The means of antioxidant parameters such as total antioxidant, SOD, catalase and TBARS are presented in Table 1.
Total antioxidant capacity
Highly significant (P<0.01) increase was noticed in the T2 group followed by the T1 group as compared to the T0 group on TAC. The findings in the present study are in accordance with
Shen et al., (2021) and
Patel et al., (2021). In contrast,
Ulutas et al., (2020) reported no significant change in antioxidant activity after zinc supplementation. This may be due to the fact that environmental and feeding factors caused no oxidative stress for the animals.
Superoxide dismutase
The SOD differed significantly (P<0.01) in the T1 and T2 groups compared to the control group. Similar findings were also reported by
Patel et al., (2021) and
Nagalakshmi et al., (2009) on zinc supplementation. The increase in SOD activity after zinc supplementation might be because zinc is an intrinsic constituent of superoxide dismutase, a major scavenger of free radicals present in the cytoplasm of many types of cells
(Spears and Weiss, 2008). In copper supplemented groups, the present study’s findings are in accordance with
Zhang et al., (2012) and
Correa et al., (2014).
Catalase
Significant (P<0.01) difference was noticed in T0, T1 and T2 groups. The findings were in accordance with
Nagalakshmi et al., (2009) in catalase activity after supplementing zinc to lambs. Zinc plays an essential role in catalase activity, regulating specificity protein 1 or other transcriptional response elements
(Tate et al., 1995). However, copper also increases the catalase activity in Guizhou goats
(Shen et al., 2021).
TBARS
TBARS was significantly (P<0.01) higher in T0 followed by T1 and T2 in the present study. Similar findings were reported by
Ulutas et al., (2020) in goats and
Wei et al., (2019) in newborn dairy calves, zinc supplementation significantly decreased malondialdehyde (MDA) levels, which might be due to the antiperoxidative activity of zinc on lipids where the zinc stabilizes the membrane structures by antagonizing redox-active metals such as iron and copper
(Shaheen and El-Fattah, 1995). In the copper supplemented group, the results were in accordance with
Zhang et al., (2012) and
Shen et al., (2021).
The means of biochemical parameters such as total protein, albumin, globulin, glucose, cholesterol and triglycerides are presented in Table 2.
Total proteins
Higher means values were noticed in the zinc supplemented group (P<0.01) as compared with T0 and T1 groups. The difference between T0 and T1 groups was non-significant. Our results are compatible with the findings of
Anil et al., (2020) and Fagari-
Nobijari et al., (2012). However,
Sobhanirab et al., (2012) and
Sethy et al., (2016) reported non-significant differences in total proteins in zinc supplemented group. Similarly,
Wu et al., (2014) and
Naseri et al., (2011) also reported non-significant differences in total proteins in the copper supplemented and control group, which were in accordance with our findings. The elevated serum protein levels of the zinc supplemented group in the present study indicated that zinc might have been involved in better assimilation of protein from an available dietary protein source
(Grela and Pasuszak, 2004) by optimum production and activities of various proteolytic enzymes like carboxypeptidase A and carboxypeptidase B. The significantly higher total serum protein in zinc supplemented animals might have helped in maintaining well organized vital functions of proteins like maintenance of osmotic pressure of blood and tissue, the acid-base balance of blood, the activity of enzymes and peptide hormones, antibodies and clotting factors
(Borah et al., 2014).
Albumin
Significantly (P<0.01) higher overall mean values were noticed in the T2 group, whereas the difference between T0 and T1 was non-significant (P>0.05). Our results are in accordance with
Fagari-Nobijari et al., (2012) in Holstein bulls. Whereas,
Sobhanirab et al., (2012) and
Sethy et al., (2016) reported no significant differences in zinc supplementation as compared to control groups. Similarly,
Naseri et al., (2011) and
Wu et al., (2014) also reported no significant differences in albumin concentration after copper supplementation. The non-significant increasing trend of serum albumin from day 0 onwards till day 90 in the present experiment reflects that supplementation of zinc or zinc deficiency might not directly affect serum albumin concentration
(Borah et al., 2014).
Globulin
No significant change was noticed between groups in the overall means. But numerically zinc supplemented group showed higher values. The improved globulin levels on zinc supplementation could be related to zinc’s functional role in protein synthesis and this improved globulin level indicates a better immune response, as serum globulins play a significant role in immune response (immunoglobulins or antibodies) and early line of defence
(Anil et al., 2020).
Glucose
There was also no significant difference (P>0.05) between treatment groups in the overall means. Whereas,
Sethy et al., (2016) reported a significant increase in glucose levels on zinc supplementation in black Bengal goats. The findings of
Sethy et al., (2016) might be due to reduced activity of carbohydrate digesting enzymes, which are reliant on dietary zinc levels, which might cause the decreased blood glucose levels in zinc supplemented groups. However,
Hesari et al., (2012) found no significant increase in glucose concentrations after copper supplementation, which was in accordance with our findings. Copper is required for defence mechanisms, iron transport, cholesterol and glucose metabolism and brain development
(Felltman, 1991).
Total cholesterol
Highly significant (P<0.01) decrease was noticed in the T1 group compared with T2 and T0 groups. Our findings are in agreement with the results of
Samanta et al., (2011) and
Zhang et al., (2012). However, our findings of zinc supplementation when compared with the control group are similar to the results reported by
Ulutas et al., (2020) and
Sobhanirab et al., (2012) who found no significant changes in cholesterol levels.
Nobijari et al., (2012) reported a significant decrease in cholesterol after zinc supplementation in Holstein bulls. They further stated that this might be indirectly due to the decreased availability of blood glucose in zinc supplemented groups because glucose also acts as a source for cholesterol production in the biological system. While
Sung and Dale, (1981) claimed that Zn has a positive correlation with blood cholesterol levels.
Triglycerides
Significantly (P<0.01) higher mean values were observed in the T2 group, followed by T1 and lower values in the T0 group. The difference between T0 and T1 groups remained non-significant. The findings of present investigation are similar to the results published by
Sobhanirab et al., (2012) in cows, in the zinc supplemented group. This might be because zinc plays a direct role in the regulation of lipid metabolism and has structural and functional characteristics of lipid enzymes
(Ulutas et al., 2020). While
Zhang et al., (2012) and
Guclu et al., (2008) reported no significant difference in triglyceride levels between copper supplemented and control group.