Heat stress demands high dietary zinc to combat oxidative stress, and improve cytokine and immune response in rats

Abstract

Heat stress (HS) adversely impacts livestock production, immune response, and antioxidant status. Zinc (Zn), a key component of metalloenzymes, plays a vital role in maintaining these functions, with increased Zn requirements likely under HS. This study determined the dietary Zn requirement of rats under HS. Seventy-two weaned Wistar rats were allocated into six groups in a 3 × 2 factorial design (3 Zn levels: 14.6 ppm (CON), 32.7 ppm (Zn1), and 48.9 ppm (Zn2); 2 environmental conditions: thermoneutral (TN) and HS. All groups received the same basal purified diet with varying dietary Zn supplied as zinc sulphate (ZnSO₄.7H₂O). Initially for 28 days all groups were maintained under TN condition, later three groups from each dietary Zn levels were exposed to HS (5 hr/d) for 14 days in a psychrometric chamber. Blood, serum, and organ samples were analyzed for biochemical, hormonal, immune, and mineral profiles. HS elevated stress markers (cortisol, malondialdehyde, cytokines, haptoglobin, alanine transaminase, and aspartate transaminase), while higher dietary Zn (48.9 ppm) significantly reduced these markers under HS. Antioxidant enzymes (superoxide dismutase and catalase) and humoral immune response were lower in control groups but improved with increased dietary Zn in both environments. The mineral concentrations of Zn, Cu, Mn, and Fe in serum were increased with higher dietary Zn levels in HS compared to TN groups. In conclusion, higher dietary Zn level at 48.9 ppm in a purified diet is effective in alleviating HS by lowering stress markers and bolstering antioxidant enzymes and humoral immune responses.