The role of the micronutrients zinc in animal health is well documented . This nutrient cannot be stored in the body ,therefore, regular dietary intake of Zn is required to meet the physiological needs and functionality requirements [25,40].
The findings of the present study confirm that supplementing basal diet with ZONPsto broiler chicksresulted ina significant increase in body weight, increased feed consumption and improved feed conversion ratio compared with control chicks. In this respect, present results are in close agreement with those reported by  revealed that supplementation of Nano Zno into broiler diet at 2.5 ppm recorded significantly higher body weight gain, feed intake, and better feed conversion ratio. Also, found a significant improvement in body weight, weight gain, feed intake, and feed conversion ratio in birds fed diets supplemented with 0.2 or 0.3 g/kg of ZONPs. Similarly, present results are in a harmony with  investigate the effect of different levels (20, 40, 60, 80 and 100 mg /kg feed) of dietary Nano zinc oxide supplementation on growth performance, and economic efficiency of cobb broiler chicks for 6 week of age and found that birds fed 40 mg ZONPs recorded the highest LBW, TBWG and the best FCR value compared with the other treatments. Besides, the same group (40 mg ZONPs / kg diet) significantly improved performance index value ( PI value).Furthermore,  reported that broiler chicks fed with ZONPs at 90 mg / kg for 35 days of age, showed an improvement in body weight compared with the bulk zinc oxide-administered group at 3000 mg /kg diet. Moreover,  evaluate the growth performance and economic benefits of nano-zinc compared to inorganic and organic sources of zinc supplementation in Giriraja; dual purpose chickenand concluded that growth performance (body weight, FC and FCR) and production economics were better during all weeks in chicken fed ZONPs supplementation at 60 mg/kg as compared with chicks fed a supplemented diets with Zinc sulphate and Zinc methionine at (30 and 60 ppm) respectively.
In addition, several previous results in the literature confirmed thatZnO nanoparticles at 20 to 60 mg/kg of diet could be appropriate levels and a considerable source of Zn to enhance BWG and achieve a better FCR of broiler chickens [46-54] and this was matched with the present work and that 40 mg/kg Nano-ZnO is the optimal level in diets.
The performance improvement may be attributed to the role of ZONPs in increasing the intestinal absorptive capacity as it increases mucosal length, villi length and width, and crypt depth , in addition to the higher absorption efficiencies of Zn nanoparticles due to its unique physical characteristics of transport and uptake, resulting in improved Zn bioavailability [13,55].
The positive effect of ZONPs supplementation on growth performance through the current study are corroborated with earlier works reported and may be due the important role of Zn in the overall performance and physiological process of poultry, as it is the integral component of more than 300 enzyme systems known as metalloenzymes, which are involved in metabolism of energy, nucleic acids, lipid and protein [4,56-58]. Furthermore, zinc is a known essential microelement for the growth performance of broilers so that, its deficiency in animals is characterized by appetite reduction, decreased FI, circulating levels of growth hormone (GH), and decreased hepatic production of Insulin growth factor (IGF-I) and growth falling in broilers [8,49; 59-61].
It is also, suggested that, zinc oxide in broiler can increase the concentration of sucrase in small intestine and result in increased carbohydrate absorption . Zinc, in the composition of nanoparticles, has antioxidant and anti-stress properties, affects the intestinal microbiome of broiler chickens [63,64].
Carcass and relative organ weights.
The finding in the present results showed that supplementation of broiler diets with ZONPs at 40 or 60 mg / kg affect the carcass weight and internal organ weights as a percentage of live body weight. increasing carcass and liver weight and decreasing kidney, proventriculus, gizzard and intestine weight was observed as compared with control.
These results can be corroborated with earlier work reported byas the relative weight of proventriculus at 40 and 100 mg ZONPs /kg of diet were significantly lower and the relative weight of the intestine was decreased by lowering the ZONPs levels with significant differences at 40 and 20 mg/kg of diet compared with the control. Moreover,weight of small intestine was lower and the liver weight was significantly increased as percentage of LBW in birds fed diet supplementation with 60 or 90 mg ZONPs / kg than other treatments. An explanation for increasing liver weight may be due to positive effect of ZONPs on better digestion and absorption of nutrient in gastrointestinal tract and or probably to be higher bioavailability zinc in the form of nanoparticles. As well as, the mention reason caused that zinc retention was higher in liver of broiler after absorption and inters to portal of blood.
current results was also consistent with those reported by asrelative weight of gizzard was significantly reduced and no significant effect on the relative weight of heart with ZONPs (10 and 30 ppm) and the edible yield values in 20 and 40 ppm of ZONPs group were significantly higher than that in control groups.
A non-significant reduction in relative weight of gizzard of broilers fed diet containing 100 or 200 ppm ZONPs was reported by .In another study suggested that dietary ZONPs at 80 mg/kg had significantly improved carcass yield and increased the relative weight of the digestive organs of broilers.,In addition, present study also clarified that addition of ZONPs to broilers’ diet significantly increased the eviscerated and edible yield compared with control groups. This finding was consistent with the previous investigations reported that dietary ZONPs significantly increased dressing percentage, carcass yield, and carcass weight at concentrations from 40 to 90 ppm [29, 53, 66].
Blood biochemistry parameters
Blood biochemistry parameters are important markers of physiological status in the body. The blood parameters of the treated groups varied significantly in terms of Chol, HDL, TG, LDL, ALT, AST, uric acid and serum creatinine concentration. Present results are congruentwith work reported by  who clarified that dietary inclusion of ZONPs at a dose of 20 ppm resulted in a significant reduction in the serum TG and uric acid concentration, while serum HDL level was significantly higher as compared with control broiler group.Also,supplementation of growing Japanese quail diets with Nano zinc at levels of 0.2 and 0.3 g/kg diet significantly decreased total cholesterol and LDL levels and had the highest value for HDL in the serum as compared to control . In similar direction, serum total cholesterol and TG decreased significantly and activities of liver enzymes (AST and ALT) remained unchanged in the serum of Japanese quail fed ZnO-NPs at 30 or 60 mg / kg compared to the control .
The same trend was found in laying hens  and in broilers [33,68] current results also came in accordance with  records a reduction in cholesterol, TG, creatinine, uric acid and increased HDL with the supplementation of ZONPs at level of 20 or 40 mg /kg diet.
Present results are in close agreement withreport by  indicated that there was no significant difference in glucose levels and significantly decreased serum total cholesterol, triglyceride and very low-density lipoprotein (VLDL) by dietary supplementation of ZONPs to broiler chicks. This result could be attributed to the ability of Zn to induce glucagon secretion and suppress insulin secretion . Significant improvements were observed in the health status (low blood cholesterol level and high ALT) of the birds by supplementing NZn to broiler diets at 0.06 mg/kg [71,72].
The significant increase in serum HDL and reduced blood serum TG and cholesterol in the present study is parallel with two previous study by the same author [29,73] on laying hen and broiler respectively administrated ZONPs. This finding may be due to the improvement in calories and fat intake after zinc supplementation and the fact that zinc’s role in enzymes systems, in that zinc forms an integral part of several enzymes (metalloenzymes), which plays a vital role in fat metabolism responsible for lipid digestion and absorption [74-79].
The decrease in cholesterol may be due to that Zn prevent cholesterol from absorption in gastro intestinal tract  and may promote the growth and activity of lactic acid bacteria, which reduces the cholesterol level by producing enzymes disintegrating bile salts and making them unconjugated .
On the other hand, present results came in contradictions with the data obtained by  indicated that the supplementation broiler diet with Nano-ZnO had no significantly affects the ALT and AST activates and increased serum cholesterol level. Possible reason for these differences is probably related to using doses and time of animal exposed to the Nano zinc, as, it has been reported that, level above 50 mg/kg of ZONPs increase the plasma level of ALT and AST .
Tissue Zinc concentrations.
The ability of Nano minerals to pass through the small intestine and distribute in the body are much greater than inorganic and organic minerals . The Zn concentration in tissues and serum is often used as an indicator of the Zn status and storage in the body of animals as well as the level of Zn consumed by birds because low values are considered an early symptom of zinc deficiency [84,85].
Present study show that there were significant differences among treatments in the Zn concentration of liver, serum, breast and thigh muscles. Supplementation of ZONPs at both two dose supplementation increased amount of Zn in serum and all tissues examined compared with the control group and these increase linearly with increasing dietary ZONPs levels. These resultscame in agreement withthosereported in broilers by [44,63,86] and in layers by [7, 55, 87-89] where, the highest levels of zinc were detected in the livers, serum and muscles of birds fed a supplemented ration with ZONPs when compared with control one.Also, in Pekin ducksby reported that zinc accumulation in plasma, breast muscle and liver were linearly increased with increasing zinc supplementation.
Additionally, in Japanese quails by  observed thatinclusion of ZONPs in the diet of Japanese quails induceda significant increase in the zinc concentration in liver compared to the control. They added that liver tissue retained a higher zinc concentration and the highest dose of ZONPs (60 mg/kg diet) was exclusively able to induce a significant increase in the concentration of zinc in the serum of Japanese quail. Similar results were obtained in rabbit by  who indicated thatnZnO supplementation at 30 and 60 mg / kg, significantly increased hepatic and serum zinc concentrations, which partly supported better absorption of nZnO and subsequently the positive relationship between nZnO supplementation and growth performance of rabbits.
The liver is an organ in the body that processes blood and helps to remove unwanted substances. Several studies indicates that Zn in the form of nanoparticles is able to penetrate into the hepatic cells via blood or interstitial space and being the liver as the main organ of Zn metabolism [63,92]. In addition, another theory that supports accumulation of Zn in the liver may be the activity of metallothionein, a cysteine-rich protein with the ability to bind divalent cations and control the pool and turnover of the microelements . In this respect,  reported that dietary Zn supplementation linearly increases plasma and liver Zn concentrations in broilers. It is proved that the liver is sensitive to Zn supplementation because this organ acts as a Zn reservoir in the body, thus, it is expected that the birds receiving treatments supplemented with Zn should have a higher content of this element in their liver .
Furthermore, in two studies reported by the same author [96,97] it was indicated that an increase in Zn supplementation increased Zn content in broiler organs, in which the highest amount was observed in liver, thigh muscle, and breast muscle, respectively They also postulated that compared with breast muscle, the thigh muscle responded positively to dietary Zn supplementation, which is consistent to present study.
In this respect, present results are in line with [98-100] as Zinc content in chicken thigh is known to be higher than in breast. The same results were also reported by,where the concentration of zinc varies in tissues and the reason for this difference is due to the morphology, biochemical and functional state of the tissues. Additionally, according to  illustrated that the increase in serum Zn levels is related to the higher absorption and lower interaction with other complexed minerals in the digestive tract increasing the bioavailability of Zn bound to amino acids/proteins, and therefore it is easily absorbed because of such structures.
Earlier results revealed that the retention of zinc in the body increased as the dosage level of nano zinc oxide increases. This may be due to nano form trace element enter the animal’s body through direct penetration. Therefore, its utilization rate will be much higher than that of the ordinary inorganic trace elements . Similarly,  also observed increased bioavailability of zinc in broilers when supplemented zinc in nano form as compared to birds fed with inorganic zinc. Moreover, the results of [33 , 57] revealed that Zn deposition was significantly increased in breast muscle and liver with dietary addition and/or substitution of inorganic Zn with nano Zn.
Furthermore, supplementation of nano-Zn (82.5 mg/kg diet) increased the Zn concentration in the liver of broilers compared to 110 mg/kg of ZnSO4 as microparticles .
Small intestine, its mucosal barrier in particular plays an essential role in absorption and maintaining health, preventing tissue injury and in ensuring adequate provision of dietary nutrients to the whole body. The height of villus and its ratio with crypt depth are most widely used as good indicators of mucosal integrity and intestinal function that correlated with better gut health and greater absorption of available nutrients [104,105].
Findings of this study inspected the impact of ZONPs supplement on the intestinal villi and intestinal crypt of tested broilers. Histological examination for the sections of intestine of broiler chicks fed a supplemented diet with 40 mg /kg ZONPs in the present study exhibited obvious desquamation of the intestinal villi, profound increase in cell production of intestinal villi and intestinal crypt, and aggregated lymphocytes. This was in consistent with the data recorded by  observed that dietary replacement of 60 mg inorganic zinc oxide with 45 and 30 mg of nano zinc/kg diet significantly increased villi length and width, crypt depth and villi length/crypt depth ratio compared with broiler chicks group fed on the basal diet with inorganic zinc oxide supplementation, which indicate improvement of absorptive capacity of different nutrients and improved feed efficiency. Also,  reinforced the pervious results when chicks fed diets with supplemental ZONPs at 50 ppm.
In a more comprehensive experimentconducted by  reported that supplementation of ZNOPs at the dose rate of 40 mg is a considerable feed additive for poultry with beneficial effects on intestinal changes. They showed a significant increase in villus height (VH), villus surface area (VSA) and total goblet cell (GC) count and villus height: crypt depth ratio (VH:CD) was also high in all parts of small intestine of 40 ZONPs supplemented birds. They clarified that the possible explanation for higher villus height may be due to higher bioavailability of zinc nanoparticles, so maintaining epithelial barrier integrity and function. The higher goblet cells could be another reason for higher villus height in intestinal segment, as acidic mucin is resistant to bacterial degradation resulting in less cellular damage 
Moreover, crypt development is essential to increase cell renewal rate and maturation in the gut. The increase in crypt depth of chicken supplemented with different levels of nano zinc/kg might provide more surface area for nutrient absorption by increasing enterocyte proliferation and intestinal mucin secretion because mucin-producing goblet cells are present mainly in the crypts .
The crypt plays a key role in the continuous renewal of villi because of its stem cell population whom continuous division throughout life allows replacement of villus epithelial cells . In this regard,  illustrated that the improved dimensions of villus may linked with increased absorptive surface and higher proliferation of crypt cells of the villus due to the supplementation of Zn. Also, it wasindicated that zinc repaired intestinal injury by reducing the apoptotic index of ileal epithelial cells, enhancing villus height and crypt depth.
It speculated that, upon oral exposure, the dose of the NPs is the chief feature controlling the intensity of tissue damage. As some doses could improve the performance parameters of broilers without significant fear on broilers health (The no-observed-adverse-effect level (NOAEL)) and other doses caused tissue damage besides affect broilers health . This can clarify the results of this study in the sections of intestine from the birds group fed supplemented diet with 60 mg ZONPs, they suffered from marked tissue degeneration, apoptosis of intestinal villi, and atrophy of intestinal crypt.
The liver has the critical job of maintaining the body’s metabolic homeostasis. This includes the processing of dietary amino acids, carbohydrates, lipids and vitamins, removal of microbes and toxins in splanchnic blood and route to the systemic circulation; synthesis of many plasma proteins; and detoxification and excretion into the bile of endogenous waste products and pollutants xenobiotics.
Present results were in line with the findings of  and  investigated the effect of high (900 mg/kg b.w.), intermediate (600 mg/kg b.w.) and low (300mg/kg b.w) concentrations of zinc on the histology of the liver of broiler chicks. Pronounced degenerative, apoptotic, and inflammatory changes found in all birds as compared to the controlled group. These resultssuggest that due to the more accumulation of zinc in the liver of the broiler chicks, the chicks possess more stress and severe histological changes in their liver because the liver is the important site for zinc accumulation. Also,  reported that the distinguished apoptosis could be progressed from intercellular stress generated by ZONPs. They were reported to induce also ap53 upregulation, dermal fibrosis, and increased cell cycle evolution.
Previous literature displayed that ZONPs could rise neutrophils numbers with attraction to some proteins such as immunoglobulin and lipoproteins . In this respect  attributed these pathological changes and their toxic effects to their solubility, resulting in increased intracellular Zn2+. Moreover, nanoparticles are expected to rise the existence of inflammation in diverse organs, consequently leading to the spreads of the inflammatory reactions . Watson et al.  added that the administration of ZONPs hindered Kupffer cell phagosomes motility and thus conduct the hepatic injury. In this respect, supplementation of zinc causes cirrhotic liver that leads to a decrease in collagen, fibrin and reticulin as reported by .
Findings in this study monitored the outcomes of ZONPs supplementation on the normal renal tissue of the examined broilers. Approaching control group, normal renal cortex structure emphasized with glomerular corpuscle, proximal convoluted tubules, distal convoluted tubules, and collecting tubules. 40 mg ZONPs broilers group displayed congested blood vessels, extravasation of blood cells between renal tubules and surrounding glomerular corpuscle, inflammatory cells infiltration, and epithelial desquamation and exudate noticed inside some tubules. Conversely, 60 mg ZONPs group highlighted degeneration of renal tissue including tubular disorganization and apoptotic cells, extravasated RBCS throughout tissue, and congestion in blood vasculature. This agreed with  who revealed that zinc oxide nanoparticles exerted a destructive effect on the kidney. Moreover, it was found that these nanoparticles had a toxic effect on the renal tissue at a high concentration. Proximal tube imperfections, RBC crowding, and leukocyte leak specify the damaging properties of ZONPs in low doses on renal tissue.
Furthermore,the results of  explained that the kidney tissue of animals treated with ZONPs exhibited apoptosis along with necrosis, the reduced glomerular diameters induced by ZONPs may be a result of enhancing cell death which leads to kidney weight loss.In the study of  attributed the DNA damage and cytotoxicity occurred in the kidney cells was due to oxidative stress induced by ZONPs by decreasing SOD and GPx enzymes activity and increasing MDA contents. Consequently, oxidative stress can stimulate apoptotic or necrotic cell death pathways .