单胃动物锌代谢及其对营养需要量和饲料锌生物利用率估算的影响

Zn metabolism of monogastric species and consequences for the definition of feeding requirements and the estimation of feed Zn bioavailability 单胃动物锌代谢及其对营养需要量和饲料锌生物利用率估算的影响 corresp first-author ‡Corresponding Author ‡Corresponding Author †E-mail:daniel.brugger@wzw.tum.de †E-mail:daniel.brugger@wzw.tum.de daniel.brugger@wzw.tum.de Chair of Animal Nutrition, TUM School of Life Sciences Weihenstephan, Technical University of Munich, 85354 Freising, Germany Chair of Animal Nutrition, TUM School of Life Sciences Weihenstephan, Technical University of Munich, 85354 Freising, Germany A major goal of mineral nutrition research is to provide information of feed zinc (Zn) utilization efficiency and gross Zn requirements as affected by changing rearing conditions. This can be achieved only by applying precise experimental models that acknowledge the basic principles of Zn metabolism. This review article summarizes the most important aspects of Zn homeostasis in monogastric species, including molecular aspects of Zn acquisition and excretion. Special emphasis is given to the role of the skeleton as well as the exocrine pancreas for animal Zn metabolism. Finally, we discuss consequences arising from these physiological principles for the experimental design of trials which aim to address questions of Zn requirements and bioavailability. (感谢华中农业大学晏向华教授为本文翻译中文概要) Monogastric species Zinc metabolism Requirement Bioavailability Experimental modelling 单胃动物 锌代谢 需要量 生物利用率 实验模型 Introduction 1 Zinc (Zn) is one of the most abundant metals within animals. Reported average tissue concentrations are species-dependent and range from 25 mg/kg (rabbit) to 50 mg/kg (swine) of defatted tissue (Klasing et al., 2005 2005 ). Earlier studies in pigs highlighted total systemic failure of metabolism due to long-term alimentary Zn deficiency, resulting in growth depression, anorexia, tissue necrosis, and other quite unspecific symptoms (Tucker and Salmon, 1955 1955 ). Therefore, it is obvious that its bioactivity is essential for the development and reproduction of animals, which has been confirmed in other models across biological kingdoms (Raulin, 1869 1869 ; Sommer and Lipman, 1926 1926 ; Todd et al., 1934 1934 ; Bertrand and Bhattacherjee, 1935 1935 ; Legg and Sears, 1960 1960 ; O'Dell et al., 1977 1977 ). The importance of Zn in cellular systems is based on its role as a structural and catalytic cofactor of specific peptides. Several Zn motifs in peptides have been described, among which the Zn-finger motifs of certain DNA-binding factors are the most prominent (Pace and Weerapana, 2014 2014 ). Further studies identified a role of free Zn 2+ ions within cells as second messengers as well as activating and repressing agents of peptide activity (Maret, 2013 2013 ; Levaot and Hershfinkel, 2018 2018 ). Andreini et al. ( 2006 2006 ) estimated that about 10% of the human genome codes for Zn-metallo-proteins, most of which have been linked to fundamental processes of cell physiology like transcription, replication, and maintenance of DNA. Hence, it is not surprising that endogenous Zn deficiency may lead to systemic problems resulting in unspecific symptoms. In contrast, Zn excess promotes serious toxic effects. This is also due to its interaction with peptides, but in a rather unspecific and uncontrolled manner (Sandstead, 1995 1995 ). Therefore, evolution gave rise to the formation of a complex and finely-orchestrated homeostatic regulation, which aims to maintain a basal Zn load behind the gut barrier and plasma membrane that benefits metabolic activity under changing environmental conditions (Lichten and Cousins, 2009 2009 ; Colvin et al., 2010 2010 ). Although Zn metabolism has been the subject of intense research for more than a century, still there are a lot of unsolved questions. These involve the identification of the master regulators of systemic Zn homeostatic regulation and the precise chemical principles that affect Zn absorption from food and feed under varying conditions. This review presents the basic principles of Zn metabolism in monogastric organisms. Furthermore, the roles of the skeleton and exocrine pancreas in Zn metabolism are discussed. These concepts should be taken into account in the design of in vivo experiments addressing questions of dietary Zn utilization under varying feeding conditions. Basic principles of Zn metabolism 1 The essential trace elements can be grouped according to the main mechanisms that control their total content within an organism. Whereas iodine and selenium are regulated mainly by renal excretion, the essential transition metals (e.g. Fe, Cu, and Mn) including Zn are regulated by a finely-tuned interplay between luminal absorption from, and endogenous secretion into, the intestines (reviewed by Windisch ( 2002 2002 )). Thereby, Zn homeostasis maintains body Zn at a level that enables proper functioning of metabolic processes. Precise dose-response studies in 65 Zn-labelled rats have highlighted the adaption of absorption and excretion pathways under varying Zn feeding conditions in high resolution. These datasets represent the most important source of current knowledge regarding the status-dependent Zn fluxes through the organism (presented in detail below). Under conditions of insufficient dietary Zn supply, the system starts quite quickly (within the first hour) to mobilize internal Zn stores predominantly from skeletal tissue (Windisch, 2001 2001 , 2003a 2003a ). Within 3–5 d, absorptive and excretive mechanisms also adapt by increasing the relative absorption capacity at the gut barrier and, simultaneously, decreasing endogenous losses into the gut via pancreatic and bile secretions to a minimal amount (Weigand and Kirchgessner, 1980 1980 ; Windisch and Kirchgessner, 1994a 1994a , 1994b 1994b ). This can be considered to represent an attempt to optimize the recycling of luminal Zn, which is represented mainly by endogenous losses under severe Zn malnutrition. The lag time of absorption and excretion directly reflects the half-life of gut mucosal and pancreatic acinar cells (Barker, 2014 2014 ). Because of this delayed response, the first days of Zn deficiency are characterized by the highest endogenous losses (Windisch, 2003a 2003a ). On the other hand, adequate or excessive dietary Zn uptake is associated with reduced Zn absorption efficiency from the intestinal lumen and, at the same time, elimination of excessive Zn levels behind the intestinal barrier by secretion into the gastrointestinal tract (GIT). In this regard, the degree of excretory activity depends on the total amount of Zn in feed. The more Zn is supplemented above the actual requirement, the higher the excretory activity in response (Weigand and Kirchgessner, 1980 1980 ; Windisch and Kirchgessner, 1994a 1994a , 1994b 1994b ). Note that a sudden parenteral application of 65 Zn facilitates excretion primarily via urine not faeces within the first 8 h post-injection (Schwarz and Kirchgessner, 1976 1976 ). Therefore, it seems like the kidney functions as a “first line of defense” to sudden toxic Zn overload. Pieper et al. ( 2015 2015 ) investigated the porcine pancreatic response to excess dietary supplementation with Zn (about 2500 mg/kg). Apart from an accumulation of pancreatic Zn and upregulation of metallothionein, they found higher synthesis of pancreatic digestive enzymes, which points towards higher exogenous pancreatic activity. At first view, the increase in endogenous Zn in response to over-supplementation appears odd considering the aforementioned down-regulation of active absorption pathways at the gut barrier. However, after down-regulation of active transport, there are still passive mechanisms that remain unaffected by Zn homeostatic regulation (Martin et al., 2013 2013 ). Several transport proteins for certain divalent cations express some affinity for a variety of metals, although not to the same degree as their major ligands (Sandström, 2001 2001 ). As soon as the main Zn absorption pathway is down-regulated in response to sufficient or excessive supply, the probability that Zn will compete for different divalent cation transport routes increases. Therefore, the total passively transported amount of Zn strongly correlates with the amount of over-supplemented Zn (Martin et al., 2013 2013 ). Increasing evidence suggests that the response patterns discussed above are due to a sophisticated homeostatic regulation which modulates the biosynthesis, degradation, and translocation of specific Zn transporting proteins within the cells of key tissues. These transporters belong to two main groups of solute carriers (SLC families 30 (ZnT) and 39 (ZIP)). In mammals, 10 members of the ZnT family and 14 members of the ZIP family have been described (Lichten and Cousins, 2009 2009 ; O'Leary et al., 2016 2016 ). It appears that the activities of specific peptides at plasma or vesicular membranes of enterocytes (ZnT1 and ZIP4) and pancreatic acinar cells (ZnT1, ZnT2, and ZIP5) are important factors for the adaption of an organism to changing alimentary Zn supply levels (Lichten and Cousins, 2009 2009 ; Fukada and Kambe, 2011 2011 ; Schweigel-Röntgen, 2014 2014 ). ZIP and ZnT peptides can be distinguished by their transport direction. The ZIP family members transport Zn 2+ from the extracellular space or intracellular compartments towards the cytosol. In contrast, ZnT peptides transport in the opposite direction and decrease cytosolic Zn by transferring it outside of the cell or into vesicles or organelles (Lichten and Cousins, 2009 2009 ; Fukada and Kambe, 2011 2011 ; Schweigel-Röntgen, 2014 2014 ). ZIP4 is abundant in various cell types and tissues including the intestines. It represents the major active apical transport mechanism for luminal Zn 2+ into gut mucosal cells (Wang et al., 2002 2002 ; Dufner-Beattie et al., 2003 2003 , 2007 2007 ; Liuzzi et al., 2004 2004 ). Data from several labs suggest that intestinal ZIP4 activity is modulated by transcriptional and post-transcriptional processes. Dietary Zn deficiency promotes increased synthesis and presentation of the peptide at the apical plasma membrane. In contrast, repletion of body Zn stores initiates ZIP4 endocytosis and ubiquitination as well as messenger RNA (mRNA) degradation (Mao et al., 2007 2007 ; Weaver et al., 2007 2007 ; Kambe and Andrews, 2009 2009 ). It has been further demonstrated that ZIP4 mRNA counts are a product of varying mRNA stability and kruppel-like-factor 4 (KLF4) activity (Liuzzi et al., 2009 2009 ; Curry-McCoy et al., 2013 2013 ). In contrast to ZIP4, intestinal ZnT1 activity involves the basolateral transfer of cytosolic Zn 2+ into the circulation (McMahon and Cousins, 1998 1998 ; Cousins and McMahon, 2000 2000 ; Liuzzi et al., 2001 2001 ; Andrews et al., 2004 2004 ). Its interplay with ZIP4 activity represents the dominant apical-to-basolateral uptake route for dietary Zn into the organism. Earlier data suggest that free cytosolic Zn 2+ is the major regulative stimulus of ZnT1 by activating metal responsive transcription factor 1 (MTF1) (Brugnera et al., 1994 1994 ; Langmade et al., 2000 2000 ; Liuzzi et al., 2001 2001 ). Hence, it is not the overall body Zn status that affects ZnT1 activity, but fluctuations of free cytosolic Zn 2+ as affected by different Zn transporters. A major proportion of the endogenous Zn that is excreted into the GIT is of pancreatic origin (Oberleas, 1996 1996 ; Holt et al., 2012 2012 ). This highlights the essential role of the pancreas in Zn metabolism. Zn excretion into the intestine via the pancreatic duct occurs predominantly by exocytosis of Zn metallopeptides rather than free Zn 2+ (Matsuno et al., 1982 1982 ). This includes, for example, the pancreatic carboxypeptidases A and B, which need Zn 2+ to bind their catalytic centre (Folk et al., 1960 1960 ; Folk and Schirmer, 1963 1963 ; Hsu et al., 1966 1966 ; Mills et al., 1967 1967 ; Roth and Kirchgessner, 1974 1974 ). The transporter ZnT2 has been identified as responsible for loading cytosolic Zn into vesicles of pancreatic acinar cells. It shows a reduced abundance during Zn deficiency, which has been associated with a marked decrease of the Zn concentration within pancreatic zymogen granules. On the other hand, Zn overload promotes the opposite response (Guo et al., 2010 2010 ). Zn deficiency has also been associated with higher ZnT1 activity at pancreatic basolateral membranes (Liuzzi et al., 2004 2004 ). This indicates a rerouting of pancreatic Zn into the circulation for the benefit of other tissues during Zn deficiency. In contrast, increased pancreatic Zn absorption from the circulation under Zn-replete conditions is due to basolateral ZIP5 activity, which is evident in many tissues and cell types including pancreatic acinar cells (Dufner-Beattie et al., 2004 2004 ). Zn deficiency, however, promotes degradation of pancreatic ZIP5 and associated reduction in absorption of circulatory Zn. Weaver et al. ( 2007 2007 ) suggest that ZIP5 abundance is regulated at the translational rather than the transcriptomic level. They demonstrated that ZIP5 mRNA is continuously located at polysomes where it can be quickly translated if necessary. However, our data obtained in the gut mucosa of piglets highlight a regulation of pancreatic ZIP5 gene expression in response to the dietary Zn supply during short-term subclinical Zn deficiency (Brugger, 2018 2018 ). There are currently 24 Zn transporters described in mammals. Furthermore, a whole set of other factors affecting intracellular Zn trafficking and exchange has been identified. Presenting the current knowledge about all currently known molecular key players in Zn homeostasis would exceed this manuscript’s capacity. Fortunately, a set of excellent reviews has been published, which address the molecular biology and biochemistry of Zn metabolism in more detail (Lichten and Cousins, 2009 2009 ; Colvin et al., 2010 2010 ; Fukada and Kambe, 2011 2011 ; Schweigel-Röntgen, 2014 2014 ). Role of the skeleton as a reservoir for mobilizable Zn 1 Weaned piglets develop the first signs of clinical Zn deficiency (feed refusal) after approximately 10 d of low Zn intake (Windisch, 2003b 2003b ; Ettle et al., 2005 2005 ). To compensate for the negative side-effects of malnutrition for several days, the body must contain some kinds of Zn storage compartment. Some soft tissues like the liver can accumulate Zn, but these sinks are limited and therefore become exhausted quite quickly (Windisch, 2003a 2003a ). Precise metabolism trials with 65 Zn-labelled rats have demonstrated the central role of the skeleton as a source of mobilizable Zn during times of deficiency. These datasets indicate that under conditions of dietary Zn deficiency, mobilization of stored Zn occurs primarily from the skeleton (Windisch, 2001 2001 , 2003a 2003a ). Furthermore, during subsequent repletion, bone Zn stores undergo a quick and targeted refilling until the original level is replenished (Windisch, 2001 2001 ). This quick repletion is due to the above described higher ZIP4 activity on the apical gut mucosa of depleted individuals. Interestingly, trabecular bone tissue in particular is involved in Zn exchange mechanisms (Windisch et al., 2002 2002 ), which is why such bone material (e.g. the femoral head) should be used to monitor the status of Zn storage in studies on Zn metabolism trials. The mobilization and storage of Zn in bone tissue appear to happen independently from general mechanisms of bone turnover, which may point towards a distinct, passive process (Windisch et al., 2002 2002 ; Brugger et al., 2018 2018 ). This is in line with data from pigs that show a strong linear correlation between bone Zn and plasma Zn (steady state) in response to different dietary Zn concentrations (Brugger et al., 2014 2014 ). In recent years, the opinion has prevailed that bone Zn mobilization is a rather slow process and that for a quick response the soft tissue compartments are more important. However, this contradicts the experimental data which clearly demonstrate that bone Zn mobilization happens within the first 24 h of deficient supply (Windisch, 2003a 2003a ). Interestingly, our data highlight changes in bone Zn within only 1 h post feeding (Brugger et al., 2018 2018 ). This adaption is quicker than the changes in absorptive capacity and endogenous secretion at the gut barrier, which need 3–5 d to fully adapt. Hence, bone Zn reservoirs appear to be highly mobile. As soon as the mobilizable fraction of bone Zn is completely exhausted, clinical symptoms arise (Windisch, 2003b 2003b ). The precise mechanisms of Zn exchange between the blood and skeleton as well as their interactions with bone tissue remain unclear and must be subject to further research. Interaction of exogenous pancreatic activity and Zn metabolism 1 The adaption of pancreatic Zn excretory behavior points towards a direct interaction between Zn supply and digestive capacity. Indeed, the exogenous pancreas is necessary for providing sufficient digestive capacity to the organism as it is responsible for the production and excretion of a large proportion of necessary digestive enzymes, especially proteases. These include trypsin, chymotrypsin, carboxypeptidases A and B, elastase, α-amylase, and pancreatic lipase (Klein, 2019 2019 ). An impairment of pancreatic metabolism, e.g. in the course of pathological events like pancreatitis, is therefore associated with impaired digestive function (Lankisch et al., 2015 2015 ). This may also account for fluctuations in the supply status of nutrients, especially those that, like Zn, are regulated by pancreatic activity. Earlier studies detected signs of severe digestive depression as a result of clinical Zn deficiency. One of the most illustrative examples is the classic study of Tucker and Salmon ( 1955 1955 ). They demonstrated for the first time that Zn was essential for growing pigs. They noticed severe cases of diarrhea and anorexia of pigs being fed with cereal-based diets without Zn fortification. All symptoms could be cured by generous addition (up to 2% on top of the basal diet) of ZnCO 3 . Other studies reached similar conclusions in other models (Raulin, 1869 1869 ; Sommer and Lipman, 1926 1926 ; Todd et al., 1934 1934 ; Bertrand and Bhattacherjee, 1935 1935 ; Legg and Sears, 1960 1960 ; O'Dell et al., 1977 1977 ). By controlling for bias due to changes in feed intake behavior, Roth et al. ( 1992 1992 ) recognized a significant drop in digestive capacity of clinically Zn-deficient force-fed rats. This was a first hint that growth depression in response to Zn deficiency is due only in part to anorexia. Our data, obtained from restrictively fed subclinical Zn-deficient piglets, confirmed these findings and further highlighted a reduced synthesis of exogenous digestive enzymes within Zn-depleted pancreatic tissue (Brugger and Windisch, 2016a 2016a , 2016b 2016b ). Under conditions of excess Zn supplementation (e.g. when applying pharmacological Zn dosages (about 2500 mg Zn/kg diet)), the response appears to be shifted to the opposite (Pieper et al., 2015 2015 ). This group also found a higher abundance of exogenous digestive enzymes and Zn in pancreatic tissue of piglets excessively supplemented with Zn. Hence, exogenous pancreatic excretion of Zn may be functionally related to the excretion of pancreatic digestive enzymes. Some of these enzymes (carboxypeptidases) are Zn metalloenzymes (Folk et al., 1960 1960 ; Folk and Schirmer, 1963 1963 ; Hsu et al., 1966 1966 ). It appears plausible that Zn is not excreted as free Zn 2+ ions considering their strong toxic potential (Bozym et al., 2010 2010 ). Also, the finding that not only carboxypeptidases but the whole set of pancreatic digestive enzymes is affected during Zn deficiency and excess (Brugger and Windisch, 2016a 2016a , 2016b 2016b ), suggests that the excretion of pancreatic enzymes is not enzyme-specific, but rather involves the complete set of catalytic peptides. A higher necessity for peptide synthesis in times of Zn excess may in part explain the higher abundance of stress peptides in the course of pancreatic Zn accumulation (Pieper et al., 2015 2015 ). In summary, the organism is entering a “vicious circle” in the course of Zn deficiency. On the one hand, it must avoid losing too much Zn into the GIT through exogenous pancreatic secretion. On the other hand, the consequent reduction of digestive capacity increases the Zn supply problem, as digestive breakdown of the feed matrix is crucial for the absorption of all nutrients, including Zn. Consequences for the definition of requirements and the estimation of bioavailability 1 The aforementioned principles of Zn homeostasis should be considered when planning experiments that aim to define Zn feeding requirements and recommendations. The magnitude of body Zn depletion determines the intensity by which a status parameter responds to dietary treatment. In several studies, a higher intestinal ZIP4 activity and transcription were observed in Zn-deficient individuals than in control groups. The response appears to be even more pronounced when comparing clinically to subclinically Zn-deficient individuals (Dufner-Beattie et al., 2003 2003 , 2004 2004 ; Brugger, 2018 2018 ). Indeed, an organism which is so severely depleted with Zn that obvious degenerative processes occur must temporarily acquire more Zn from the GIT lumen to refill its emptied stores and, simultaneously, supply Zn for processes of maintenance and regeneration (Prasad, 1985 1985 ). However, such severe events of Zn deficiency are very rare in nature, especially under the terms of practical livestock production (Caulfield and Black, 2004 2004 ). Therefore, Zn feeding thresholds which have been defined based on studies in clinically Zn-deficient animals are less relevant from a practical point of view. In addition, in these studies comparisons are made between healthy and sick individuals, which further reduces their informative value. In contrast, subclinical Zn deficiencies are more likely to occur in livestock farms (Nielsen, 2012 2012 ), for example during periods of temporarily reduced feed intake (e.g. in the weanling phase, as described by Lallés et al. ( 2007 2007 )). Therefore, it seems more appropriate to model this specific physiological state in experiments aimed at providing recommendations for practical Zn feeding. Usually, the term bioavailability is predominantly used as a synonym for absorbability. Although this may be suitable in regard to certain substances, it is not appropriate for Zn. Its solubility kinetics during the gastrointestinal passage is a rather poor indicator of its absorption rate. If this was not so, solubility indices would already be used in practical feeding to predict Zn feeding efficacy under varying dietary conditions. This lack of correlation is evidently explained by the previously discussed metabolic processes as a function of the status of the body’s Zn reserves. Rather than aiming to identify or develop Zn sources with peak solubility values, we should be seeking those that satisfy metabolic demands with the lowest possible dietary Zn concentration under practical conditions. This obviously applies also to other nutrients and nutritive elements. Therefore, for an animal nutritionist the estimation of relative bioavailability is tightly connected to the measurement of gross requirements. In the end, we do not investigate the solubility kinetics of Zn sources, but their efficiency in mediating Zn 2+ transfer to the mucosal transport peptides. To assess Zn bioavailability and requirements, the response of appropriate status parameters in standardized high-resolution dose-response studies must be observed. It is of utmost importance to choose the range of applied dosages in a way that allows discrimination between Zn-deficient and sufficiently supplied animals. Furthermore, these dosages should cover the range from potentially deficient to sufficient supply levels in high resolution, to allow a mapping of the gross Zn requirement threshold. The state-of-the-art approach is to use linear and non-linear regression models to estimate dietary thresholds, below or above which significant differences are evident in the response behavior of suitable status parameters to varying Zn supply (Robbins et al., 2006 2006 ). These “breakpoints” may mark the minimum dosage to satisfy the gross Zn requirement. However, the question remains, what is a “suitable status parameter”? On the one hand, it must express a highly significant responsiveness to varying dietary Zn supply. On the other hand, the intensity or direction of the response should change when the dietary Zn intake falls below, meets, or exceeds the gross requirement. Apart from its relationship to changes in body Zn status, a Zn status parameter should also meet some functional prerequisites. Zn is important for basic mechanisms in all cell types. Hence, a lot of parameters would respond to a change in the Zn supply status, including some not directly related to Zn homeostatic regulation. Prominent examples involve key players of redox metabolism and immune function (reviewed by Eide ( 2011 2011 ) and Haase and Rink ( 2014 2014 )). Indeed, parameters related to these metabolic pathways have been shown to be affected by Zn homeostatic regulation (Brugger and Windisch, 2017a 2017a ; Kloubert et al., 2018 2018 ). However, this also implies that under more practical experimental conditions, environmental stressors like infections might bias the results. Furthermore, some data suggest that certain parameters of Zn homeostasis respond less to the body Zn status itself, but more to the stress or inflammatory status of a tissue (Brugger, 2018 2018 ). Hence, monitoring these factors to highlight homeostatic regulation in the context of body Zn losses appears questionable. A preferable parameter to estimate Zn requirements or availability should reflect Zn homeostatic regulation in relation to changes in body Zn. Based on our experience, the apparent digestion of dietary Zn has proved to be a robust indicator of the status of Zn homeostatic regulation (Brugger et al., 2014 2014 ). Earlier studies clearly demonstrated it to be highly and significantly correlated with the truly absorbed dietary Zn (Weigand and Kirchgessner, 1980 1980 ; Windisch and Kirchgessner, 1999 1999 ). Hence, this parameter directly reflects the Zn homeostatic regulation at the gut barrier, which plateaus over sufficiently supplied groups. This allows a differentiation between animals fed diets with insufficient or sufficient Zn concentrations under experimental conditions. Furthermore, it can be measured in vivo without killing animals, as only feed and fecal samples are needed. The sole use of partial digestibility data (e.g. from the end of the ileum) would not be sufficient, as it has been shown that the colon absorbs significant amounts of luminal Zn and its ZIP4 gene expression is regulated depending on the Zn supply status (Hara et al., 2000 2000 ; Brugger, 2018 2018 ). Consequently, ignoring the quantitative role of the colon in Zn absorption inevitably leads to information being lost and the data quality of studies on Zn metabolism being impaired (for a more comprehensive discussion on suitable status parameters, see Brugger et al. ( 2014 2014 )). The chemical conformation in the intestinal lumen, together with the physiological status of the animal, determines the net amount of ingested feed Zn. The former is a product of the chemical ligands associated with Zn (chemical Zn species) under luminal conditions, and the extent and diversity of their interactions with other feed components and endogenously excreted substances (Windisch, 2002 2002 ). Active Zn transporters accomplish Zn transfer through biological membranes exclusively with divalent cations (Zn 2+ ) (reviewed by Holt et al. ( 2012 2012 ), Lichten and Cousins ( 2009 2009 ), and Schweigel-Röntgen ( 2014 2014 )). Therefore, the absorption of luminal Zn depends on the total content of free Zn 2+ ions (usually very low) and above all on the amount of Zn loosely bound to respective chemical ligands (Windisch, 2002 2002 ). Significant levels of luminal Zn appear to be unavailable in practical swine diets due to their association with phytic acid in the course of gastrointestinal passage (Cosgrove, 1980 1980 ). Therefore, growing piglets without appropriate Zn supply from complete feed develop clinical Zn deficiency within about 10 d (Windisch, 2003b 2003b ; Ettle et al., 2005 2005 ). Previous data indicate the gross Zn requirement of weanling piglets at 50‒60 mg/kg in modern high phytate diets without addition of exogenous phytase (Lewis et al., 1956 1956 , 1957a 1957a , 1957b 1957b ; Luecke et al., 1956 1956 ; Stevenson and Earle, 1956 1956 ; Smith et al., 1958 1958 , 1962 1962 ; Shanklin et al., 1968 1968 ; Liptrap et al., 1970 1970 ; Brugger et al., 2014 2014 ). Assuming Zn requirements of 15–20 mg/kg under semi-synthetic dietary conditions without phytic acid (Smith et al., 1962 1962 ; Shanklin et al., 1968 1968 ) and native Zn levels of cereal-based diets of 30–40 mg/kg (Brugger et al., 2014 2014 ), we conclude in context to the defined requirements (about 50 mg/kg) of growing piglets (Lewis et al., 1956 1956 , 1957a 1957a , 1957b 1957b ; Luecke et al., 1956 1956 ; Stevenson and Earle, 1956 1956 ; Smith et al., 1958 1958 , 1962 1962 ; Shanklin et al., 1968 1968 ; Liptrap et al., 1970 1970 ; Brugger et al., 2014 2014 ) that in practical feeding systems a high proportion of supplemented Zn is needed to saturate phytic acid Zn-binding sites, rather than the actual net requirement. Therefore, the essence of Zn supplementation strategies for pigs and poultry is to increase the total amount of luminal Zn to provide an excess of non-phytate Zn that can meet the body’s Zn requirements. Not only does this underscore the need for elevated dietary levels of Zn in the presence of phytate-rich diets, but it also suggests the ideal range of dietary Zn doses intended for dose-response studies to modulate Zn metabolism. These should cover deficient ( < 50 mg/kg diet) and adequate intake levels (≥50 mg/kg diet) to reflect the dose-dependent adaptation of Zn homeostasis, which allows estimation of the respective Zn requirement threshold. Conclusions and outlook 1 A crucial cornerstone for more sustainability in animal nutrition is to establish precision feeding. This applies especially to micromineral supplementation. Indeed, high-yielding livestock animals must be supplied with sufficient amounts to maintain productivity and wellbeing through all stages of the production cycle. However, excessive supplementation far above the requirement thresholds should be avoided as this has been associated with environmental concerns as well as impaired animal and human health (reviewed for Zn in more detail by Brugger and Windisch ( 2015 2015 ) and Brugger and Windisch ( 2017b 2017b )). European authorities recently acknowledged these issues by decreasing allowed upper limits for total Zn concentrations in feed (The European Commission, 2016 2016 ). However, the allowed maximum of 150 mg/kg for piglets is still about three times their requirement (about 50 mg/kg diet) (Lewis et al., 1956 1956 , 1957a 1957a , 1957b 1957b ; Luecke et al., 1956 1956 ; Stevenson and Earle, 1956 1956 ; Smith et al., 1958 1958 , 1962 1962 ; Shanklin et al., 1968 1968 ; Liptrap et al., 1970 1970 ; Brugger et al., 2014 2014 ). This generosity in terms of safety margins reflects uncertainty regarding the magnitude of Zn utilization as well as the parameters that affect it under practical conditions. To refine current Zn feeding recommendations, there is a set of research questions that first have to be answered. There is an urgent need for studies comprising modern genotypes highlighting the changes in Zn requirements under changing dietary and environmental conditions. This must be done by applying appropriate and precise experimental models, the cornerstones of which have been described above. For weaned piglets such a model is already available (Brugger et al., 2014 2014 ), but for further species they are yet to be developed. Furthermore, we still lack a comprehensive understanding of Zn chemistry along the GIT. Closing this gap is crucial to facilitate a targeted development of efficient Zn supplements for dietary intervention. Therefore, state-of-the-art analytical methods of metal speciation analysis (“metallomics”) must be implemented in mineral nutrition research (Michalke, 2016 2016 ). Furthermore, there is no solid diagnostic marker that indicates the Zn status of an individual with sufficient sensitivity under field conditions (especially in the case of subclinical events). This reflects our limited understanding of the body’s regulation of Zn metabolism, and especially of the molecular transmitters and receivers of information on the body’s Zn supply status in and between tissues. Hence, more basic research on the function of vertebrate Zn homeostasis should be conducted. References C Andreini , L Banci , I Bertini , 等 . Counting the zinc-proteins encoded in the human genome . J Proteome Res , 2006 . 5 ( 1 ): 196 - 201 . 16396512 DOI: 10.1021/pr050361j http://doi.org/10.1021/pr050361j . Counting the zinc-proteins encoded in the human genome GK Andrews , HB Wang , SK Dey , 等 . Mouse zinc transporter 1 gene provides an essential function during early embryonic development . Genesis , 2004 . 40 ( 2 ): 74 - 81 . 15452870 DOI: 10.1002/gene.20067 http://doi.org/10.1002/gene.20067 . Mouse zinc transporter 1 gene provides an essential function during early embryonic development N Barker . Adult intestinal stem cells: critical drivers of epithelial homeostasis and regeneration . Nat Rev Mol Cell Biol , 2014 . 15 ( 1 ): 19 - 33 . 24326621 DOI: 10.1038/nrm3721 http://doi.org/10.1038/nrm3721 . Adult intestinal stem cells: critical drivers of epithelial homeostasis and regeneration G Bertrand , RC Bhattacherjee . Recherches sur l'action combineé du zinc et des vitamins dés l'alimentation des animaux . Bull Soc Sci Hyg Aliment Ration Homme , 1935 . 23 369 - 376 . (in French) . Recherches sur l'action combineé du zinc et des vitamins dés l'alimentation des animaux RA Bozym , F Chimienti , LJ Giblin , 等 . Free zinc ions outside a narrow concentration range are toxic to a variety of cells in vitro . Exp Biol Med , 2010 . 235 ( 6 ): 741 - 750 . DOI: 10.1258/ebm.2010.009258 http://doi.org/10.1258/ebm.2010.009258 . Free zinc ions outside a narrow concentration range are toxic to a variety of cells in vitro D Brugger . Experimental Modelling of Subclinical Zinc Deficiency in Weaned Piglets. PhD D , 2018 . Technical University of Munich, Freising, Germany , 171 - 208 . . Experimental Modelling of Subclinical Zinc Deficiency in Weaned Piglets. PhD D D Brugger , WM Windisch . Environmental responsibilities of livestock feeding using trace mineral supplements . Anim Nutr , 2015 . 1 ( 3 ): 113 - 118 . 29767146 DOI: 10.1016/j.aninu.2015.08.005 http://doi.org/10.1016/j.aninu.2015.08.005 . Environmental responsibilities of livestock feeding using trace mineral supplements D Brugger , W Windisch . Subclinical zinc deficiency impairs pancreatic digestive enzyme activity and digestive capacity of weaned piglets . Br J Nutr , 2016 . 116 ( 3 ): 425 - 433 . 27230230 DOI: 10.1017/S0007114516002105 http://doi.org/10.1017/S0007114516002105 . Subclinical zinc deficiency impairs pancreatic digestive enzyme activity and digestive capacity of weaned piglets D Brugger , W Windisch . Subclinical zinc deficiency impairs pancreatic digestive enzyme activity and digestive capacity of weaned piglets–CORRIGENDUM . Br J Nutr , 2016 . 116 ( 5 ): 950 - 951 . 27374386 DOI: 10.1017/S0007114516002683 http://doi.org/10.1017/S0007114516002683 . Subclinical zinc deficiency impairs pancreatic digestive enzyme activity and digestive capacity of weaned piglets–CORRIGENDUM D Brugger , WM Windisch . Short-term subclinical zinc deficiency in weaned piglets affects cardiac redox metabolism and zinc concentration . J Nutr , 2017 . 147 ( 4 ): 521 - 527 . 28202635 DOI: 10.3945/jn.116.240804 http://doi.org/10.3945/jn.116.240804 . Short-term subclinical zinc deficiency in weaned piglets affects cardiac redox metabolism and zinc concentration D Brugger , WM Windisch . Strategies and challenges to increase the precision in feeding zinc to monogastric livestock . Anim Nutr , 2017 . 3 ( 2 ): 103 - 108 . 29767077 DOI: 10.1016/j.aninu.2017.03.002 http://doi.org/10.1016/j.aninu.2017.03.002 . Strategies and challenges to increase the precision in feeding zinc to monogastric livestock D Brugger , M Buffler , W Windisch . Development of an experimental model to assess the bioavailability of zinc in practical piglet diets . Arch Anim Nutr , 2014 . 68 ( 2 ): 73 - 92 . 24646148 DOI: 10.1080/1745039X.2014.898392 http://doi.org/10.1080/1745039X.2014.898392 . Development of an experimental model to assess the bioavailability of zinc in practical piglet diets D Brugger , M Schlattl , W Windisch . Short-term kinetics of tissue zinc exchange in 65 Zn-labelled adult rats receiving sufficient dietary zinc supply . Proc Soc Nutr Physiol , 2018 . Short-term kinetics of tissue zinc exchange in 65Zn-labelled adult rats receiving sufficient dietary zinc supply E Brugnera , O Georgiev , F Radtke , 等 . Cloning, chromosomal mapping and characterization of the human metal-regulatory transcription factor MTF-1 . Nucleic Acids Res , 1994 . 22 ( 15 ): 3167 - 3173 . 8065932 DOI: 10.1093/nar/22.15.3167 http://doi.org/10.1093/nar/22.15.3167 . Cloning, chromosomal mapping and characterization of the human metal-regulatory transcription factor MTF-1 LE Caulfield , RE Black . Lopez AD Ezzati M , et al Rodgers A . Zinc deficiency . Comparative Quantification of Health Risks: Global and Regional Burden of Disease Attributable to Selected Major Risk Factors , 2004 . World Health Organization, Geneva, Switzerland , . Zinc deficiency RA Colvin , WR Holmes , CP Fontaine , 等 . Cytosolic zinc buffering and muffling: their role in intracellular zinc homeostasis . Metallomics , 2010 . 2 ( 5 ): 306 - 317 . 21069178 DOI: 10.1039/B926662C http://doi.org/10.1039/B926662C . Cytosolic zinc buffering and muffling: their role in intracellular zinc homeostasis DJ Cosgrove . Inositol Phosphates: Their Chemistry, Biochemistry and Physiology , 1980 . Elsevier Scientific Publication, Amsterdam , . Inositol Phosphates: Their Chemistry, Biochemistry and Physiology RJ Cousins , RJ McMahon . Integrative aspects of zinc transporters . J Nutr , 2000 . 130 ( 5 ): 1384S - 1387S . 10801948 DOI: 10.1093/jn/130.5.1384S http://doi.org/10.1093/jn/130.5.1384S . Integrative aspects of zinc transporters TV Curry-McCoy , DM Guidot , PC Joshi . Chronic alcohol ingestion in rats decreases Krüppel-like factor 4 expression and intracellular zinc in the lung . Alcohol Clin Exp Res , 2013 . 37 ( 3 ): 361 - 371 . 23013362 DOI: 10.1111/j.1530-0277.2012.01946.x http://doi.org/10.1111/j.1530-0277.2012.01946.x . Chronic alcohol ingestion in rats decreases Krüppel-like factor 4 expression and intracellular zinc in the lung J Dufner-Beattie , FD Wang , YM Kuo , 等 . The acrodermatitis enteropathica gene ZIP4 encodes a tissue-specific, zinc-regulated zinc transporter in mice . J Biol Chem , 2003 . 278 ( 35 ): 33474 - 33481 . 12801924 DOI: 10.1074/jbc.M305000200 http://doi.org/10.1074/jbc.M305000200 . The acrodermatitis enteropathica gene ZIP4 encodes a tissue-specific, zinc-regulated zinc transporter in mice J Dufner-Beattie , YM Kuo , J Gitschier , 等 . The adaptive response to dietary zinc in mice involves the differential cellular localization and zinc regulation of the zinc transporters ZIP4 and ZIP5 . J Biol Chem , 2004 . 279 ( 47 ): 49082 - 49090 . 15358787 DOI: 10.1074/jbc.M409962200 http://doi.org/10.1074/jbc.M409962200 . The adaptive response to dietary zinc in mice involves the differential cellular localization and zinc regulation of the zinc transporters ZIP4 and ZIP5 J Dufner-Beattie , BP Weaver , J Geiser , 等 . The mouse acrodermatitis enteropathica gene Slc39a4 ( Zip4 ) is essential for early development and heterozygosity causes hypersensitivity to zinc deficiency . Hum Mol Genet , 2007 . 16 ( 12 ): 1391 - 1399 . 17483098 DOI: 10.1093/hmg/ddm088 http://doi.org/10.1093/hmg/ddm088 . The mouse acrodermatitis enteropathica gene Slc39a4 (Zip4) is essential for early development and heterozygosity causes hypersensitivity to zinc deficiency DJ Eide . The oxidative stress of zinc deficiency . Metallomics , 2011 . 3 ( 11 ): 1124 - 1129 . 21789324 DOI: 10.1039/C1MT00064K http://doi.org/10.1039/C1MT00064K . The oxidative stress of zinc deficiency T Ettle , W Windisch , FX Roth . Strain JJ . The effect of phytase on the bioavailability of zinc in piglets . TEMA 12: 12th International Symposium on Trace Elements in Man and Animals , 2005 . University of Ulster, Coleraine, Northern Ireland, UK , 55 . The effect of phytase on the bioavailability of zinc in piglets Commission The European . Commission Implementing regulation (EU) 2016/1095 of 6 July 2016 concerning the authorisation of Zinc acetate dihydrate, Zinc chloride anhydrous, Zinc oxide, Zinc sulphate heptahydrate, Zinc sulphate monohydrate, Zinc chelate of amino acids hydrate, Zinc chelate of protein hydrolysates, Zinc chelate of glycine hydrate (solid) and Zinc chelate of glycine hydrate (liquid) as feed additives for all animal species and amending Regulations (EC) No 1334/2003, (EC) No 479/2006, (EU) No 335/2010 and Implementing Regulations (EU) No 991/2012 and (EU) No 636/2013 . Official J Eur Union , 2016 . 182 7 - 27 . . Commission Implementing regulation (EU) 2016/1095 of 6 July 2016 concerning the authorisation of Zinc acetate dihydrate, Zinc chloride anhydrous, Zinc oxide, Zinc sulphate heptahydrate, Zinc sulphate monohydrate, Zinc chelate of amino acids hydrate, Zinc chelate of protein hydrolysates, Zinc chelate of glycine hydrate (solid) and Zinc chelate of glycine hydrate (liquid) as feed additives for all animal species and amending Regulations (EC) No 1334/2003, (EC) No 479/2006, (EU) No 335/2010 and Implementing Regulations (EU) No 991/2012 and (EU) No 636/2013 JE Folk , EW Schirmer . The porcine pancreatic carboxypeptidase A system. I. Three forms of the active enzyme . J Biol Chem , 1963 . 238 ( 12 ): 3884 - 3894 . 14086721 . The porcine pancreatic carboxypeptidase A system. I. Three forms of the active enzyme JE Folk , KA Piez , WR Carroll , 等 . Carboxy-peptidase B. 4. Purification and characterization of the porcine enzyme . J Biol Chem , 1960 . 235 ( 8 ): 2272 - 2277 . 13823740 . Carboxy-peptidase B. 4. Purification and characterization of the porcine enzyme T Fukada , T Kambe . Molecular and genetic features of zinc transporters in physiology and pathogenesis . Metallomics , 2011 . 3 ( 7 ): 662 - 674 . 21566827 DOI: 10.1039/C1MT00011J http://doi.org/10.1039/C1MT00011J . Molecular and genetic features of zinc transporters in physiology and pathogenesis L Guo , LA Lichten , MS Ryu , 等 . STAT5-glucocorticoid receptor interaction and MTF-1 regulate the expression of ZnT2 (Slc30a2) in pancreatic acinar cells . Proc Natl Acad Sci USA , 2010 . 107 ( 7 ): 2818 - 2823 . DOI: 10.1073/pnas.0914941107 http://doi.org/10.1073/pnas.0914941107 . STAT5-glucocorticoid receptor interaction and MTF-1 regulate the expression of ZnT2 (Slc30a2) in pancreatic acinar cells H Haase , L Rink . Multiple impacts of zinc on immune function . Metallomics , 2014 . 6 ( 7 ): 1175 - 1180 . 24531756 DOI: 10.1039/c3mt00353a http://doi.org/10.1039/c3mt00353a . Multiple impacts of zinc on immune function H Hara , A Konishi , T Kasai . Contribution of the cecum and colon to zinc absorption in rats . J Nutr , 2000 . 130 ( 1 ): 83 - 89 . 10613771 DOI: 10.1093/jn/130.1.83 http://doi.org/10.1093/jn/130.1.83 . Contribution of the cecum and colon to zinc absorption in rats RR Holt , JY Uiu-Adams , CL Keen . Macdonald IA Erdman JW , Zeisel SH . Zinc . Present Knowledge in Nutrition , 2012 . Wiley-Blackwell, Hoboken, New Jersey , 521 - 539 . . Zinc JM Hsu , JK Anilane , DE Scanlan . Pancreatic carboxypeptidases: activities in zinc deficient rats . Science , 1966 . 153 ( 3738 ): 882 - 883 . 5914752 DOI: 10.1126/science.153.3738.882 http://doi.org/10.1126/science.153.3738.882 . Pancreatic carboxypeptidases: activities in zinc deficient rats T Kambe , GK Andrews . Novel proteolytic processing of the ectodomain of the zinc transporter ZIP4 (SLC39A4) during zinc deficiency is inhibited by acrodermatitis enteropathica mutations . Mol Cell Biol , 2009 . 29 ( 1 ): 129 - 139 . 18936158 DOI: 10.1128/MCB.00963-08 http://doi.org/10.1128/MCB.00963-08 . Novel proteolytic processing of the ectodomain of the zinc transporter ZIP4 (SLC39A4) during zinc deficiency is inhibited by acrodermatitis enteropathica mutations KC Klasing , JP Goff , JL Greger , 等 . National Research Council . Zinc . Mineral Tolerance of Animals , 2005 . The National Academies Press, Washington, DC, USA , 413 - 427 . . Zinc BG Klein . Cunningham’s Textbook of Veterinary Physiology, 6th Ed , 2019 . Elsevier, St. Louis, Missouri, USA , 307 - 315 . . Cunningham’s Textbook of Veterinary Physiology, 6th Ed V Kloubert , K Blaabjerg , TS Dalgaard , 等 . Influence of zinc supplementation on immune parameters in weaned pigs . J Trace Elem Med Biol , 2018 . 49 231 - 240 . 29402502 DOI: 10.1016/j.jtemb.2018.01.006 http://doi.org/10.1016/j.jtemb.2018.01.006 . Influence of zinc supplementation on immune parameters in weaned pigs JP Lallés , P Bosi , H Smidt , 等 . Nutritional management of gut health in pigs around weaning . Proc Nutr Soc , 2007 . 66 ( 2 ): 260 - 268 . DOI: 10.1017/S0029665107005484 http://doi.org/10.1017/S0029665107005484 . Nutritional management of gut health in pigs around weaning SJ Langmade , R Ravindra , PJ Daniels , 等 . The transcription factor MTF-1 mediates metal regulation of the mouse ZnT1 gene . J Biol Chem , 2000 . 275 ( 44 ): 34803 - 34809 . 10952993 DOI: 10.1074/jbc.M007339200 http://doi.org/10.1074/jbc.M007339200 . The transcription factor MTF-1 mediates metal regulation of the mouse ZnT1 gene PG Lankisch , M Apte , PA Banks . Acute pancreatitis . Lancet , 2015 . 386 ( 9988 ): 85 - 96 . 25616312 DOI: 10.1016/S0140-6736(14)60649-8 http://doi.org/10.1016/S0140-6736(14)60649-8 . Acute pancreatitis SP Legg , L Sears . Zinc sulphate treatment of parakeratosis in cattle . Nature , 1960 . 186 ( 4730 ): 1061 - 1062 . 14415314 DOI: 10.1038/1861061a0 http://doi.org/10.1038/1861061a0 . Zinc sulphate treatment of parakeratosis in cattle N Levaot , M Hershfinkel . How cellular Zn 2+ signaling drives physiological functions . Cell Calcium , 2018 . 75 53 - 63 . 30145429 DOI: 10.1016/j.ceca.2018.08.004 http://doi.org/10.1016/j.ceca.2018.08.004 . How cellular Zn2+ signaling drives physiological functions PK Lewis , WG Hoekstra , RH Grummer , 等 . The effect of certain nutritional factors including calcium, phosphorus and zinc on parakeratosis . J Anim Sci , 1956 . 15 ( 3 ): 741 - 751 . DOI: 10.2527/jas1956.153741x http://doi.org/10.2527/jas1956.153741x . The effect of certain nutritional factors including calcium, phosphorus and zinc on parakeratosis PK Lewis , WG Hoekstra , RH Grummer . Restricted calcium feeding versus zinc supplementation for the control of parakeratosis in swine . J Anim Sci , 1957 . 16 ( 3 ): 578 - 588 . DOI: 10.1093/ansci/16.3.578 http://doi.org/10.1093/ansci/16.3.578 . Restricted calcium feeding versus zinc supplementation for the control of parakeratosis in swine PK Lewis , RH Grummer , WC Hoekstra . The effect of method of feeding upon the susceptibility of the pig to parakeratosis . J Anim Sci , 1957 . 16 ( 4 ): 927 - 936 . DOI: 10.2527/jas1957.164927x http://doi.org/10.2527/jas1957.164927x . The effect of method of feeding upon the susceptibility of the pig to parakeratosis LA Lichten , RJ Cousins . Mammalian zinc transporters: nutritional and physiologic regulation . Ann Rev Nutr , 2009 . 29 153 - 176 . DOI: 10.1146/annurev-nutr-033009-083312 http://doi.org/10.1146/annurev-nutr-033009-083312 . Mammalian zinc transporters: nutritional and physiologic regulation DO Liptrap , ER Miller , DE Ullrey , 等 . Sex influence on the zinc requirement of developing swine . J Anim Sci , 1970 . 30 ( 5 ): 736 - 741 . 5420305 DOI: 10.2527/jas1970.305736x http://doi.org/10.2527/jas1970.305736x . Sex influence on the zinc requirement of developing swine JP Liuzzi , RK Blanchard , RJ Cousins . Differential regulation of zinc transporter 1, 2, and 4 mRNA expression by dietary zinc in rats . J Nutr , 2001 . 131 ( 1 ): 46 - 52 . 11208937 DOI: 10.1093/jn/131.1.46 http://doi.org/10.1093/jn/131.1.46 . Differential regulation of zinc transporter 1, 2, and 4 mRNA expression by dietary zinc in rats JP Liuzzi , JA Bobo , LA Lichten , 等 . Responsive transporter genes within the murine intestinal-pancreatic axis form a basis of zinc homeostasis . Proc Natl Acad Sci USA , 2004 . 101 ( 40 ): 14355 - 14360 . DOI: 10.1073/pnas.0406216101 http://doi.org/10.1073/pnas.0406216101 . Responsive transporter genes within the murine intestinal-pancreatic axis form a basis of zinc homeostasis JP Liuzzi , L Guo , SM Chang , 等 . Krüppel-like factor 4 regulates adaptive expression of the zinc transporter Zip4 in mouse small intestine . Am J Physiol Gastrointest Liver Physiol , 2009 . 296 ( 3 ): G517 - G523 . 19147802 DOI: 10.1152/ajpgi.90568.2008 http://doi.org/10.1152/ajpgi.90568.2008 . Krüppel-like factor 4 regulates adaptive expression of the zinc transporter Zip4 in mouse small intestine RW Luecke , JA Hoefer , WS Brammell , 等 . Mineral interrelationships in parakeratosis of swine . J Anim Sci , 1956 . 15 ( 2 ): 347 - 351 . DOI: 10.2527/jas1956.152347x http://doi.org/10.2527/jas1956.152347x . Mineral interrelationships in parakeratosis of swine XQ Mao , BE Kim , FD Wang , 等 . A histidine-rich cluster mediates the ubiquitination and degradation of the human zinc transporter, hZIP4, and protects against zinc cytotoxicity . J Biol Chem , 2007 . 282 ( 10 ): 6992 - 7000 . 17202136 DOI: 10.1074/jbc.M610552200 http://doi.org/10.1074/jbc.M610552200 . A histidine-rich cluster mediates the ubiquitination and degradation of the human zinc transporter, hZIP4, and protects against zinc cytotoxicity W Maret . Inhibitory zinc sites in enzymes . BioMetals , 2013 . 26 ( 2 ): 197 - 204 . 23456096 DOI: 10.1007/s10534-013-9613-7 http://doi.org/10.1007/s10534-013-9613-7 . Inhibitory zinc sites in enzymes L Martin , U Lodemann , A Bondzio , 等 . A high amount of dietary zinc changes the expression of zinc transporters and metallothionein in jejunal epithelial cells in vitro and in vivo but does not prevent zinc accumulation in jejunal tissue of piglets . J Nutr , 2013 . 143 ( 8 ): 1205 - 1210 . 23761649 DOI: 10.3945/jn.113.177881 http://doi.org/10.3945/jn.113.177881 . A high amount of dietary zinc changes the expression of zinc transporters and metallothionein in jejunal epithelial cells in vitro and in vivo but does not prevent zinc accumulation in jejunal tissue of piglets S Matsuno , E Miyashita , T Ejiri , 等 . Zinc and magnesium output in pancreatic juice after pancreaticoduodenectomy . Tohoku J Exp Med , 1982 . 136 ( 1 ): 11 - 22 . 6176047 . Zinc and magnesium output in pancreatic juice after pancreaticoduodenectomy RJ McMahon , RJ Cousins . Regulation of the zinc transporter ZnT-1 by dietary zinc . Proc Natl Acad Sci USA , 1998 . 95 ( 9 ): 4841 - 4846 . DOI: 10.1073/pnas.95.9.4841 http://doi.org/10.1073/pnas.95.9.4841 . Regulation of the zinc transporter ZnT-1 by dietary zinc B Michalke . Metallomics: Analytical Techniques and Speciation Methods , 2016 . Wiley-VCH, Weinheim, Germany , DOI: 10.1002/9783527694907 http://doi.org/10.1002/9783527694907 . Metallomics: Analytical Techniques and Speciation Methods CF Mills , J Quarterman , RB Williams , 等 . The effects of zinc deficiency on pancreatic carboxypeptidase activity and protein digestion and absorption in the rat . Biochem J , 1967 . 102 ( 3 ): 712 - 718 . 16742484 DOI: 10.1042/bj1020712 http://doi.org/10.1042/bj1020712 . The effects of zinc deficiency on pancreatic carboxypeptidase activity and protein digestion and absorption in the rat FH Nielsen . History of zinc in agriculture . Adv Nutr , 2012 . 3 ( 6 ): 783 - 789 . 23153732 DOI: 10.3945/an.112.002881 http://doi.org/10.3945/an.112.002881 . History of zinc in agriculture D Oberleas . Mechanism of zinc homeostasis . J Inorg Biochem , 1996 . 62 ( 4 ): 231 - 241 . 8676101 DOI: 10.1016/0162-0134(95)00157-3 http://doi.org/10.1016/0162-0134(95)00157-3 . Mechanism of zinc homeostasis BL O'Dell , PM Newberne , JE Savage . Significance of dietary zinc for the growing chicken . J Nutr , 1977 . 65 ( 4 ): 503 - 518 . DOI: 10.1093/jn/65.4.503 http://doi.org/10.1093/jn/65.4.503 . Significance of dietary zinc for the growing chicken NA O'Leary , MW Wright , JR Brister , 等 . Reference sequence (RefSeq) database at NCBI: current status, taxonomic expansion, and functional annotation . Nucleic Acids Res , 2016 . 44 ( D1 ): D733 - D745 . 26553804 DOI: 10.1093/nar/gkv1189 http://doi.org/10.1093/nar/gkv1189 . Reference sequence (RefSeq) database at NCBI: current status, taxonomic expansion, and functional annotation NJ Pace , E Weerapana . Zinc-binding cysteines: diverse functions and structural motifs . Biomolecules , 2014 . 4 ( 2 ): 419 - 434 . 24970223 DOI: 10.3390/biom4020419 http://doi.org/10.3390/biom4020419 . Zinc-binding cysteines: diverse functions and structural motifs R Pieper , L Martin , N Schunter , 等 . Impact of high dietary zinc on zinc accumulation, enzyme activity and proteomic profiles in the pancreas of piglets . J Trace Elem Med Biol , 2015 . 30 30 - 36 . 25744507 DOI: 10.1016/j.jtemb.2015.01.008 http://doi.org/10.1016/j.jtemb.2015.01.008 . Impact of high dietary zinc on zinc accumulation, enzyme activity and proteomic profiles in the pancreas of piglets AS Prasad . Clinical manifestations of zinc deficiency . Annu Rev Nutr , 1985 . 5 ( 1 ): 341 - 363 . 3896271 . Clinical manifestations of zinc deficiency J Raulin . Études cliniques sur la vegetation . Ann Sci Nat Bot Biol Veg Ser, 5:93 , 1869 . (in French) . Études cliniques sur la vegetation KR Robbins , AM Saxton , LL Southern . Estimation of nutrient requirements using broken-line regression analysis . J Anim Sci , 2006 . 84 ( Suppl_13 ): E155 - E165 . 16582088 DOI: 10.2527/2006.8413_supple155x http://doi.org/10.2527/2006.8413_supple155x . Estimation of nutrient requirements using broken-line regression analysis HP Roth , M Kirchgessner . The activity of the pancreas carboxypeptidase A and B during zinc depletion and repletion . Z Tierphysiol Tierernahr Futtermittelkd , 1974 . 33 62 - 67 . (in German) 4833061 . The activity of the pancreas carboxypeptidase A and B during zinc depletion and repletion HP Roth , A Schülein , M Kirchgessner . Influence of alimentary zinc deficiency on digestiblity of nutrients and zinc utilization in force-fed rats . J Anim Physiol Anim Nutr , 1992 . 68 ( 3 ): 136 - 145 . (in German) DOI: 10.1111/j.1439-0396.1992.tb00653.x http://doi.org/10.1111/j.1439-0396.1992.tb00653.x . Influence of alimentary zinc deficiency on digestiblity of nutrients and zinc utilization in force-fed rats HH Sandstead . Requirements and toxicity of essential trace elements, illustrated by zinc and copper . Am J Clin Nutr , 1995 . 61 ( 3 Suppl ): 621S - 624S . 7879727 DOI: 10.1093/ajcn/61.3.621S http://doi.org/10.1093/ajcn/61.3.621S . Requirements and toxicity of essential trace elements, illustrated by zinc and copper B Sandström . Micronutrient interactions: effects on absorption and bioavailability . Brit J Nutr , 2001 . 85 ( Suppl 2 ): S181 - S185 . 11509108 DOI: 10.1049/BJN2000312 http://doi.org/10.1049/BJN2000312 . Micronutrient interactions: effects on absorption and bioavailability FJ Schwarz , M Kirchgessner . Partition and endogenous secretion of Zn given iv. in rats with varying Zn intake . Zbl Vet Med A , 1976 . 23 ( 10 ): 836 - 848 . (in German) DOI: 10.1111/j.1439-0442.1976.tb01502.x http://doi.org/10.1111/j.1439-0442.1976.tb01502.x . Partition and endogenous secretion of Zn given iv. in rats with varying Zn intake M Schweigel-Röntgen . The families of zinc (SLC30 and SLC39) and copper (SLC31) transporters . Curr Top Membr , 2014 . 73 321 - 355 . 24745988 DOI: 10.1016/B978-0-12-800223-0.00009-8 http://doi.org/10.1016/B978-0-12-800223-0.00009-8 . The families of zinc (SLC30 and SLC39) and copper (SLC31) transporters SH Shanklin , ER Miller , DE Ullrey , 等 . Zinc requirement of baby pigs on casein diets . J Nutr , 1968 . 96 ( 1 ): 101 - 108 . DOI: 10.1093/jn/96.1.101 http://doi.org/10.1093/jn/96.1.101 . Zinc requirement of baby pigs on casein diets WH Smith , MP Plumlee , WM Beeson . Zinc requirement for growing swine . Science , 1958 . 128 ( 3334 ): 1280 - 1281 . 13602796 DOI: 10.1126/science.128.3334.1280 http://doi.org/10.1126/science.128.3334.1280 . Zinc requirement for growing swine WH Smith , MP Plumlee , WM Beeson . Effect of source of protein on zinc requirement of the growing pig . J Anim Sci , 1962 . 21 ( 3 ): 399 - 405 . DOI: 10.2527/jas1962.213399x http://doi.org/10.2527/jas1962.213399x . Effect of source of protein on zinc requirement of the growing pig AL Sommer , CB Lipman . Evidence on the indispensable nature of zinc and boron for higher green plants . Plant Physiol , 1926 . 1 ( 3 ): 231 - 249 . 16652481 DOI: 10.1104/pp.1.3.231 http://doi.org/10.1104/pp.1.3.231 . Evidence on the indispensable nature of zinc and boron for higher green plants JW Stevenson , IP Earle . Studies on parakeratosis in swine . J Anim Sci , 1956 . 15 ( 4 ): 1036 - 1045 . DOI: 10.2527/jas1956.1541036x http://doi.org/10.2527/jas1956.1541036x . Studies on parakeratosis in swine WR Todd , CA Elvehjem , EB Hart . Zinc in the nutrition of the rat . Am J Physiol , 1934 . 107 146 - 156 . . Zinc in the nutrition of the rat HF Tucker , WD Salmon . Parakeratosis or zinc deficiency disease in the pig . Proc Soc Exp Biol Med , 1955 . 88 ( 4 ): 613 - 616 . . Parakeratosis or zinc deficiency disease in the pig K Wang , B Zhou , YM Kuo , 等 . A novel member of a zinc transporter family is defective in acrodermatitis enteropathica . Am J Hum Genet , 2002 . 71 ( 1 ): 66 - 73 . 12032886 DOI: 10.1086/341125 http://doi.org/10.1086/341125 . A novel member of a zinc transporter family is defective in acrodermatitis enteropathica BP Weaver , J Dufner-Beattie , T Kambe , 等 . Novel zinc-responsive post-transcriptional mechanisms reciprocally regulate expression of the mouse Slc39a4 and Slc39a5 zinc transporters ( Zip4 and Zip5 ) . Biol Chem , 2007 . 388 ( 12 ): 1301 - 1312 . 18020946 DOI: 10.1515/BC.2007.149 http://doi.org/10.1515/BC.2007.149 . Novel zinc-responsive post-transcriptional mechanisms reciprocally regulate expression of the mouse Slc39a4 and Slc39a5 zinc transporters (Zip4 and Zip5) E Weigand , M Kirchgessner . Total true efficiency of zinc utilization: determination and homeostatic dependence upon the zinc supply status in young rats . J Nutr , 1980 . 110 ( 3 ): 469 - 480 . 7359218 DOI: 10.1093/jn/110.3.469 http://doi.org/10.1093/jn/110.3.469 . Total true efficiency of zinc utilization: determination and homeostatic dependence upon the zinc supply status in young rats W Windisch . Homeostatic reactions of quantitative Zn metabolism on deficiency and subsequent repletion with Zn in 65 Zn-labeled adult rats . Trace Elem Elec , 2001 . 18 ( 3 ): 122 - 128 . . Homeostatic reactions of quantitative Zn metabolism on deficiency and subsequent repletion with Zn in 65Zn-labeled adult rats W Windisch . Interaction of chemical species with biological regulation of the metabolism of essential trace elements . Anal Bioanal Chem , 2002 . 372 ( 3 ): 421 - 425 . 11939527 DOI: 10.1007/s00216-001-1117-6 http://doi.org/10.1007/s00216-001-1117-6 . Interaction of chemical species with biological regulation of the metabolism of essential trace elements W Windisch . Development of zinc deficiency in 65 Zn labeled, fully grown rats as a model for adult individuals . J Trace Elem Med Biol , 2003 . 17 ( 2 ): 91 - 96 . 14531637 DOI: 10.1016/S0946-672X(03)80004-4 http://doi.org/10.1016/S0946-672X(03)80004-4 . Development of zinc deficiency in 65Zn labeled, fully grown rats as a model for adult individuals W Windisch . Effect of microbial phytase on the bioavailability of zinc in piglet diets . Proc Soc Nutr Physiol , 2003 . Effect of microbial phytase on the bioavailability of zinc in piglet diets W Windisch , M Kirchgessner . Measurement of homeostatic adaption of Zn metabolism to deficient and high zinc supply after an alimentary 65 Zn labeling procedure. 1. Effect of different zinc supply on the quantitative zinc exchange in the metabolism of adult rats . J Anim Physiol Anim Nutr , 1994 . 71 ( 1-5 ): 98 - 107 . (in German) DOI: 10.1111/j.1439-0396.1994.tb00344.x http://doi.org/10.1111/j.1439-0396.1994.tb00344.x . Measurement of homeostatic adaption of Zn metabolism to deficient and high zinc supply after an alimentary 65Zn labeling procedure. 1. Effect of different zinc supply on the quantitative zinc exchange in the metabolism of adult rats W Windisch , M Kirchgessner . Zinc excretion and the kinetics of zinc exchange in the whole-body zinc at deficient and excessive zinc supply. 2. Effect of different zinc supply on quantitative zinc exchange in the metabolism of adult rats . J Anim Physiol Anim Nutr , 1994 . 71 ( 1-5 ): 123 - 130 . (in German) DOI: 10.1111/j.1439-0396.1994.tb00349.x http://doi.org/10.1111/j.1439-0396.1994.tb00349.x . Zinc excretion and the kinetics of zinc exchange in the whole-body zinc at deficient and excessive zinc supply. 2. Effect of different zinc supply on quantitative zinc exchange in the metabolism of adult rats W Windisch , M Kirchgessner . Zinc absorption and excretion in adult rats at zinc deficiency induced by dietary phytate additions: I. Quantitative zinc metabolism of 65 Zn-labelled adult rats at zinc deficiency . J Anim Physiol Anim Nutr , 1999 . 82 ( 2-3 ): 106 - 115 . DOI: 10.1111/j.1439-0396.1999.00219.x http://doi.org/10.1111/j.1439-0396.1999.00219.x . Zinc absorption and excretion in adult rats at zinc deficiency induced by dietary phytate additions: I. Quantitative zinc metabolism of 65Zn-labelled adult rats at zinc deficiency W Windisch , U Wher , W Rambeck , 等 . Effect of Zn deficiency and subsequent Zn repletion on bone mineral composition and markers of bone tissue metabolism in 65 Zn-labelled, young-adult rats . J Anim Physiol Anim Nutr , 2002 . 86 ( 7-8 ): 214 - 221 . DOI: 10.1046/j.1439-0396.2002.00377.x http://doi.org/10.1046/j.1439-0396.2002.00377.x . Effect of Zn deficiency and subsequent Zn repletion on bone mineral composition and markers of bone tissue metabolism in 65Zn-labelled, young-adult rats 10.1631/jzus.B1900024 2019-01-15 2019-04-08 2022-01-05 Copyright © Zhejiang University and Springer-Verlag GmbH Germany, part of Springer Nature 2019 2019 Journal of Zhejiang University-SCIENCE B (Biomedicine and Biotechnology) 08 20