The enhancement of NZnO whatever the concentration in G4, G5, and G6 on the final BW and cumulative BWG in comparison to inorganic zinc source-supplemented groups. In addition, there was an enhancement in FCR and FE was reported in NZnO-supplemented groups (G5 and G6) at the levels of 10 and 5 mg/kg diet, respectively. This enhancement could be attributed to the unique features of zinc in nanoform. Generally, zinc is a vital nutrient that plays a wide range of roles in the metabolism of proteins, carbs, and fats, as well as in the synthesis and release of hormones, including growth hormone., insulin, and sex hormone; hence, it may have an impact on the productivity and reproductive abilities of animals. Also, zinc is a compound of DNA-binding proteins that controls the expression of genes and contributes to the synthesis of proteins and nucleic acids. (McDowell 2003). Moreover, Hafez et al. (2017) conveyed that the improvement in growth could be ascribed to the function of NZnO in augmenting the intestinal absorptive capacity by enhancing the length and depth of the crypt's mucosal and villi. All these features augment the role of nano zinc oxide and lead to improved body health and, consequently, the growth parameters of broilers. The same trend was declared by Zhao et al. (2014); they found that, in comparison to 60 mg/kg ZnO, nano zinc oxide at levels of 20 and 60 mg/kg diet could boost BW, WG, and feed efficiency. It was observed that nano zinc (20 mg/kg) significantly enhanced the FCR, WG, and ADG (Average daily gain) of broilers (Mohammadi et al. 2015). Furthermore, Joshua et al. (2016) verified that the use of nanoelements (zinc, copper, and selenium) can improve the post-hatch performance of broiler chickens, including body weight, weight gain, and feed conversion, and that these elements are safe for the embryo. Mahmoud et al. (2020) showed that 10 ppm NZnO considerably increased the feed conversion and body weight gain increase compared to the control (0 ppm).
Our findings were contradicted by, Rossi et al. (2007) who found no variation in ADG between broilers fed 0 and 15– 60 mg Zn/kg feed. Ramiah et al. (2019) showed that the broilers' body weight was unaffected by NZnO supplementation at doses of 40, 60, and 100 mg Zn/kg feed. Bami et al. (2020) found that broiler growth features were unaffected by using nano Zn sources (25 and 50 ppm). The average values of crude protein, calorie conversion ratio, body weight growth, and final body weight did not differ statistically significantly between treatment groups that received 100, 80, 60, 40, and 20 mg NZnO/kg of feed (El-Haliem et al. 2020). Asheer et al. (2018) observed that substituting nano zinc oxide at levels of 25, 50, 75, and 100% for traditional zinc in a broiler feed did not significantly affect the broiler's weekly FCR. Eskandani et al. (2021) claimed that the ADG, ADFI, and FCR of broilers in the starting phase were not significantly affected by 30, 50, 70, and 90 ppm of nano Zn oxide addition. Variations in feed intake, bird strain, sources and quantities of zinc, and the length of the experiment could all be contributing factors to the discrepancy (Alian et al. 2023).
There was an improvement in the BW and WG of broilers because of organic zinc methionine supplementation (100 mg Zn/kg diet) compared to conventional inorganic zinc sources. This is due to the inorganic zinc in the intestine linked to phytic acid. However, the lack of free divalent cations required for intestinal chelation prevented organic zinc sources from combining with phytates, resulting in increased absorption and utilization (McDowell 2003). This is parallel to several reports that state that organic zinc has a higher bioavailability and will have a greater impact on broiler performance (Salim et al. 2012). The data matched those of El-Husseiny et al. (2012) who found that BWG was enhanced by feeding broilers' diets with 50% organic forms of zinc and magnesium (Mn), and copper (Cu) of their requirements. Liu et al. (2013) claimed that when compared to Zn sulfate, chicks fed with Zn proteinate (10, 20, 40, or 80 ppm) displayed higher WG. Moreover, Olukosi et al. (2018) revealed that broiler performance was improved more by organic zinc and copper than by sulfate zinc and copper. The group that received a 50 mg/kg diet had a significantly higher body weight, indicating the effectiveness of organic zinc (Chand et al. 2020).
On the other hand, it was discovered that feeding broilers with organic zinc source at doses of 15, 30, 45, or 60 ppm did not impact their BWG (Rossi et al. 2007). Bun et al. (2011) discovered that the growth traits was unaffected by Zn methionine hydroxyl at 0, 20, 40, and 60 mg/kg diet. Furthermore, Sunder et al. (2013) demonstrated that taking supplements containing organic zinc and magnesium had no influence on weight increase or body weight. Kakhki et al. (2017) noted that broiler hens fed diets enhanced with 60 or 120 mg Zn/kg of zinc methionine (Zn-Met) did not exhibit any variations in ADG. The lack of effect in terms of performance of birds might result from using different types and dosages of zinc in the feeds of broiler chickens.
Our findings showed that the cumulative FI did not differ statistically between the zinc-supplemented groups. This is a match with that mentioned by Sunder et al. (2013) who revealed that 40, 80, and 160 ppm of organic zinc did not influence the FI of broiler chicks. Moreover, broiler chicks received diets enriched with Zn 60 or 120 mg/kg, as Zn-Me did not exhibit any variations in ADFI (Kakhki et al. 2017). Finally, dietary nano Zn treatments (30, 50, 70, and 90 ppm) had no significant impact on ADFI in the starter phase compared to ZnSO4 and Zn amino acid complexes (70 ppm) (Eskandani et al. 2021). However, Jahanian et al. (2008) stated that the average feed intake was decreased (P < 0.001) when the Zn level was increased from 80 to 120 mg/kg diet. The lack of significant impact on feed intake in the groups receiving NZnO suggests that the zinc levels in the control diet were adequate for the growth of the birds. Although the NRC (NRC 1994) recommended that broiler chicks require 40 mg/kg of zinc.
Nano zinc oxide (G4, G5, and G6) and organic zinc methionine group (G3) significantly achieved the highest performance index compared to zinc oxide (G1), which was greatly matched to the improved BW and FCR. FCR is one of the primary indicators used to evaluate the productivity and profitability of the broiler sector. The lower FCR in Zn-supplied groups, either in nano or organic zinc form, indicates that zinc was well utilized by the broilers, increasing the performance index. Also, the augmented feed utilization in broilers given Zn-enriched diets may be because Zn can boost the intestine absorption capacity (De Grande et al. 2020), leading to an increase in the brush border enzyme activity and nutrient transport systems (Awad et al. 2017). Additionally, the role zinc plays in DNA synthesis and feed utilization may explain why broilers fed diets supplemented with zinc had increased ADG (Li et al. 2019). Moreover, it is possible to corroborate the finding that feeding nano zinc oxide at a level of 5 mg Zn/kg caused a significant increase in EEI, as EEI and FCR are inversely dependent on the equation used. This finding agrees with El-Husseiny et al. (2012) who mentioned that broilers given a diet provided with organic 50% Zn, Mn, and Cu had a significantly adjusted (P ≤ 0.001) FCR. El-Katcha et al. (2017) revealed that NZnO addition at 60, 45, or 30 mg/kg diet enhanced the BW, FCR, and PI of broilers. This is also in accordance with Akhavan-Salamat and Ghasemi (2019), and El-Haliem et al. (2020) who stated that the FCR significantly improved at the level of a 40 mg/kg diet of nano zinc oxide. The highest European production efficiency index (EPEI) was observed in 70 and 90 mg NZnO-supplemented groups (Eskandani et al. 2021).
Furthermore, NZnO at a level of 5 mg Zn/kg (G6) significantly improved the protein efficiency ratio (PER) for finisher diets. These results also agreed with Abdel-Wareth et al. (2022), who noted that the digestibility of crude protein, crude fat, and crude fiber in the broiler was linearly increased by nano zinc oxide (20, 40, and 60 ppm) relative to the control. Among the zinc source-supplemented groups, better growth performance parameters were observed in nano zinc oxide groups, especially G5, which suggested that these groups' birds utilized nano ZnO more effectively. This indicates that nano ZnO was a better source for enhancing the efficacy of nutrient utilization.
The other performance parameters of the broiler, such as livability and mortality, were not markedly impacted by the zinc addition in the diet. This was in line with previously stated reports that the livability or mortality did not significantly change when zinc supplementation was used (Zakaria et al. 2017). No differences in mortality rates were detected in broilers given diets enriched with 60 or 120 ppm of Zn-methionine (Kakhki et al. 2017). As well, the broiler mortality rate was not significantly affected by NZnO at a rate of 0, 40, 60, and 100 mg/kg diet (Ramiah et al. 2019). There was no difference noticed in the livability of chicks received organic or inorganic Zn at the dose of 50 and 60 ppm (Chand et al. 2020).
Using nano zinc oxide, whatever the concentration, and zinc methionine significantly gave the highest selling price and net revenue. Besides, the adding of nano zinc oxide in G5 and G6 at the levels of 10 and 5 mg Zn/kg diet, respectively, significantly enhanced economic efficiency compared to chicks in G1 and G2, as well as numerically to chicks in G3 and G4. This improvement was matched with the enhancement in feed conversion and weight gain of broiler chicks. This data agreed with results informed by El-Husseiny et al. (2012) who noted that chicks fed a diet with 50 or 100% of the organic Zn, Mn, or Cu required by broilers had a greater relative economic efficiency. Additionally, poultry growth performance and economic benefits were enhanced by nano zinc oxide (Swain et al. 2016). It was claimed that the optimal level of feed additives for broiler chicks to have the optimum growth and economic efficiency be 20 mg/kg of nano ZnO (Zhao et al. 2014). When compared to ZnO, the addition of nano zinc oxide (40 mg Zn/kg diet) resulted in the best return, selling price and cost savings (Alian et al. 2022). One other thing is that the net profit is unaffected by substituting nano Zn for traditional zinc source at levels of 0.0, 25, 50, 75, and 100%. (Asheer et al. 2018).
Blood parameters are employed in poultry and livestock as an indicator of their physiological, pathological, and nutritional status (Ogbuewu et al. 2017). Nano zinc oxide in G6, followed by G5, and G4, significantly achieved the highest SOD activity compared to others. It was also reported that G4, G5, and G6 significantly achieved the lowest levels of serum MDA compared to G1 and G2. And zinc methionine has a significant improvement in SOD activity. Various stresses are associated with poultry farming, which lowers the productivity of chickens. Studies have shown oxidative stress to be the primary cause of this stress at the cellular level (Surai 2016). Zn deficiency is associated with oxidative stress in poultry, which can be alleviated by vitamin E addition (Kraus et al. 1997). Because zinc contributes to the synthesis of antioxidant enzymes, it has been proposed that zinc has antioxidant benefits in chickens (Saleh et al. 2018) and it elevates antioxidant vitamin levels in the blood (Onderci et al. 2003). Zinc also promotes the production of SOD, an antioxidant enzyme that protects cells from the destructive effects of free radicals by converting superoxide anions to hydrogen peroxide (Niles et al. 2008). Besides, research has revealed that zinc increases the synthesis of metallothionein, a cysteine-rich protein that scavenges free radicals (Maret 2000). On the other side, MDA is a consequence of lipid oxidation (LP). Zinc has a crucial role in reduction of the lipid oxidation in the body (Zago and Oteiza 2001). Similarly, some investigators, i.e., Marreiro et al. (2017) mentioned that zinc decreases MDA, indicating the crucial function that zinc plays in reducing lipid peroxidation in the cell membrane. A recent study by Abdel-Monem et al. (2021) and Dukare et al. (2021) showed that 80 ppm of ZnO-NPs significantly increased the amount of SOD and total antioxidant capacity in chickens and decreased the amount of lipid peroxidation. Besides, Hafez et al. (2020) revealed that ZnO-NPs decreased the MDA value and increased (P < 0.05) the activity of SOD and catalase. Additionally, adding Zn-Met and ZnO-NPs to broiler chickens' diets at a rate of 40 mg/kg may enhance their antioxidant capacity when exposed to high ambient temperatures (Akhavan-Salamat and Ghasemi 2019). In the same trend, De Grande et al. (2020) found that zinc amino acid (ZnAA) at 60 mg/kg was shown to have higher glutathione peroxidase levels and lower serum MDA levels in broilers compared to Zn sulfate. In contrast, Fathi (2016) found that the addition of 40 mg/kg of micro ZnO did not significantly influence the SOD activity in chickens. El-Katcha et al. (2017) claimed that the addition of nano zinc (60, 45, 30, or 15 ppm) numerically lowered the blood MDA level in chicks compared to inorganic zinc, while zinc polysaccharide complex (30 or 15 ppm) had no influence on the level of serum MDA. The detected disagreement might be due to differences in health conditions and might be because later research used high concentrations of NZnO. These results showed that zinc could boost antioxidant status and inhibit LPO (lipid peroxidation) in broilers. The more noticeable effect was achieved by nano zinc oxide in G6, followed by G5 and G4.
No significant variation was observed in the cholesterol and triglyceride levels among the different experimental groups. Also, the nano zinc oxide – supplemented group gave the highest HDL level. There was no statistical difference between G6 (nano zinc oxide) in the level of LDL compared with G5, G4, and G3. Our results corroborate the data that confirm the prominent role of zinc on lipid metabolism. Al-Bayti et al. (2022) verified that zinc has a protective effect on lipid metabolism markers in laboratory rats. Furthermore, studies have shown a correlation between zinc deficiency diets and lower plasma values of triglycerides, LDL, HDL, and total cholesterol. This may result from a reduction in the consumption of fat and calories as well as a decrease in the absorption of dietary lipids (Wu et al. 2004) and it could be as a result of the fact that zinc is a crucial part of many metalloenzymes needed for lipid absorption and digestion. (Al-Daraji and Amen 2011). Like our data, it was conveyed that Zn sources had no impact on the serum cholesterol values in chicks (Lü and Combs Jr 1988). Malcolm-Callis et al. (2000) notified that serum cholesterol was not affected by zinc feeding at a rate of 20, 100, and 200 mg zinc/kg. Also, Kucuk et al. (2008) found that 30 ppm zinc supplementation has no impact on the total cholesterol and triglyceride values. Moreover, using nano zinc treatments at doses of 10, 20, and 40 mg/kg diet, triglycerides were not significantly (P > 0.05) altered (Fathi et al. 2016). Besides, the present data came in harmony with the results of Aksu and Ozsoy (2010) who reported that organic complexes of zinc, copper, and manganese increased HDL in the blood plasma of chickens. The higher HDL is most likely the result of an increase in fat and calorie consumption following zinc feeding. It was also shown that there was a rise (P < 0.05) in HDL levels in birds receiving 60 or 90 mg of NZnO/kg feed (Ahmadi et al. 2013). Nonetheless, plasma cholesterol levels were affected by ZnO given at a rate of 80 mg/day, either on its own or in combining with vitamins or copper (Gensler et al. 2002). Herzig et al. (2009) shown that the plasma cholesterol of broilers reduced when given a diet rich in zinc. Parák and Straková (2011) showed this impact when breeding cocks were fed inorganic versus organic zinc. Ahmadi et al. (2013) showed a decrease in triglycerides, total cholesterol, and LDL (P > 0.05) values in chicks who were given a diet with 60 or 90 mg of NZnO. It was reported that female broilers had a significantly lower cholesterol level than males, suggesting that sex is a major factor affecting the plasma cholesterol level of broiler chickens (Salim et al. 2012). Also, the inconsistent findings in these studies might be due to the period of sample collection within the day, as blood indices vary with the time of the day.
The total protein, A/G ratio, and albumin level were significantly higher in the nano zinc supplemented groups (G4, G5, and G6). The globulin level did not vary among the experimental groups. Serum proteins are useful indicators of the condition of bodily cells, tissues, and organs, as well as the metabolism of feed that has been consumed (Fuhrman et al. 2004). Walker et al. (1990) said that various factors, including the protein level, might be considered when evaluating overall health. The improvement in total serum protein because of nano zinc oxide supplementation could be illuminated by the pivotal role of zinc in nutrient utilization and protein metabolism. Zinc as previously stated, is a necessary part of the enzymes that synthesize proteins and nucleic acids (Maggini et al. 2007). These data were proven by Feng et al. (2010), who discovered that feeding chickens 90 and 140 mg/kg of organic zinc greatly increased the birds' total serum protein. Additionally, feeding Zn supplements to breeder broiler chicks raises their total serum protein levels (Al-Daraji and Amen 2011). In contrast, it was shown that the amount or type of zinc did not affect blood total protein or albumin (Sarvari et al. 2015). Nano zinc-supplemented groups (G4, G5, and G6) significantly reduced AST and ALT levels and serum creatinine. The dietary zinc sources didn’t reveal significant changes in ALP, LDH, or serum uric acid levels. The collected data is in agreement with Ahmadi et al. (2014) who mentioned that dietary NZnO (30, 60, 90, or 120 mg/kg diet) significantly (P < 0.05) decreased blood AST and ALT values compared to basal diet. When broilers were fed 0, 10, 20, and 40 mg/kg of nano zinc oxide, there was no significant change in the activity of alkaline phosphatase (ALP) (Fathi et al. 2016). El-Katcha et al. (2017) demonstrated that nano zinc (60, 45, 30, or 15 ppm), decreased blood creatinine while having no significant effect on serum uric acid concentration. Abdel-Monem et al. (2021) illustrated that dietary zinc oxide did not significantly influence serum ALP and uric acid, either added in bulk or nanoform (40 and 80 ppm). Also, nano zinc oxide (0, 20, 40, or 60 mg/kg) exhibited lower serum ALT, AST, and creatinine in broilers (Abdel-Wareth et al. 2022). Conversely, Fathi et al. (2016) stated that serum concentrations of ALP level were significantly elevated at 20 mg/kg nano-ZnO. It was demonstrated that serum AST concentrations were not significantly affected by nano zinc (60, 45, 30 or 15 ppm) and there was a numerical increase in serum ALT and ALP levels in broilers (El-Katcha et al. 2017). In ovo injection and Zn addition (i.e., 0, 60, 0, and 0 mg Zn/egg, 0, 0, 100, and 200 mg Zn/kg basal diets, respectively), revealed no statistical difference in AST and ALT in the blood among the four treatments (Kim and Kang 2022). The dietary supplementation of ZnO-NPs at a dose of 40–160 ppm has no alteration in the serum values of AST and ALT (Zhang et al. 2022). The data indicated that the addition of NZnO caused no obvious negative effects on liver and kidney health condition, as manifested by unaffected serum activity levels of some enzymes (ALP and LDH) and concentrations of uric acid. Besides, NZnO lessens blood serum ALT, AST, and creatinine levels.