This study investigated the relative bioavailability (RBV) of zinc from different sources used as feed additives in ruminant nutrition based on Zn concentration and the activity of Zn-dependent enzymes in lamb tissues. Thirty-two male lambs of Improved Valachian breed (three months old) were randomly assigned to four dietary treatments. For 120 days, the lambs were fed either the total mix ration (TMR) providing 29.6 mg Zn/kg or the TMR supplemented with either zinc sulphate (ZnSO4), zinc chelate of glycine hydrate (ZnGly), or zinc chelate of protein hydrolysate (ZnProt). The supplemented diets contained a total of 80 mg Zn/kg. Supplementation with ZnSO4 increased Zn concentration in the liver, while the highest Zn uptake was in the kidneys of lambs fed the ZnProt diet. The ZnGly supplemented diet elevated the activity of the Cu/Zn-dependent enzyme superoxide dismutase (Cu/Zn SOD) in the liver. Regardless of Zn source, Zn supplementation resulted in increased total antioxidant status (TAS) in the pancreas. The estimated RBV of Zn based on linear regression slope ratios did not differ among the Zn sources. Our results indicate similar availability of Zn from organic dietary sources as from commonly used zinc sulphate; however, their effects on mineral and antioxidant status may differ slightly in growing lambs.

Findings that Zn and fibre source affected the nutrient apparent total tract digestibility (ATTD), made us hypothesize that interactions could occur affecting the apparent digestibility of Zn and trace elements (TEs) interacting with Zn in the digestive tract. Therefore, the study investigated the effects of Zn and fibre sources on the apparent digestibility and solubility of TEs (Zn, Cu, Fe, Mn) and pH in the small intestinal segments of 40-days-old piglets. In vitro solubility of TEs was estimated using a simulated digestion assay. Feed supplementation with potato fibre (PF) affected the ATTD of all TEs and dry matter as well as mineral solubility in the ileum and/or jejunum without any effect on pH in the small intestine. Intake of PF enhanced Zn and Cu absorption (p < 0.01), but significantly decreased ATTD of Fe and Mn (p < 0.001). Diet supplementation with Zn glycinate decreased Zn absorption in the gut (p < 0.01) and affected the solubility of other TEs in the different digestion phases. Although in vitro solubility of TEs does not provide a good prediction of mineral bioaccessibility, using a combination of in vitro and in vivo methods can enable prediction of the trace mineral absorption.