Aims:  To evaluate the free radical‐scavenging capacity of Lactobacillus fermentum and its effects on antioxidant enzyme levels in finishing pigs. Methods and Results:  The free radical‐scavenging activity of Lact. fermentum was analysed in vitro. The tested Lactobacillus showed a high scavenging ability against DPPH (1,1‐diphenyl‐2‐picrylhydrazyl), superoxide and hydroxyl radicals which was dose dependent. Subsequently, 108 crossbred pigs weighing 20·67 BW, were allotted to dietary treatments including a basal diet or the basal diet supplemented with either aureomycin or 10·2 × 107 Lact. fermentum CFU g−1 diet. Supplementation of Lact. fermentum increased total antioxidant capacity (P < 0·01) in serum from 50 kg pigs, while serum superoxide dismutase (P = 0·01) and glutathione peroxidase (P < 0·01) increased, and malondialdehyde levels decreased (P < 0·01) in 90 kg pigs. Hepatic catalase (P = 0·04), muscle superoxide dismutase (P < 0·01) and copper–zinc‐superoxide dismutase were enhanced (P = 0·01), whereas malondialdehyde levels were reduced (P = 0·05) by Lact. fermentum. Conclusions:  The free radical‐scavenging capacity of Lact. fermentum was dose dependent and its supplementation improved the antioxidant status of pigs. Significance and Impact of the Study:  Lactobacillus fermentum could be used to alleviate oxidative stress and increase pig performance and improve pork quality.

Aims: To determine the effects of Lactobacillus fermentum I5007 on the redox state of piglets oxidatively stressed with diquat. Methods and Results: Twenty-four, 28-day-old barrows were used in a 2 9 2 factorial design experiment with the main effects being Lact. fermentum supplementation and diquat challenge. Half of the pigs (n = 12) were orally administered with 20 ml of a solution containing 10 8 CFU ml À1 ofLact. fermentum each morning of the 21-day trial, while the remainder received saline. On day 8, these two groups were further subdivided so that half of the pigs in each group (n = 6) were intraperitoneally injected with 10 mg kg À1BW diquat, while the remainder received saline. The diquat-injected pigs had significantly poorer performance and increased levels of plasma cortisol, adrenaline, carbonyl and malondialdehyde. Lactobacillus fermentum supplementation significantly increased superoxide dismutase and glutathione and increased the ability to inhibit superoxide anion production in liver and muscle. Conclusions: Lactobacillus fermentum improved the anti-oxidative defence system and alleviated damage caused by diquat. Significance and Impact of the Study: Lactobacillus fermentum has the potential to alleviate oxidative stress and improve weaning pig performance.