipose tissue and other tissues. In contrast, arachidonic acid is retained more in the liver, duodenum, heart, spleen, brain, and other cells (thrombocytes, peripheral blood mononuclear (PBMN)) [30]. Moreover, long-chain unsaturated fatty acids have more potential to form micelles. They could function synergistically in the absorption of saturated fatty acids (SFA) when combined with saturated fatty acids (SFA). Furthermore, micelles have an estimated particle size between 30 and 40 ˚ A, which is sufficiently tiny to pass between the microvilli of mucosal cells [31]. In monogastric animals, fat absorption occurs between the end of the duodenum and the end of the ileum [32].

On the contrary, when c-linolenic acid-rich oils are consumed orally, c-linolenic acid is readily absorbed and initially appears in serum phospholipids. The substance is then dispersed across different phospholipid fractions following continued dosing. A portion of the c-linolenic acid received is oxidized. The remainder is rapidly lengthened to Dihomo-c-linolenic acid in the plasma, renal artery, liver, and aorta and could also elevate arachidonic acid, although exclusively in the plasma and liver [33]. Dihomo-c-linolenic acid and c-linolenic acid levels in the liver were proportional to the amount of c-linolenic acid present, regardless of the oil source, indicating that oils are efficiently absorbed and that the amount of c-linolenic acid absorbed is dose-dependent [34].

2.3. Effect of Omega-6 in Broiler Production. 

Providing a lipid diet with the required fatty acid profile for the resultant tissue makes it possible to modify the fatty acid profiles of broiler tissues. Velasco et al. [35] showed greater feed efficiency in chicks that received diets rich in unsaturated fat sources than in chicks that were fed diets rich in saturated fat. Moreover, current poultry feed is based on grains with a high ratio of n − 6 fatty acids to n − 3 fatty acids. This feed results in high levels of arachidonic acid (20 : 4n − 6) in meat and egg products and reduced levels of docosapentaenoic (DPA, 22 : 5n − 3), eicosapentaenoic (EPA, 20 : 5n 3), and docosahexaenoic (DHA, 22: 6n − 3) acids [23]. Furthermore, broilers fed diets with high levels of linoleic acid consumed less feed per day than those who received neither a supplement nor diets with low levels of linoleic acid [36].

Omega-6 supplementation shows positive results on broiler performance. Te highest body weight, carcass yield, and FCR were observed when linoleic acid was added to broiler feed [37]. Pirzado et al. [38] also found the same result and observed that broilers’ feed conversion ratio (FCR) values were significantly enhanced after receiving omega-6. With the addition of linoleic acid, a more signifcant concentration of chlorides was also discovered in the chickens’ serum, which may be connected with a higher requirement for the concentration of HCl in the stomach in response to a higher lipid intake and enhanced chloride ion management in the body [39].

Broiler of is also affected by omega-6 supplementation. According to a study by Gaad et al. [36], omega-6 increases the weight of giblets; the liver, heart, and gizzard are much heavier. Moreover, the comparatively high concentrations of n − 6 PUFAs (up to 45.0% in a corn oil diet) made cardiac and hepatic tissues the wealthiest types of fatty acids [40]. In other poultry species, dietary 6% PUFA originated from corn oil in Japanese quail showed increased productivity, follicular hierarchy in the ovarium, and heart weight without harming other visceral organs due to its beneficial effects as an energy and essential fatty acid source, antioxidant, antiparasite, and endocrine hormone precursor [41–43]. Furthermore, the antioxidant capacity of broiler breast meat was enhanced by a diet including c-linolenic acid and linoleic acid, as demonstrated in a prior study [44]. However, Fejerˇc´akov´a et al. [33] discovered that GPx activity evaluated in the liver is essentially unaffected by agrimony and -linolenic acid-containing diets.

Omega-6 can also impact the fat content of poultry. According to research (El-Katcha), excessive treatment with n − 6 fatty acids boosts fatty acid oxidation and hence increases the metabolic rate of animals. Qi et al. [45] observed that dietary n − 6/n − 3 PUFA (10:1) had a substantial effect on subcutaneous and intramuscular fat content as well as meat quality in chickens (color and tenderness). Analysis of the chemical composition revealed that hens fed a meal supplemented with linoleic acid had a higher fat content in the breast and thigh [39]. The addition of linoleic acid to compound feed for broilers, according to another study by Haˇsˇc´ık et al. [46], enhances the intensity of growth and the proportion of internal, subcutaneous, and intramuscular fat. 

Moreover, the chosen cereal product with a greater concentration of c-linolenic acid (3.676 1.09 kg−1 in wheat bran) increased the concentration of c-linolenic acid in the lipids of chicken breasts produced [47]. On the contrary, Oliveira et al. [48] emphasize the significance of c-linolenic acid as a representative of n − 6 PUFAs, which has a synergistic effect with n − 3 PUFAs such as DHA and EPA, whereas dihomo-c-linolenic acid and arachidonic acid possibly had a higher concentration due to a higher fraction of c-linolenic acid. However, Khatibjoo et al. [49] report that a high concentration of linoleic acid in the meat of broilers fed linoleic acid could reduce the proportion of monounsaturated fatty acids and increase the proportion of polyunsaturated fatty acids. Another study by El-Zenary et al. [50] revealed that the overall n − 6 PUFA content of boneless, skinless breasts mirrored that of linoleic acid in the diet. Total n − 6 PUFAs were highest in birds, primarily due to a higher conversion of linoleic acid to arachidonic acid. Te n − 6 PUFAs or their sources, such as fsh oil, palm oil, soybean oil, and linseed oil, also promote bone formation, development, and growth by enhancing mineral metabolism, particularly that of calcium, zinc, and magnesium, which renders them inaccessible after age [20]. 

Te data revealed that the arachidonic acid content of Hinai jidori fish can be increased with arachidonic acid dietary supplements and that Hinai jidori meat and soup with a higher arachidonic acid content had a significantly better taste perception than those with a low arachidonic acid content [6]. Arachidonic acid stimulates the TRPM5 cation channel, a component of type II receptor cells’ sweet, umami, and bitter taste pathways, as suggested by Liu et al. [51]. Takahashi et al. [6] have demonstrated that the concentration of arachidonic acid in chicken fesh may be altered through dietary supplementation with arachidonic acid (AA) and genetic selection utilizing the polymorphism of the FADS1 and FADS2 genes as selection markers. These techniques enhance the favor of the chicken.

In addition, it was determined that the inclusion of 2% of various sources of omega-6 fatty acids (particularly flax seed oil) in the diets of broiler breeders might reduce late embryonic mortality, hence enhancing fertility, hatchability, sperm quality, and sperm quantity [20, 52]. In addition, n − 6 FA-rich diets had a beneficial impact on semen volume and total spermatozoa count but a detrimental impact on spermatozoa concentration. Furthermore, avian sperm often contains a high proportion of PUFA, especially n − 6 PUFA [49]. Table 2 displays the effects of various plant feed resources with the highest omega-6 content on the performance of broilers. Generally, omega-6 supplementation improves broiler performance by increasing body weight and internal organs, increasing the number of fatty acids in meat, influencing mineral metabolism, and enhancing reproductive performance.

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