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To assess the efficacy of bis-glycinate bound Zn, 36 crossbred wethers (34 ± 2 kg) were sorted by body weight into three groups and stagger started on a Zn-deficient diet (18 mg Zn/kg dry matter [DM]; 22.5% neutral detergent fiber [NDF]) for 45 d prior to a 15-d metabolism period (10 d adaptation and 5 d collection). On day 46, lambs were randomly assigned to dietary treatments (four lambs treatment-1group-1): no supplemental Zn (CON) or 15 mg supplemental Zn/kg DM (ZINC) as Zn sulfate (ZS) or bis-glycinate (GLY; Plexomin Zn, Phytobiotics). Blood was collected from all lambs on days 1, 44, 56, and 61. Liver, jejunum, and longissimus dorsi samples were collected after euthanasia on day 61. Gene expression was determined via quantitative real-time polymerase chain reaction. Data were analyzed using ProcMixed of SAS (experimental unit = lamb; fixed effects = treatment, group, and breed) and contrast statements assessed the effects of supplemental Zn concentration (ZINC vs. CON) and source (GLY vs. ZS). After 15 d of Zn supplementation, plasma Zn concentrations were greater for ZINC vs. CON and GLY vs. ZS (P ≤ 0.01); tissue Zn concentrations were unaffected (P ≥ 0.27). Liver Cu concentrations were lesser for ZINC vs. CON (P = 0.03). Longissimus dorsi Mn concentrations were greater for ZINC vs. CON (P = 0.05) and tended to be lesser for GLY vs. ZS (P = 0.09). Digestibility of DM, organic matter (OM), and NDF was lesser for ZINC vs. CON (P ≤ 0.05); acid detergent fiber digestibility tended to be greater for GLY vs. ZS (P = 0.06). Nitrogen retention (g/d) tended to be greater for GLY vs. ZS (P = 0.10), and N apparent absorption was lesser for ZINC vs. CON (P = 0.02). Zinc intake, fecal output, retention, and apparent absorption were greater for ZINC vs. CON (P ≤ 0.01). Apparent absorption of Zn was -5.1%, 12.8%, and 15.0% for CON, ZS, and GLY, respectively. Nitrogen and Zn retention and apparent absorption were not correlated for CON (P ≥ 0.14) but were positively correlated for ZINC (retention: P = 0.02, r = 0.52; apparent absorption: P < 0.01, r = 0.73). Intestinal expression of Zn transporter ZIP4 was lesser for ZINC vs. CON (P = 0.02). Liver expression of metallothionein-1 (MT1) tended to be greater for GLY vs. ZS (P = 0.07). Although Zn apparent absorption did not differ between sources (P = 0.71), differences in post-absorptive metabolism may be responsible for greater plasma Zn concentrations and liver MT1 expression for GLY-supplemented lambs, suggesting improved bioavailability of GLY relative to ZS., (© The Author(s) 2021. Published by Oxford University Press on behalf of the American Society of Animal Science.)

Apical uptake of zinc as ionic Zn(II) or as Zn-methionine (Zn-Met) was studied in RTgutGC cell line in vitro under media compositions mirroring the gut luminal ionic concentration of freshwater (FW) and seawater (SW) acclimated salmonids. Viability of the RTgutGC cells exposed to experimental media preparations showed a time-dependent decrease in SW treated cells, with the effect being significant at 48 h (P < 0.01), but not at 12 h or 24 h. Half effective concentration of Zn exposure over 12 h (EC 50 , in μM) was not differentially affected by media composition (FW, 59.7 ± 12.1 or SW, 83.2 ± 7.2; mean ± SE, P = 0.43). Zinc ( 65 Zn) influx in RTgutGC was not different between FW or SW treated cells, but increased significantly in the presence of methionine (2 mM, L-Met or DL-Met). An interaction effect was observed between Zn concentration and media ionic composition on the impact of Met on apical Zn uptake (L-met, P < 0.001; DL-met, P = 0.02). In the presence of Met, apical Zn uptake in SW medium was significantly lower compared to FW, but only at higher Zn concentrations (12 and 25 μM, P < 0.01). Further, Met facilitated Zn uptake was reduced in cells treated with an amino acid transport system blocker with the effect being more significant and stereospecific in SW ionic conditions. The findings of this study showed that (i) Zn speciation in the presence of Met improved apical Zn uptake in RTgutGC cells and Zn-Met species were possibly taken up through Met uptake system. (ii) The effect was differentially affected by the ionic composition of the medium. Implications and limitations of the observations towards practical Zn nutrition of salmonids are discussed., (Copyright © 2018 The Authors. Published by Elsevier GmbH.. All rights reserved.)

Abstract The use of vegetable ingredients may alter the mineral balance of feeds for gilthead seabream (Sparus aurata) due to the differences in mineral composition between marine and vegetable ingredients. Whereas seabream fed low levels of zinc (Zn) and manganese (Mn) may present reduced growth and performance, as well as alterations in mineral deposition and oxidative stress resistance, information on the type of sources of these two minerals is almost inexistent. In the present study, vegetable meal and oil (VM/VO) based diets were formulated including the target minerals, zinc (Zn) and manganese (Mn) in two different delivery forms, oxides and chelated to amino acids. Gilthead seabream of 8.2g were fed one of five different diets containing either non mineral supplementation, Zn and Mn oxides, amino acid chelates and their combinations. During the experimental period, fish fed Zn oxide presented higher growth, a higher deposition of protein and lower lipid contents in whole body, whereas there was an increase in whole body TBARs and up-regulation of CuZnsod in fish fed diets supplemented with amino acids chelated Zn. Highlights • Dietary mineral uptake varies depending on the source used. This study aims to overcome the shortcomings of other studies regarding mineral-specific effects in Sparus aurata. • Zn and Mn supplementation improve seabream growth, body composition and mineral retention when gilthead seabream are fed diets containing high levels of plant ingredients • Zn oxide improved growth, feed efficiency, lipid and protein deposition and oxidative status related parameters. The effects were not so clear for the Mn sources [ABSTRACT FROM AUTHOR]

Zinc is both a vital nutrient and an important toxicant to aquatic biota. In order to understand the interplay between nutrition and toxicity, it will be important to determine the mechanisms and the factors that regulate zinc uptake. The mechanism of apical intestinal Zn(II) uptake in freshwater rainbow trout and its potential modification by the complexing amino acid histidine was investigated using brush-border membrane vesicles (BBMVs). Following characterisation of the BBMV preparation, zinc uptake in the absence of histidine was both time- and concentration-dependent and consisted of two components. A saturable phase of uptake was described by an affinity constant of 57±17 μM and a transport capacity of 1867±296 nmol mg membrane protein−1 min−1. At higher zinc levels (>500 μM) a linear, diffusive component of uptake was evident. Zinc transport was also temperature-dependent, with Q10 values suggesting zinc uptake was a carrier-mediated process. Zinc uptake by vesicles in the presence of histidine was correlated to a mono-histidine species (Zn(His)+) at all Zn(II) concentrations examined. [Copyright &y& Elsevier]