Zinc is an essential trace mineral crucial to growth, enzyme systems, immunity, reproduction and antioxidant defense system as a co-factor to Superoxide Dismutase enzyme. Probiotics are well known for improving digestion and utilization of nutrients and minerals by producing digestive enzymes and volatile fatty acids and alleviating heat stress through stabilization of normal microflora disrupted under heat stress. Our study investigated the individual as well as synergistic effects of Zinc and Protexin, on redox status, thyroid hormones and liver enzymes in broilers reared under cyclic heat stress as no literature was documented so far on the given subject as far as our discretion goes.
Our experimental trial included 224 d-old broilers randomly segregated into seven groups of eight replicates each. Group A (TN control) was fed basal diet (BD) only, Group B (HS) was given BD and exposed to 35 ± 1.1°C; 75 ± 5% RH heat stress whereas the remaining groups C, D, E, F and G were given diets supplemented with 30mg ZnSO4/kg BD, 60mg ZnSO4/kg BD, 0.1g Protexin®/kg BD, 30mg/Kg feed ZnSO4 + 0.1g/Kg feed Protexin®, 60mg/Kg feed ZnSO4 + 0.1g/Kg feed Protexin® respectively along with 8 hourly cyclic heat stress (35 ± 1.1°C; 75 ± 5% RH). Two birds per replicate were slaughtered at the end of trial to collect whole blood, serum, pectoralis muscle and liver tissue for biochemical analyses.
Results showed that heat stress caused significant (p<0.05) elevation in whole blood, serum, muscle and liver MDA levels in heat stress (HS) group. Serum AST, ALT, Glucose, Urea and Uric acid were also significantly (p<0.05) raised in the HS group. Catalase activity was significantly (p<0.05) increased in whole blood, serum and liver of birds belonging to HS group and in pectoralis muscle of birds in Com60 group. Moreover, serum T3 was significantly (p<0.05) reduced in the HS group. All dietary supplementations significantly (p<0.05) reduced MDA levels (whole blood, serum, muscle and tissue), serum AST and ALT and significantly (p<0.05) increased serum T3 concentration. Broilers supplemented with combination of ZnSO4 (30mg/kg diet) and Protexin (0.1g/kg diet) exhibited lowest MDA, AST, ALT, Urea, Uric acid and Glucose concentrations compared to other diets. No significant changes were observed in serum T4 and Creatinine concentrations.
Based on our findings, it can be concluded that dietary supplementation of Zinc or Protexin either alone or specifically combined can effectively attenuate adverse effects of heat stress and can be safely incorporated as a novel supplement in broilers’ feed to reduce lipid per oxidation however further studies are recommended in order to elucidate and confirm our results.