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Organic or inorganic zinc in poultry nutrition: a review

Published online by Cambridge University Press:  27 October 2017

M.E. ABD EL-HACK Open the ORCID record for M.E. ABD EL-HACK [Opens in a new window] ,
M. ALAGAWANY ,
M. ARIF ,
M.T. CHAUDHRY ,
M. EMAM  and
A. PATRA
M.E. ABD EL-HACK*
Affiliation:
Departmentof Poultry, Faculty of Agriculture, Zagazig University, Zagazig 44511, Egypt
M. ALAGAWANY
Affiliation:
Departmentof Poultry, Faculty of Agriculture, Zagazig University, Zagazig 44511, Egypt
M. ARIF
Affiliation:
Department of Animal Sciences, University College of Agriculture, University of Sargodha, 40100, Pakistan
M.T. CHAUDHRY
Affiliation:
Institute of Animal Nutrition, Northeast Agricultural University, Harbin 150030, China
M. EMAM
Affiliation:
Department of Nutrition and Clinical Nutrition, Faculty of Veterinary Medicine, Damanhour University, Damanhour 22516, Egypt
A. PATRA
Affiliation:
Department of Animal Nutrition, West Bengal University of Animal and Fishery Sciences, Belgachia, Kolkata, India
*
Corresponding author: m.ezzat@zu.edu.eg, dr.mohamed.e.abdalhaq@gmail.com

Abstract

Zinc (Zn) is an essential component in animal and poultry metabolism of various biochemical pathways. It serves as a nutrient and also as a feed additive for improving reproductive functions, productive indices, cellular immunity, normal growth and the maintenance of feathers, bone tissues as well as appetite. Furthermore, Zn has many roles as an antioxidant agent. This mineral is essential for hormone function, including pancreatic (insulin and glucagon), sex and growth hormones. It is a part of more than 300 enzymes that are involved in the metabolism of protein, energy, carbohydrates and nucleic acids. Previous studies demonstrated many beneficial impacts of supplemental Zn on different physiological and immunological functions above the established concentration in diets, including alleviating heat stress. Zinc supplementation in layer diets increases albumen weight, and may alter egg shell thickness and total egg weight. Zinc deficiency can cause a fraying of the feathers and retardation in growth of broilers. Different Zn sources (organic or inorganic) positively impact health and performance in poultry including meat or egg production, feed intake and conversion efficiency, carcass traits, blood parameters and apparent nutrient digestibility. This review compares and provides a review of the nutritional and physiological aspects of different Zn sources.

Keywords

zincorganicinorganicpoultrynutritionproductionhealth

Information

Type
Reviews
Information
World's Poultry Science Journal , Volume 73 , Issue 4 , December 2017 , pp. 904 - 915
Copyright
Copyright © World's Poultry Science Association 2017 

Introduction

Zinc (Zn) is an important nutrient required in poultry nutrition for various biological functions (Olgunand Yildiz, 2016). It has many activities in animal tissues as an antioxidant through the synthesis of metallothioneine (Naz et al., Reference NAZ, IDRIS, KHALIQUE, ALHIDARY, ABDELRAHMAN, KHAN, CHAND, FAROOQ and AHMAD2016) and as a component of DNA and RNA polymerase enzymes. In this respect, Weser et al. (Reference WESER, SEEBER and WARNECKE1969) found increased RNA synthesis in rats injected with higher levels of Zn without any deficiency after a partial hepotectomy. The same authors reported that Zn injection into deficient rats elevated the synthesis of DNA. Zinc potentiates the activity of some hormones including glucagon, insulin, sex and growth hormones. It forms part of more than 300 enzyme systems that are involved in energy, carbohydrates, nucleic acids and protein metabolism. In addition, it plays a substantial role in the immune system, and in the transport and the use of vitamin A (Chand et al., Reference CHAND, NAZ, KHAN, KHAN and KHAN2014).

Recommended requirements for Zn by poultry (40 mg/kg of diet) are mainly based on the performance criteria for broiler chickens (NRC, 1994), and can be supplemented from inorganic or organic sources. The main difference between these source compounds is that most inorganic compounds do not have carbon; however organic compounds always contain carbon (Jahanian and Yaghoubi, Reference JAHANIAN and YAGHOUBI2010) and have carbon-hydrogen bonds (C-H). Inorganic minerals, such as sulphates and oxides, are usually supplemented in poultry rations above the recommended NRC requirement to improve feed utilisation and maximize production performances (Leeson and Caston, Reference LEESON and CASTON2008). There are two inorganic feed-grade Zn sources in a commercial sense, which are utilised by the poultry feed industries (Leeson and Summers, Reference LEESON and SUMMERS1997): Zn oxide (ZnO: 72% Zn) and Zn sulphate monohydrate (ZnSO4-H2O: 36% Zn). Most (80-90%) of the supplemental Zn used in poultry diets comes from ZnO source, which is less bioavailable than Zn sulphate for poultry (Sandoval et al., Reference SANDOVAL, HENRY, AMMERMAN, MILES and LITTELL1997). However, the sulphate (acid salt) is more water soluble, allowing reactive metallic ions to promote free-radical formation. This can support in chemical reactions responsible for the breakdown of vitamins and eventually the destruction of fats and essential oils, down rating the nutritive value of the diets. Oxides are less reactive, but are again less bioavailable (Batal et al., Reference BATAL, PARR and BAKER2001). The organic sources, for example Zn-methionine or Zn-propionate, are more bioavailable than inorganic sources (Rahman et al., Reference RAHMAN, WAHED, FCHS, BAYUI and ALVAREZ2002), and they can give better results in terms of poultry health and performance. This review focuses on the impacts of different sources and concentrations of dietary Zn supplementation for the production and nutritional responses in poultry.

The role of Zn in poultry nutrition

Zinc exists in all living organisms and acts both catalytically and structurally in metalloenzymes (O'Dell, Reference O'DELL1992), which are recognised in all six enzyme kinds, which involve isomerase, transferase, oxidoreductase, lyase, ligase and hydrolase (Park et al., Reference PARK, BIRKHOLD, KUBENA, NISBET and RICKE2004). The necessity of Zn comes from its importance for normal growth and maintenance. It is required for other functions, like bone development, feathering, enzyme structure and function and appetite regulation (Batal et al., Reference BATAL, PARR and BAKER2001; Jahanian and Rasouli, Reference JAHANIAN and RASOULI2015). Stefanidou et al. (Reference STEFANIDOU, MARAVELIAS and DONA2006) stated that Zn has three major roles in the biological functions; structural, catalysts or regulatory, and Suttle (Reference SUTTLE2010) reported that it is an essential co-factor for several enzymes.

Zinc has been postulated to have a stimulatory impact on mineralisation, formation of bone and the preservation of bone mass. The metal activates directly aminoacyl-tRNA synthetase in osteoblastic cells, and it activates synthesis of cellular protein. Furthermore, Zn deactivates osteoclastic bone resorption through inhibiting osteoclast-like cell formation from marrow cells (Yamaguchi, Reference YAMAGUCHI1998).

Proteins and Zn-binding domains make up around 10% of proteome in animals (Andreini et al., Reference ANDREINI, BANCI, BERTINI and ROSATO2006). Zinc is a component of 1000 transcription proteins, and it has been suggested that the alteration in Zn status affects the gene expression of a plenty of genes by activation (Ho et al., Reference HO, DAVIS, RITCHIE and WALDOR2003). As a reflection of its role in gene regulation, it is required for the synthesis of different proteins. Two key structure proteins, keratin and collagen, both require Zn (Suttle, Reference SUTTLE2010). Any deficiency leads to decreased keratin and collagen formation leading to some deficiency signs such as poor feathering in poultry, bone abnormality, decreased tissue strength and dermatitis (Lesson and Summers, Reference LESSON and SUMMERS2001). Turnover rate of collagen may be decreased as the metalloprotease may decrease in the tissues (Suttle, Reference SUTTLE2010).

A number of biochemical studies have shown how Zn insufficiency in poultry is manifested. Low blood Zn had been observed, and several enzymes activity in the metabolic pathways decreased in deficient animals. Supplementing Zn at level of 0.12 - 0.18 g/kg on a total-weight basis is common in all formulated poultry diets (Batal et al., Reference BATAL, PARR and BAKER2001). Zinc should be supplemented according to the requirements to prevent any deficiency problems (Jahanian and Rasouli, Reference JAHANIAN and RASOULI2015). The NRC (1994) recommends 40 mg/kg feeds for broilers, but usually practical poultry rations contain the double the recommended concentration (80 mg/kg). The uncontrolled transfer of Zn from animals to accumulate in the soil and water to croplands started to be one of the threatening hazard factors in recent decades (Batal et al., Reference BATAL, PARR and BAKER2001). Although environmental concerns have focused on phosphorus and nitrogen pollution of soils from poultry manure applications, many geographic regions are vulnerable to the pollution by metals such as Zn. Such pollution with metals like Cu and Zn has been accompanied by declined crop yields of maize, sorghum and bush beans (Burrell et al., Reference BURRELL, DOZIER, DAVIS, COMPTON, FREEMAN, VENDRELL and WARD2004).

Researchers (Jahanian et al., Reference JAHANIAN, NASSIRIMOGHADDAM and REZAEI2008a; Reference JAHANIAN, NASSIRIMOGHADDAM, REZAEI and HAGHPARAST2008b) have reported a higher bioavailability for organic Zn sources than that of inorganic forms (oxide and sulphate). Organic Zn sources have become a component in more recent diets used in feed industry. Nassiri Moghaddam and Jahanian (Reference NASSIRI MOGHADDAM and JAHANIAN2009) found that poultry diets fortified with Zn-methionine (ZnMet) replacing inorganic sources increased the immune response production titres against infection bronchitis disease and Newcastle infections. Similar results were observed when ZnMet or Zn-Lys was added to the diets of broilers (Jahanian and Yaghoubi, Reference JAHANIAN and YAGHOUBI2010), demonstrating higher bioavailability of these sources. Organic Zn has benefits from an environmental point of view. It helps to minimise levels in the environment due to its high bioavailability, which allows better absorption and utilisation of nutrients in the animal, allowing lower levels in feed and reduced excretion without compromising performance (Mohammadi et al., Reference MOHAMMADI, GHAZANFARI, MOHAMMADI-SANGCHESHMEH and NAZARAN2015).

Impacts of Zn on poultry

A number of researchers have used organic Zn (Burrell et al., Reference BURRELL, DOZIER, DAVIS, COMPTON, FREEMAN, VENDRELL and WARD2004) in broiler diets and found an increase in body weight and body weight gain. Higher biological efficacy of ZnMet in terms of increase in the growth was observed if Zn is bound by fibre and phytates in basal diets (Jahanian et al., Reference JAHANIAN, NASSIRIMOGHADDAM and REZAEI2008a; Reference JAHANIAN, NASSIRIMOGHADDAM, REZAEI and HAGHPARAST2008b). Ao et al. (Reference AO, PIERCE, POWER, DAWSON, PESCATORE, CANTOR and FORD2006) observed that a chelated Zn proteinate (Bioplex® zinc) increased body weight gain and feed intake with increasing levels (from 5 to 40 mg/kg diet). The study concluded that supplemental Zn required for optimal broiler growth rate during starting phase (1-21 days of age) was 9.8 mg/kg diet. Moreover, Jahanian et al. (Reference JAHANIAN, NASSIRIMOGHADDAM and REZAEI2008a) conducted an experimental trial to investigate the potential of dietary organic sources (Zn-lysine, Zn-methionine and Zn-acetate) on the broiler performance and carcass traits. The result showed a significant increase in the feed intake with organic Zn inclusion, while the overall feed conversion improved with 80 mg organic Zn/kg diet. Liu et al. (Reference LIU, LI, LU, XIE, ZHANG, WANG and LUO2013) stated that Zn proteinate had a significant beneficial effect on weight gain in broilers. Recently, Jahanian and Rasouli (Reference JAHANIAN and RASOULI2015) observed that partial substituting of inorganic Zn by ZnMet improved (P<0.01) the weight gain of broilers.

Different trends were reported by other researchers. Hudson et al. (Reference HUDSON, FAIRCHILD and WILSON2004) stated that organic Zn supplemented above NRC (1994) levels of 40 mg/kg had no impact on body weight of broiler breeders. Feng et al. (Reference FENG, MA, NIU, WU and WANG2010) performed an experiment with high level of Zn glycine (zinc glycine chelate, C4H8N2O4Zn) at 90-120 mg/kg added to the basal diet of broilers. No significant differences were found between the 120 ppm levels and inorganic Zn sulphate. In the same context, Bun et al. (Reference BUN, GUO, GUO, JI and CAO2011) conducted an experiment on the potential of organic Zn (methionine hydroxyl analogue-Zn chelate) on the performance of broilers challenged with Eimeria tenella. They found no effect on growth. Sunder et al. (Reference SUNDER, VIJAY KUMAR, PANDA, RAJU and RAMA RAO2012) investigated the effect of organic zinc and manganese supplementation on growth performance, tissue mineral uptake and immune status in broiler chickens. The results showed that supplementing organic Zn and manganese did not affect the performance parameters in broiler chickens up to 35 days of age. Wang et al. (Reference WANG, YU, WU, ZHANG, CUI, WAN and GAO2016) evaluated a Zn-pectin oligosaccharide chelate (Zn-POS; containing 7% Zn) in a corn-soybean based diet (80 mg/kg of Zn) for broiler chickens, supplemented at the rate of 300, 600 and 900 mg/kg. They reported that body weight gain increased with 600 mg/kg of Zn-POS compared with the control and other treatments, although final body weight was similar among the treatments. Furthermore, Yalcinkaya et al. (Reference YALCINKAYA, CINAR, YILDIRIM, ERAT, BASALAN and GUNGOR2012) found no effect on broiler weight gain with dietary organic Zn. Supplementation with Zn-acetate (Applichem, Germany) at the dose of 30 mg Zn/ kg diet increased body weight gain in broiler chickens fed a corn-soybean-wheat diet compared with a basal diet (without Zn supplementation) (Norouzi et al., Reference NOROUZI, DANESHYAR and FARHOOMAND2013). Yogesh et al. (Reference YOGESH, DEO, SHRIVASTAVA, MANDAL, WADHWA and SINGH2013) did not find significant effects on the performance of broiler chickens fed diets containing organic Zn proteinate. Leeson (Reference LEESON2005) reported that broiler chickens fed on diets supplemented with 14 mg/kg Zn as Bioplex® Zn had similar growth performance and mortality as the chickens fed on diets added at the commercial level (100 mg/kg) of zinc sulphate during a 42 day period. Ao et al. (Reference AO, PIERCE, PESCATORE, CANTOR, DAWSON, FORD and PAUL2011) compared the organic (Bioplex® Zn) versus inorganic Zn sulphate on performance of chickens. Those fed the maize-soybean basal diet (30-31 mg Zn/kg) or that supplemented with 12 mg of Zn sulphate had lower feed intake, weight gain and tibia Zn content than other treatment groups. The basal diet supplemented with 12 and 24 mg of organic Zn in starter and grower phase resulted in similar performance and tibia Zn content as those fed 40 mg of Zn as sulphate, and the equal performance but higher tibia Zn content than those given 12 mg of Zn as organic over the 42 days.

Mohanna and Nys (Reference MOHANNA and NYS1999a) compared two sources of ZnMet with Zn-sulphate in broiler chicken diets formulate to contain 20 to 90 mg/kg. They reported that 45 mg/kg was sufficient to maintain normal broiler performance at 21 d of age and sources had no effect on growth performance. From the literature, it appears that sources of Zn have little influence on growth performance when an optimum concentration of Zn is present in the diets, but low concentrations of organic Zn could be added to obtain the same performance.

Many studies have been performed to examine the impact of different organic zinc sources on poultry feed intake and conversion efficiency. Hess et al. (Reference HESS, BILGILI, PARSONS and DOWNS2001) added 40 mg/kg zinc from three different sources (ZnMet, Zn-Lys or ZnMet plus Zn-Lys) to broiler diets. They found improved FCR when organic zinc-amino acid complexes were used in feed for female broilers. The better FCR was observed in earlier weeks (1.66 in average for zinc amino acid complexes vs. 1.73 for the control); this may be attributed to proper feathering, as reported by Jahanian et al. (Reference JAHANIAN, NASSIRIMOGHADDAM and REZAEI2008a).

Nollet et al. (Reference NOLLET, VAN DER KLIS, LENSING and SPRING2007) observed an improvement in FCR in the starter period until 14 days of age in Ross broiler chicks fed supplemental organic minerals (Bioplex® Mn, Zn, Fe, and Cu) compared to the control. Amira (Reference AMIRA2009) indicated that broiler chicks fed diets containing BioZinc (commercial ZnMet) had a significant increase in feed consumption. In the same context, Liu et al. (Reference LIU, LI, LU, XIE, ZHANG, WANG and LUO2013) observed that broilers fed the diets enriched with Zn proteinate (10, 20, 40, or 80 mg/kg) had higher (P=0.048) average daily feed intake and higher (P=0.106) average daily gain than the control. Supplementation with Zn-acetate (Applichem, Germany) at the dose of 30 mg/kg in the diet increased daily feed intake and improved FCR in broiler chickens fed a corn-soybean-wheat diet compared with a basal diet with no Zn supplementation (Norouzi et al., Reference NOROUZI, DANESHYAR and FARHOOMAND2013). A basal diet (containing 20 mg/kg Zn) supplemented with up to 40 mg/kg increased food intake at 25 mg Zn/kg and improved feed efficiency at 40 mg Zn/kg diet without any influence of source of Zn (Mohanna and Nys, Reference MOHANNA and NYS1999a). Wang et al. (Reference WANG, YU, WU, ZHANG, CUI, WAN and GAO2016) reported that average daily feed intake increased without affecting feed efficiency due to supplementation of 600 mg/kg of organic Zn-POS compared with the basal control diet (80 mg/kg) and other treatments (300 and 900 mg/kg of Zn-POS).

In laying hens, Bahakaim et al. (Reference BAHAKAIM, ABDEL MAGIED, OSMAN, OMAR, ABDELMALAK and RAMADAN2014) found that supplementing organic zinc (ZnMet) did not affect feed consumption from 24-28 weeks of age, but increased feed intake significantly during the second and third periods (28-32 and 32-36 weeks of age). However, Burrell et al. (Reference BURRELL, DOZIER, DAVIS, COMPTON, FREEMAN, VENDRELL and WARD2004) showed that adding Zn to broiler chick diets at 0, 20, 40, and 80 mg/kg as ZnSO4 had no effect on feed conversion ratio. Recently, Jahanian and Rasouli (Reference JAHANIAN and RASOULI2015) stated that partial replacement (50%) of inorganic sources by ZnMet had no significant (P>0.05) impact on feed intake, but complete replacement increased (P<0.05) feed consumption during the starter and grower periods over the entire (1-42 days) experimental period.

Carcass is an important measurement for meat-type birds. Jahanian et al. (Reference JAHANIAN, NASSIRIMOGHADDAM and REZAEI2008a) observed that the breast meat yield increased with organic zinc inclusion (40, 80 or 120 mg/kg). Organic supplementations led to a significant increase in liver, breast and carcass weight percentages. El-Husseiny et al. (Reference EL-HUSSEINY, HASHISH, ALI, ARAFA, ABD EL- SAMEE and OLEMY2012) stated that organic Zn, Mn, and Cu supplement at 50% of recommended requirements showed an improvement in carcass characteristics without any effect on edible parts, compared to the birds in the control group. Yalcinkaya et al. (Reference YALCINKAYA, CINAR, YILDIRIM, ERAT, BASALAN and GUNGOR2012) stated that supplementing broiler diets with organic Zn increased relative organ weights (liver, pancreas, and spleen) compared to the birds fed diets containing inorganic. Jahanian and Rasouli (Reference JAHANIAN and RASOULI2015) stated that dietary replacement with ZnMet instead of inorganic Zn significantly improved relative weight of liver, decreased (P<0.01) abdominal fat and increased (P<0.05) carcass yield. From these studies, it appeared that supplementation of organic Zn replacing 50 to 100% inorganic Zn sources could improve carcass traits of broiler chickens.

Biochemical blood parameters are crucial indicators of nutritional and physiological status of birds and animals. Amira (Reference AMIRA2009) stated that the chicks fed diets with organic zinc (Biozinc) at 120, 80 or 40 mg/kg had significantly increased blood total protein and globulin compared to all other groups. Liu et al. (Reference LIU, LI, LU, XIE, ZHANG, WANG and LUO2013) found increased Zn concentration in the plasma of broiler chickens fed with a proteinate source. However, Yalcinkaya et al. (Reference YALCINKAYA, CINAR, YILDIRIM, ERAT, BASALAN and GUNGOR2012) showed no effects of the dietary organic Zn (80 mg/kg Bio-Plex®) on blood biochemical parameters, including aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase activities, triglyceride, glucose, total protein and total cholesterol in broiler chickens. Bahakaim et al. (Reference BAHAKAIM, ABDEL MAGIED, OSMAN, OMAR, ABDELMALAK and RAMADAN2014) showed that the addition of zinc in the organic form significantly increased plasma Zn concentrations, which could be attributed to better availability of ZnMet. Jahanian and Rasouli (Reference JAHANIAN and RASOULI2015) showed that partially replaced Zn source with Zn methionine caused a reduction P<0.01) in plasma uric acid, with no significant effect on levels in the blood of chickens. Norouzi et al. (Reference NOROUZI, DANESHYAR and FARHOOMAND2013) reported that Zn-acetate supplementation (Applichem, Germany) at a dose of 30 and 60 mg/kg diet decreased blood malondialdehyde concentration in chickens.

One of the most important goals for nutritionists is to improve digestibility of feedstuffs, which positively reflects on the performance of birds. Nollet et al. (Reference NOLLET, VAN DER KLIS, LENSING and SPRING2007) reported that broiler chickens fed 50% or 100% of Zn or Mn or Cu or Fe as proteinates following the breed recommendations showed a tendency to improve the digestion coefficients of dry matter (DM), organic matter (OM), ether extract (EE), crude fibre (CF) and nitrogen free extract (NFE) compared with those fed diets supplemented with 100% of the commercial recommendations for these four minerals as inorganic sulphates. Bao et al. (Reference BAO, CHOCT, IJI and BRUERTON2009) showed that supplementation of basal sorghum-soybean diets (21 to 23 mg Zn/kg and 15-18 mg Mn/kg) with 20 mg Zn plus 20 mg Mn as proteinates/kg diet increased protein digestibility compared with the unsupplemented control or the 10 mg Zn and Mn supplemented diets. However, higher concentrations (30 and 40 mg/kg each of Zn and Mn) did not further increase protein digestibility in broiler chickens at 28-35 days of age. Wang et al. (Reference WANG, YU, WU, ZHANG, CUI, WAN and GAO2016) studied Zn-POS chelate (containing 7% Zn) in corn-soybean based diets (80 mg/kg of Zn) for broiler chickens, supplemented at a rate of 300, 600 and 900 mg/kg Zn and noted that dry matter, energy and protein digestibility increased at 600 mg/kg of Zn-POS compared with the control. It seems that Zn supplementation can improve the utilisation of nutrients perhaps due to increased digestive enzyme activities and improved well-being of the birds.

To examine the impact of inorganic Zn on growth performance of broilers, Burrell et al. (Reference BURRELL, DOZIER, DAVIS, COMPTON, FREEMAN, VENDRELL and WARD2004) observed that supplementing corn-soybean meal diets (30 mg Zn/kg) with 40, 60 and 80 mg/kg of inorganic Zn progressively increased growth performance in broilers. Likewise, Feng et al. (Reference FENG, MA, NIU, WU and WANG2010) showed that adding Zn at a high level (120 mg/kg) in the form of Zn sulphate to the control diet improved growth performance of broilers. Saenmahayak et al. (Reference SAENMAHAYAK, BILGILI, HESS and SINGH2010) compared three treatments 1) control (80 mg Zn/kg from ZnSO4); 2) 40 mg Zn/kg from ZnSO4 and 40 mg Zn/kg Zn complex; 3) 80 mg Zn/kg from ZnSO4 and 40 mg/kg from Zn complex. Growth performance parameters were improved for diets 2 and 3 compared to the control. On the other hand, Gheisari et al. (Reference GHEISARI, RAHIMI-FATHKOOHI, TOGHYANI and GHEISARI2010) showed no significant effects for Zn oxide or Zn sulphate supplementation on the body weight of broilers. In agreement, Sunder et al. (Reference SUNDER, VIJAY KUMAR, PANDA, RAJU and RAMA RAO2012) showed that Zn supplementation (ZnSO4-7H2O) to broiler basal diet (free of Zn supplementation) at a gradual level had no significant influence on body weight.

In Japanese quail, Sahin et al. (Reference SAHIN, SMITH, ONDERCI, SAHIN, GURSU and KUCUK2005) showed that Zn supplementation as ZnSO4-H2O in three levels (0, 30 and 60 mg/ kg diet) increased body weight gain.

However, Attia et al. (Reference ATTIA, ABD AL-HAMID, ZEWEIL, QOTA, BOVERA, MONASTRA and SAHLEDOM2013) evaluated the potency of inorganic (ZnO) or organic Zn supplementation in diets (containing basal levels of 26 mg/kg) at graded levels (30, 60 and 120 mg/kg) for ducks. Body weight significantly increased for ducks fed diets containing up to 60 mg/kg during the trial period (1-56 days of age). Interestingly, ZnO increased growth performance and improved feed conversion compared to the organic Zn in this study. El-Husseiny et al. (Reference EL-HUSSEINY, ABD-ELSAMEE, OMARA and FOUAD2008) reported that high doses (175 mg/kg ZnO) increased egg production and decreased egg shell-thickness without any effect on egg mass compared with a low dose of Zn (75 mg/kg).

To investigate the impact of different inorganic Zn sources on feed intake and efficiency in poultry diets, several studies were conducted. Kucuk et al. (Reference KUCUK, SAHIN and SAHIN2003). They noted that Zn addition (30 mg/kg) in the sulphate form (ZnSo4-H2o) to a basal diet (free of Zn supplementation) improved FCR in broiler chicks. Gheisari et al. (Reference GHEISARI, RAHIMI-FATHKOOHI, TOGHYANI and GHEISARI2010) reported that the best FCR was found in birds fed the highest dose of inorganic Zn (as oxide and sulphate forms). Ao et al. (Reference AO, PIERCE, PESCATORE, CANTOR, DAWSON, FORD and PAUL2011) reported that broilers fed a control diet (30-31 mg/kg Zn) or a diet with 12 mg of Zn in the form of sulphate had lower (P<0.05) feed intake and weight gain than broiler chicks fed 40 mg /kg during whole growing phase (1 to 42 days). However, during the starter phase (1 to 21 days), feed intake and body weight gain were lower for the control treatment only. Jahanian and Rasouli (Reference JAHANIAN and RASOULI2015) found that ZnO supplementation caused more (P<0.01) feed consumption (7% higher compared to control) in broiler chicks. FCR was not improved with higher supplementation Zn from either organic or inorganic sources (Ao et al., Reference AO, PIERCE, PESCATORE, CANTOR, DAWSON, FORD and PAUL2011). High doses (175 mg/kg) of ZnO decreased feed intake and feed efficiency compared with the low doses (75 to 140 mg/kg diet) in laying hens (El-Husseiny et al., Reference EL-HUSSEINY, ABD-ELSAMEE, OMARA and FOUAD2008). In Japanese quail, Sahin et al. (Reference SAHIN, SMITH, ONDERCI, SAHIN, GURSU and KUCUK2005) stated that ZnSO4-H2O at different levels had significantly increased feed intake (by 2%) and improved feed efficiency (by 0.45%). In ducks, Attia et al. (Reference ATTIA, ABD AL-HAMID, ZEWEIL, QOTA, BOVERA, MONASTRA and SAHLEDOM2013) stated that during the trial period (1- 56 days of age), FCR, but not feed intake, improved for those fed diets supplemented with ZnO compared with the organic Zn source.

Sunder et al. (Reference SUNDER, PANDA, GOPINATH, RAMA RAO, RAJU, REDDY and VIJAY KUMAR2008) found no significant impact with supplementation of Zn (ZnSO4-7H2O) to a basal diet at various levels (10, 20, 40, 80, 160, or 320 mg/kg) on various carcass traits in broilers. However, Gheisari et al. (Reference GHEISARI, RAHIMI-FATHKOOHI, TOGHYANI and GHEISARI2010) stated that inorganic Zn supplementation had a significant (P<0.05) effect on carcass traits of broilers at 49 days of age. Broilers fed Zn in a sulphate form had a significantly (P<0.05) higher carcass yield than those fed ZnO. Saenmahayak et al. (Reference SAENMAHAYAK, BILGILI, HESS and SINGH2010) stated that absolute breast yields were higher in broilers fed 80 ppm ZnSO4 and 40 ppm complexed Zn in comparison to the control (80 ppm of ZnSO4). Liu et al. (Reference LIU, LU, LI, ZHANG, XY, ZHANG and LUO2011) showed that birds fed diets supplemented with inorganic Zn (10, 20, 40, or 80 mg of Zn/kg) had a higher percentage of giblets yield than birds fed the unsupplemented control diet. Jahanian and Rasouli (Reference JAHANIAN and RASOULI2015) stated that supplementation with ZnO increased both breast and body yields of broilers.

Several studies investigated the impact of inorganic Zn on blood chemistry. Lu and Combs (Reference LU and COMBS1998) found that Zn supplementation did not affect serum cholesterol levels in chickens. In the same context, Fawzy et al. (Reference FAWZY, EL-SADAWI, EL-DIEN and MOHAMED2016) found that Zn oxide decreased triglycerides and increased high density lipoprotein (HDL) and cholesterol concentrations. Contradicting results were obtained by Al-Darji and Amen (2011) who noted that the addition of inorganic Zn to diets of broiler breeder chickens (50, 75 and 100 mg/kg) resulted in a significant increase in blood plasma total cholesterol.

Sahin et al. (Reference SAHIN, SMITH, ONDERCI, SAHIN, GURSU and KUCUK2005) observed that supplementing Japanese quail diets with ZnSO4 did not impact blood serum content MDA or vitamins C, E, and A concentrations. Bartlett and Smith, (Reference BARTLETT and SMITH2003) found that dietary inorganic Zn levels did not affect plasma Zn concentration in chickens reared under heat stress, and Bahakaim et al. (Reference BAHAKAIM, ABDEL MAGIED, OSMAN, OMAR, ABDELMALAK and RAMADAN2014) found that ZnSO4 decreased plasma Zn compared with the control group. Mohanna and Nys (Reference MOHANNA and NYS1999a) noted that tibia and plasma Zn concentrations increased linearly with Zn dietary content and reached a plateau at 75 mg/kg, whereas whole body Zn was saturated when the dietary Zn content was 90 mg/kg, but Zn sources from organic or inorganic had no influence on the Zn concentration in plasma or whole body.

Sahin and Kucuk (Reference SAHIN and KUCUK2003) in their study on laying Japanese quails confirmed that supplementing the diet with Zn sulphate (30 or 60 mg /kg diet) increased (P<0.05) digestibility of dry matter, organic matter, crude protein and ether extract compared with the control. In a study by El-Husseiny et al. (Reference EL-HUSSEINY, ABD-ELSAMEE, OMARA and FOUAD2008), corn-soybean layer diets containing 9 mg/kg Zn was supplemented with different doses (70, 105, 140 and 150 mg/kg) of ZnO. High doses (140 and 175 mg/kg diet) generally decreased the dry matter, organic matter and nitrogen-free extract digestibility, but increased protein digestibility compared with low doses (75 and 105 mg/kg). Sridhar et al. (Reference SRIDHAR, NAGALAKSHMI, SRINIVASA RAO and RAMA RAO2015) compared inorganic Zn (ZnO; 40 mg/kg) and organic Zn (Zn glycinate; 10-30 mg/kg) in maize-soybean based diet in broiler chickens for nutrient utilisation, and found that digestibility of different nutrients was similar among the groups. Zn has a useful role in pancreatic tissue preventing oxidative damage and activates pancreatic secretions of digestive enzymes and consequently stimulates the digestibility of nutrients (Sahin et al., Reference SAHIN, SMITH, ONDERCI, SAHIN, GURSU and KUCUK2005).

Interaction of Zn and phytase supplementation

Phytate is widely distributed in plants, which is the primary storage form of phosphorus. Phytate forms insoluble complexes with phosphorus, Zn and other minerals, and limits its availability in non-ruminant species (O'Dell et al., Reference O'DELL, YOHE and SAVAGE1964). Therefore, phytase supplementation in the broiler diets increases the bioavailability of different minerals including P, Zn and Mn (Ghosh et al., Reference GHOSH, MANDAL, ROY and PATRA2016). Yi et al. (Reference YI, KORNEGAY and DENBOW1996) suggested that 0.9 mg of Zn could be released per 100 FTU of phytase over the range of 150 to 600 FU of phytase. Similarly, Jondreville et al. (Reference JONDREVILLE, LESCOAT, MAGNIN, FEUERSTEIN, GRUENBERG and NYS2007) showed that 1 mg of zinc as sulphate can be spared per 100 FTU, up to a maximum of 850 FTU. Therefore, phytase supplementation is expected to interact with Zn concentration in diets. In this line, Ao et al. (Reference AO, PIERCE, PESCATORE, CANTOR, DAWSON, FORD and SHAFER2007) showed interactions between phytase (0 and 500 FTU/kg) and organic Zn supplementation (0, 2, 4, 8, 16, and 32 mg/kg Zn from Bioplex® Zn). The organic Zn supplementation linearly improved feed intake, growth, feed efficiency, tibia Zn and tibia ash concentration. The authors suggested that 12 mg/kg of supplemental Zn without phytase and 7.4 mg/kg supplemental Zn with phytase were required for the optimal weight gain of chicks. In chicks, Yi et al. (Reference YI, KORNEGAY and DENBOW1996) observed a linear response of bone and liver Zn to graded levels of phytase up to 600 FTU/kg maize-soya isolate diet. In another study, Świątkiewicz et al. (Reference ŚWIĄTKIEWICZ, KORELESKI and ZHONG2001) studied two sources of Zn (organic amino acid complex versus ZnSO4) with 0, 10, 20, and 40 mg/kg of Zn and without or with phytase supplementation in broiler chickens fed wheat-soybean meal based diets (44 mg Zn/kg) for a period of 28 days. Phytase and Zn interaction effects were noted for body weight gain, feed efficiency and tibia Zn content, but not for feed intake. In this study, source of Zn did not affect any growth performance variables; whereas phytase supplementation improved growth rate and feed efficiency. Improvements in zinc availability by microbial phytase added to low zinc diets fed to chicks have previously been reported (Thiel et al., Reference THIEL, WEIGAND, HOPPE and SCHONER1993; Mohanna and Nys, Reference MOHANNA and NYS1999b). In some instances, no effect of microbial phytase on zinc availability was observed because of the high zinc levels in the experimental diets (Thiel et al., Reference THIEL, WEIGAND, HOPPE and SCHONER1993; Sebastian et al., Reference SEBASTIAN, TOUCHBURN, CHAVEZ and LAGUE1996; Mohanna and Nys, Reference MOHANNA and NYS1999b). Overall, studies suggested that phytase supplementation up to a limit (600-850 FTU) can spare some portion (6 to 8 mg) of Zn from both organic or inorganic sources, which would lead to decreased Zn excretion in to the environment.

Conclusions

Zinc plays several roles in metabolism and nutrient utilisation in poultry. It serves as an essential nutrient and acts as a metal cofactor for several enzymes. Dietary Zn supplementation, either from organic or inorganic sources above the recommended levels, may positively impact bird's appetite, productive and reproductive efficiency, skeletal and skin health. The majority of studies in this respect confirmed that organic Zn sources like ZnMet or Zn-propionate were better than inorganic sources such as ZnO or ZnSO4 because they are more bioavailable than inorganic sources.

Conflict of interest

The authors do not have conflict of interest in this work.

Acknowledgements

All the authors of the manuscript thank and acknowledge their respective Universities and Institutes.

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