*3.1. Growth Performance*

During the whole experimental period, no form of feed supplementation with Zn from any source influenced either feed intake or body weight/gain compared to unsupplemented control lambs (Table 2).

**Table 2.** Growth performance of lambs for the 120 day feeding period differing in Zn source (80 mg Zn/kg). ADFI: average daily feed intake; ADG: average daily gain.


1 C: basal diet, ZnSO4: zinc sulphate, ZnGly: zinc chelate of glycine hydrate, and ZnProt: zinc chelate of protein hydrolysate. 2 Values (*n* = 8/treatment) are presented as the least squares means.

## *3.2. Mineral Status*

The 120 day period of feed supplementation with organic Zn proteinate (ZnProt) increased the plasma Zn concentration compared to the control treatment (*p* = 0.028, Table 3), while the MT concentration in plasma was reduced during the ZnProt treatment (*p* < 0.05). Plasma Cu concentration increased with ZnSO4 treatment compared to the control and ZnProt treatments (*p* < 0.01) and, therefore, the highest Zn/Cu ratio was observed in the plasma of lambs fed the diet enriched with ZnProt (*p* < 0.01). Plasma concentrations of zinc did not differ between the dietary treatments after 30, 60, and 90 days of Zn supplementation; however, the effects of time and treatment were detected (Supplementary Materials, Table S1). Concentrations of Cu and Fe in plasma were not affected by dietary treatments in all collection periods (i.e., 30, 60, and 90 days of Zn supplementation), but the time effect was detected in both minerals (Table S1).

Feed supplementation with Zn sulphate increased Zn concentration in liver tissue (*p* < 0.05) compared to the control treatment (Table 4). The diet with ZnProt significantly increased Zn concentrations in the kidney cortex compared to other treatments (*p* < 0.01). Zn concentrations in other tissues (muscles, spleen, pancreas, heart, rib bone) were not affected by the dietary treatment.


**Table 3.** Activity of antioxidant enzymes (i.e., SOD and GPx) in blood, plasma mineral concentration, and other plasma parameters of lambs fed diets (80 mg Zn/kg) differing in Zn source after the 120 day feeding period.

SOD: superoxide dismutase, GPx: glutathione peroxidase, MT: metallothionein, ALB: albumin, TSH: total thiol groups, TAS: total antioxidant status, and MDA: malondialdehyde. 1 C: basal diet, ZnSO4: zinc sulphate, ZnGly: zinc chelate of glycine hydrate, and ZnProt: zinc chelate of protein hydrolysate. 2 Values (*n* = 6/treatment) are presented as the least squares means. Means within lines with different superscript letters are significantly different (*p* < 0.05).

**Table 4.** Tissue Zn concentrations in lambs fed diets differing in Zn source (80 mg Mn/kg) for the 120 day feeding period.


1 C: basal diet, ZnSO4: zinc sulphate, ZnGly: zinc chelate of glycine hydrate, and ZnProt: zinc chelate of protein hydrolysate. 2 Values (*n* = 6/treatment) are presented as the least squares means. Means within lines with different superscript letters are significantly different (*p* < 0.05).

The tissue concentrations of Mn, Fe, and Cu in liver, kidney, muscles, spleen, pancreas, heart and rib bone are presented in Table 5. Increased Cu concentrations in the pancreas and decreased Mn concentrations in the heart muscle were observed in the lambs fed diets supplemented with both organic Zn sources (*p* < 0.01 and *p* < 0.05, respectively). The ZnProt-enriched diet decreased liver Cu concentrations compared to the control lambs (*p* < 0.05). Cu concentrations increased in the kidney cortex of lambs given ZnSO4 and ZnGly treatments compared to the control animals (*p* < 0.001). Feed supplementation with ZnGly decreased Fe concentrations in kidney and muscles (*m. psoas major*) compared to ZnProt treatment (*p* < 0.05) and decreased muscle Mn (*m. longissimus dorsi*) compared with ZnSO4 but increased Mn concentrations in the pancreas in comparison with the control and ZnProt treatments. Intake of the diets supplemented with Zn from both organic sources decreased Fe concentrations in the heart compared to the control and ZnSO4 treatment (*p* < 0.01).


**Table 5.** Tissue concentrations of Cu, Fe, and Mn in lambs fed diets differing in Zn source (80 mg Mn/kg) for the 120 day feeding period.

1 C: basal diet, ZnSO4: zinc sulphate, ZnGly: zinc chelate of glycine hydrate, and ZnProt: zinc chelate of protein hydrolysate. 2 Values (*n* = 6/treatment) are presented as the least squares means. Means within lines with different superscript letters are significantly different (*p* < 0.05).
