Effect of substituting increasing levels of organic Zn for inorganic Zn on performance, hematological and serum biochemical constituents, antioxidant status and immune response in rat.

The effect of replacing dietary Zn supplemented from inorganic (ZnCO3) source with organic Zn (Zn methionine; Zn-met) was investigated in 72 rats (98.42 ± 1.483 g) by randomly allotting to 4 diets (6 replicates/diet, 3 rats/replicate). Basal diet was prepared with purified ingredients without Zn. The control diet (AIN-76A) contained 12 ppm of Zn from ZnCO3 (100-I). In the other diets ZnCO3 was replaced with Zn-met at the rates of 50 (50I:50O), 75 (25I:75O) or 100% (100-O). Weekly body weight and daily feed intake were recorded for 14 weeks. Blood was collected by retro-orbital puncture on the 70th and 80th day to determine haematological and various serum biochemical constituents, and antioxidant enzyme activities in haemolysate, respectively. Rats were antigenically challenged with sheep RBC on day 73 to assess humoral immune response (HIR), and on day 95 for cell mediated immune response (CMIR) and rats were sacrificed at the end of rearing period to collect liver, muscle, pancreas and kidneys for Zn estimation and oxidative stress markers in liver. The data were analysed using completely randomized design. Weight gain and feed intake, hematological and serum biochemical constituents, Zn content in organs (except liver) were not influenced by replacing ZnCO3 with Zn-met. Zinc concentrations in the serum and liver were higher (P<0.05) with 50% replacement of ZnCO3 with Zn-met compared to 0 or 100% replacement. Lower (P<0.05) lipid peroxidation and higher (P<0.05) glutathione peroxidase and glutathione reductase activities were observed with 50 and 75% replacement of ZnCO3 with Zn-met compared to 0 or 100% replacement. Protein carbonyls and reduced glutathione in liver were not affected, while TBARS decreased (P<0.05) with substituting Zn-met (50-100%) for ZnCO3. The HIR and CMIR increased with increasing Zn-met supplementation and the highest response was observed with 75-100% replacement of ZnCO3 with Zn-met. It is concluded that replacement of 50 or 75% of ZnCO3 with Zn-met increased antioxidant and immune response in rats with no effect on growth.