Effects of sodium humate and zinc oxide used in prophylaxis of post-weaning diarrhoea on the health, oxidative stress status and fatty acid profile in weaned piglets

The aim of this study was to investigate the effects of sodium humate (HNa), applied to feed or drinking water as a partial substitution for pharmacological doses of ZnO, on clinical, biochemical and haematological indicators of health status, oxidative stress and the serum fatty acid (FA) profile in weaned piglets. Weaned piglets (32) were allocated into four groups: Control = basal diet containing 110 mg ZnO/kg; ZnO 2.5 = pharmacological dose of ZnO (2.5 g ZnO/kg); ZnO 1.7 + HNa (f) = 1.7 g ZnO and 20.0 g HNa/kg; ZnO 1.7 + HNa (w) = 1.7 g ZnO/kg and drinking water with 0.2% HNa. All ZnO treatments resulted in good performance and clinical health of piglets in contrast to Control, which contained three diarrhoeic piglets. Increased triacylglycerols in the ZnO 2.5 and ZnO 1.7 + HNa (w) groups in comparison with Control suggested increased energy metabolism after treatments. Neither total cholesterol, nor HDL and LDL were affected by treatments. Piglets treated with ZnO and HNa had (ZnO 1.7 + HNa (w)) or tended to have (ZnO 1.7 + HNa (f)) lower urea in serum. Significantly (in ZnO 2.5 and ZnO 1.7 + HNa (f)) or non-significantly (ZnO 1.7 + HNa (w)) higher haematocrit and haemoglobin levels were detected in the blood of treated piglets. Long-term ZnO 2.5 treatment significantly increased serum 8-iso-PGF2α, the most reliable biomarker of oxidative stress. Partial substitution of ZnO by HNa positively affected the oxidative status of piglets as evidenced by significant (ZnO 1.7 + HNa (w)) or non-significant (ZnO 1.7 + HNa (f)) declines in serum 8-iso-PGF2α. ZnO 2.5 treatment significantly decreased saturated (SFA), monounsaturated (MUFA) and n-3 polyunsaturated FA (PUFA) and increased PUFA n-6 and n-6/n-3 ratios in serum compared to Control. The synthesis of some physiologically significant long-chain PUFA (LC-PUFA), namely n-6 dihomo-γ-linolenic acid and n-3 eicosapentaenoic, docosapentaenoic was negatively affected by ZnO 2.5 treatment. Both ZnO 1.7 + HNa (f)/(w) treatments significantly increased the proportion of SFA and PUFA n-3 and decreased PUFA n-6 and n-6/n-3 ratios in comparison with ZnO 2.5 and the effect was more considerable in ZnO 1.7 + HNa (w). Most individual PUFA n-3 and n-6 as well as the n-6/n-3 ratio in both treatments were similar to Control. The results indicate that the partial substitution of ZnO by HNa can benefit performance and health of weaned piglets to a similar extent as a high pharmacological dose of ZnO, whereas it can decrease the oxidative stress induced by prolonged over-supplementation of ZnO. Additionally, such a treatment can eliminate the unfavourable effect of high ZnO doses on the n-6/n-3 ratio and the proportion of some physiologically significant LC-PUFA in serum. Generally, it can be concluded that the effects of feed and water HNa supplementation are similar, but are more pronounced when HNa is applied to drinking water.