Animal wellbeing may be achieved by enhanced antioxidant capacity (Li et al. 2018). CAT, SOD, and GSH-Px, and lactoferrin, carotene, vitamin C, glutathione (GSH) as non-enzymatic constituents, are antioxidant enzymes metabolites in physiological antioxidant systems (Eşrefoǧlu 2009). The main selenium-dependent enzymes are; glutathione peroxidases (GSH-Px) which catalyze H2O2 and ROS to water (Behne and Kyriakopoulos 2001), superoxide dismutase (SOD) catalyzes superoxide anion to H2O2 and molecular O2 (Okado-Matsumoto and Fridovich 2001), and catalase (CAT) catalyze hydrogen peroxide decomposition to yield water and oxygen, thus, protecting cells from oxidative damage (Nandi et al. 2019). Hence, dietary Se supplementation enhanced antioxidant capacity in animals (Surai and Dvorska 2002).
In general, the efficacy of organic Se over bioavailability and tissue retention is superior to that of inorganic Se. Minerals' utilization is dependent on their bioaccumulation and retention (Li et al. 2018). Similarly, compared to inorganic, dietary organic, and Nano-Se supplementation could improve the concentration of breast muscles, liver, and serum Se (Mohapatra et al. 2014; Mohamed et al. 2020), possibly resulting in greater activity of GSH-Px. Additive supplementation (e.g. Se) improves the activity of antioxidant enzymes in chickens through antioxidant capacity (Mohapatra et al. 2014; Markovic et al. 2018).
In the present study, organic Se bacteria (ADS18) and yeast (Se-yeast) have demonstrated stronger antioxidant activity in laying hens serum and liver compared to inorganic (sodium selenite) Se and non-supplemented hens, in line with previous findings. The serum TAC value was significantly higher in the nano selenium or Se-yeast groups than in the control group, and Se-yeast supplementation also enhanced serum CAT and SOD activity in Brown Hy-line hens (Meng et al. 2020). Moreover, compared to positive control groups of local Chinese yellow male chickens infected with Eimeria tenella, (Mengistu et al. 2020) reported higher serum SOD and GSH-Px1 activities with Se-enriched probiotics. Xia et al. (2020) observed a linear and quadratic increase in liver GSH-Px1 and SOD activity in breeder ducks with increased dietary Se levels. In T-2 toxin (T-2) or HT-2 toxin (HT-2)-induced cytotoxicity and oxidative stress broiler hepatocytes, Yang et al. (2019) observed a significant increase in hepatic GSH-Px, SOD, and CAT activity that was activated by toxins with 1 µM DL-Selenomethionine. Also, relative to those laying hens fed with the basal diet, Meng et al. (2019) reported an improvement in serum GSH-Px, T-AOC, and CAT activities in the nano-Se or sodium selenite group. Dalia et al. (2017) found the highest serum GSH-Px activity and CAT liver with bacterial organic Se supplementation of ADS18, respectively. Li et al. (2017) reported increased serum and breast GSH-Px activity with Se-yeast, Met-Se, and Nano-Se dietary supplementation compared with the SS group. Selenium is an indispensable constituent of the GSH-Px enzyme, actively involved in oxidative damage defense (Rotruck et al., 1973; Fernández-Lázaro et al., 2020).
In this study, the enzyme's activity was significantly enhanced by Se supplementation (organic) in serum and liver. The response of external stimuli and free radicals' metabolism capacity in organisms can be assayed by T-AOC (Huma et al., 2019). The body's total antioxidant capacity can be measured through TAC values (Zhang et al. 2011), with low or higher T-AOC suggesting oxidative stress or susceptibility to oxidative damage, respectively (Meng et al. 2020). Consequently, dietary supplementation with organic Se of ADS18 bacteria or Se-yeast could promote the antioxidant capacity of laying hens, thereby ensuring that egg-laying efficiency is preserved. The potential reason was that ADS18 or Se-yeast contains organic Se, which is much less harmful and more bioavailable and effectively preserved in the tissues of the body.
Furthermore, hens supplemented with Se (regardless of Se form) improves all the measured antioxidant indexes except SOD which was not affected by dietary Se treatments in the liver. In summary, with the addition of bacterial organic Se, the serum and liver TAC, GSH-Px, CAT, and SOD activities produced by the cells to prevent the occurrence of oxidative damage (Xu et al. 2016; Yang et al. 2019), were further enhanced, indicating that the bacterial organic Se of ADS18 could partially reduce oxidative damage by regulating the activities of enzymes (antioxidases). Although catalase and superoxide dismutase are not Se-dependent enzymes for their functions, the presence of Se in animal rations can influence their activities via thyroid hormone metabolism (Meng et al. 2020; Mohamed et al. 2020).
Markers of nutritional conditions in growing animals may be serum biochemical parameters (Mu et al. 2019). The maintenance of plasma osmotic pressure, provision of energy, repairing the worn-out tissue, carrier, and transporter of nutrients to sustain body tissue protein, active balance of cells is the role of albumin protein, which is synthesized in the liver (Surai 2002). Liu et al. (2020a) found no major variations in albumin, total protein, or blood urea nitrogen after adding 0.3 and 0.5 mg/kg addition of sodium selenite and selenium yeast, respectively. Similarly, Hossein Zadeh et al. (2018) did not note any effect on the blood constituents of either organic or inorganic forms of Se.
Different Se sources supplementation did not affect blood albumin, total protein, globulin, or the albumin globulin ratio in this study. Besides, as kidney function makers, gamma-glutamyl transpeptidase, total bilirubin, creatinine, and urea have not been affected and are per the previous reports (Kumar et al. 2008; Alimohamady et al. 2013; Sethy et al. 2015). Se has a greater impact on serum biochemical parameters, with a significant impact on lipid metabolism and a lesser impact on liver functions. The decreased total cholesterol, triglycerides, and VLDL observed as a result of supplementation with Se-yeast or ADS18 showed that the organic form of Se could play an anabolic role in fat deposition than the inorganic source of Se (Jeyanthi 2010; Sheoran 2017). Besides, the composition of fatty acids in the whole body could be modulated by supplementation Se via organic forms in yeast or bacteria. In a research study conducted by Dhingra and Bansal (2006) and Yang et al. (2010), they reported dietary Se supplementation plays a role in increasing the activity of LDL receptor, but, reduces the expression of 3-hydroxy 3-methylgluatryl coenzyme A (HMG-CoA) reductase in rat and also invariably decrease serum LDL and cholesterol.
The results of this research were inconsistent with the study by Abdel-Azeem et al. (2019) and Amer et al. (2018), which showed the hypolipidemic effect of organic selenium (Se-yeast) in wean male rabbits by significantly reducing serum total cholesterol and LDL-cholesterol. In an in vitro study with Wistar rats, Urbankova et al. (2021) reported that Se deficiency tends to result in increased total cholesterol, LDL, and a significant decrease in HDL concentrations. Antioxidants’ hypocholesterolemic activity may be due to oxysterols’ inhibition of sterol biosynthesis (Revilla et al. 2009; Hozzein et al. 2020). Consequently, the antioxidant effect is principally attributed to selenoenzymes, glutathione peroxidase (GPX’s), and thioredoxin reductase. In studies with growing pullets, Jegede et al. (2012) showed that, compared to CuSO4, supplementary trace (Cu-P) minerals reduced plasma cholesterol, LDL, and triglycerides. Kim et al. (1992) showed that the mechanism of Cu is to control cholesterol biosynthesis by reducing hepatic glutathione concentration and changes the hepatic GSH: GSSG (oxidized glutathione) ratio, thereby, increased the activity of 3-hydroxyl-3-methylglutaryl Co-(HMG-CoA) reductase. Glutathione plays an important role in regulating cholesterol biosynthesis via HMG-CoA reductase stimulation (Konjufca et al. 1997), which is the primary enzyme of cholesterol biosynthesis, and in turn, decreases plasma cholesterol concentration. The above-mentioned pathway can explain the reduction in plasma cholesterol by supplementing the organic form of Se.
Organic Se supplementation (Se-yeast or ADS18) has demonstrated a significant decrease in triglyceride concentration relative to inorganic and non-supplemented hens in the present study. These findings were consistent with the results of Jegede et al. (2012), who reported a significant decrease in triglyceride concentration in growing pullets supplemented with Cu-P compared to CuSO4. Moreover, dietary Se appears to have a major effect on aspartate aminotransferase (AST), alkaline phosphatase (ALP), but no effect on alanine aminotransferase (ALT) in the present study. Sizova et al. (2021) observed a substantial increase in ALT activity in broilers fed organic zinc on days 35 and 42, compared to control, though AST did not change significantly. Broiler chickens fed 0.3 ppm organic Se (Perić et al. 2009), 0.5 and 1.0 mg Se per Kg had significantly lower ALT and AST enzyme activity (Biswas et al., 2011).
In contrast, none of the blood constituents ALT, AST, TP, albumin, urea, and creatinine are affected by either inorganic (0.5 and 0.15 mg Se) or organic (0.35 mg Se) (Okunlola et al. 2015). Blood enzymes (ALT, AST, ALP, LDH) cause oxidative damage to the liver and kidneys, which can be reduced, imparted, and enhanced through redox status to protect against oxidative damage (Zhang et al. 2018).
The concentration of Se in egg yolk, breast muscle, and serum increased after dietary Se supplementation with Se, according to this study. Avian eggs are ideal vectors used to study the absorption and retention of microminerals, including Se at varying dosages and forms (Pan et al. 2007; Delezie et al. 2014). Dietary supplementation with Se increased egg yolk Se in the current study, which is consistent with previous studies (Liu et al. 2020b; Zhang et al. 2020). Lu et al. (2020) found higher Se concentrations in eggs and breast tissue of laying hens fed 0.1 to 0.4 mg/kg of Se from Se-enriched yeast than in eggs and breast tissue of hens fed SS or basal diet. Also, Liu et al. (2020a) found that 0.5 mg/kg of Se-yeast resulted in higher Se deposition in egg yolk than did sodium selenite in laying hens. According to Zhang et al. (2020), adding Se-yeast to the diets of laying hens helps to increase Se deposition in eggs. Likewise, hens fed with hydroxy selenomethionine and Se-yeast had higher concentration yolk Se than when fed the SS and basal diets (Moslehi et al. 2019).
Dietary Se supplementation with Vitamin E, Se, and their blend significantly increased the concentration of Se in breast tissue and certain laying hens’ organs (Çelebi 2019). Similar results were found in eggs and breast meat Se concentration in laying hens (Lu et al. 2019; Lv et al. 2019), serum, liver, and muscle Se in growing lambs fed different concentrations (0.2 to 1.4 mg/kg DM) and Se sources (Se-met or Se-yeast and SS) (Paiva et al. 2019). Hens fed organic Se showed higher egg Se content compared to inorganic Se in response to the effectiveness of organic Se over inorganic form (Skřivan et al. 2006; Chantiratikul et al. 2008).
The difference in Se deposition in egg yolk between inorganic and organic Se sources may be due to their dissimilar metabolizable pathways, as SS cannot be completely metabolized to SeMet in poultry, which could explain the current findings (Sunde et al. 2016). Sodium selenite has a lower absorption rate and a higher excretion than organic Se (Mahan and Parrett 1996). Organic Se is actively absorbed and is dependent on the metabolization and integration of mainly organic selenomethionine with methionine into egg proteins and tissues (Čobanová et al. 2011; Surai and Kochish 2019). Selenoproteins from the liver are incorporated as part of egg yolk synthesis, whereas the uterine tubes incorporate selenomethionine as a part of egg white synthesis (Mahan and Kim 1996; Lv et al. 2019). The higher Se deposition in hens’ eggs fed Se-yeast might perhaps be connected to the upregulation of methionine (Met) metabolism gene glycine N-methyltransferase (GNMT) in the liver (Meng et al. 2019). With different Se levels and time, there is a positive increase in egg Se concentration (Lu et al. 2019).
As hypothesized, with dietary Se supplementation, the concentration of Se in breast tissue and serum of laying hens was increased, and organic Se (ADS18 or Se-yeast) was more efficient compared to inorganic Se. Paiva et al. (2019) relate serum Se concentration to time and dose-dependent regardless of Se form. Application of 0.30 mg/kg selenomethionine in broiler breeder diets results in higher serum and tissue Se deposition than other sources of Se (Li et al. 2018). Also, Han et al. (2017) reported a higher Se concentration from different Se sources in serum and organs of layers fed 0.3 mg/kg Se. Moreover, layer chicks fed a 0.3 mg/kg diet of both nano-Se and sodium selenite showed a significant increase in Se concentrations in tissues, organs, and serum (Mohapatra et al., 2014). Because SeMet is available in an organic form of Se and is closely linked to its bioavailability and assimilation (Briens et al. 2013; Mohapatra et al., 2014), the present findings are justified.
The significant differences found between the treatment groups in serum and breast tissue may be due to dissimilar metabolic pathways, as Se can be incorporated into selenoprotein as selenocysteine from inorganic and organic sources, while SeMet is incorporated in a nonspecific direction as methionine (Surai and Kochish 2019). Inorganic Se compounds are mainly used to synthesize selenoproteins and not replenish Se deposits in tissues in the Se metabolism pathway (Moslehi et al. 2019). The addition of organic Se (Se-yeast or SeMet) into the diet is connected with a significant increase of Se level in laying hens tissue (Invernizzi et al. 2013; Jing et al. 2015). Therefore, the quantity of Se uptake and its absorption in egg, tissue, and blood of laying hens is determined by the Se chemical form in organic sources (Jing et al. 2015). However, more research is required to explore the complete metabolic pathway of organic (Se-yeast or ADS18) sources.